Birds
It is not only fine feathers that make fine birds. ~ Greek fabulist Aesop
With over 18,000 extant species, birds are the most speciose class of tetrapods. The living descendants of dinosaurs, birds have had ample time to adapt and diversify. Birds live most everywhere that a macroscopic animal might. All are feathered, winged, bipedal, endothermic egg layers, with beaks but no teeth.
Wings are an evolutionary fashion from forelimbs. The now extinct moa of New Zealand, hunted to extermination by humans, was the only known bird without wings. Most birds can fly, but a few, including penguins and endemic island species, forsook flight.
Birds have light but strong skeletons, 4-chambered hearts, and a high metabolic rate. They range in size from the 5 cm, 2 g bee hummingbird to the 2.75 m, 125 kg ostrich.
Diet
Most birds eat other animals. Avivorous birds, such as raptors, eat other birds. All birds of prey are carnivorous, as are many other birds, including different wading birds, shorebirds, and some corvids.
Seabirds are typically piscivorous: feeding on fish. Pelicans, cormorants, loons, and grebes dive to thrive on aquatic food. Other piscivores patiently try their luck in lurking to pluck, most notably the heron, a wading bird.
Several shorebirds are molluscivores, foraging in tidal flats and swamps. Most are well equipped to deal with the shells that mollusks use to protect themselves.
Snake eating (ophiophagy) is a specialization. Easier fare is found by foraging insects: a diet common to several small birds, including swifts, swallows, flycatchers, and warblers.
Most birds enjoy insects, at least as a supplement. Insects are often a critical source of protein for growing nestlings. Many fledglings are fed insects by their parents even if their mature diet will be quite different.
A few birds are omnivores, the best known being the duck. Many birds will sample foods other than their primary preference. Variety is often the spice of avian life.
Herbivorous birds are somewhat atypical. Despite the appearance of easy pickings, plants are a digestive challenge compared to animals. Per weight, plants are less nutritious and require more digestive processing.
Herbivorous birds often have smaller relatives who are carnivores, as it is otherwise hard to get enough nutritional energy. Most herbivorous birds feed on seeds (granivory), the most nutritious plant food. Game birds (e.g., turkeys, quail, geese, dove), sparrows, and finches are granivorous. Most have specialized bills to crack the specific shells of favored fare. Many granivores, such as peafowl, turkeys, and chicken, have muscular gizzards, which they may pack with stones. This lets them swallow seeds whole and crush them within: an internal digestive mill.
A few birds are into the sweet stuff: nectar, sometimes with a pollen pick-me-up (palynivory). Hummingbirds are the best known nectivores, though sunbirds, honeycreepers, orioles, and the bananaquit are also nectar lovers. The bananaquit, native to the Caribbean islands, Central and South America, is so brazen that it will fly into open windows of homes to steal sugar; hence earning the nickname sugar bird.
Fruit is a fine food, but often seasonal; though tropical forests may bear fruit year-round. When fruit does turn up, it tends to be profusely abundant.
Orangutans are the largest committed fruit eaters (frugivores). Abundance is no problem for an animal of such girth. Orangutans tend to dine alone or in small family groups.
By contrast, most small fruit eaters – monkeys and most fruit-eating birds – forage in groups. That improves the odds of finding fruit, which, when found, there is often enough to go around. This communal strategy is used by other birds facing hard-to-find feasts, including turkeys and vultures.
Hornbills
The sociality engendered by foraging often spills over in other facets of life. Hornbills are fruit eaters and have gregarious lifestyles.
Ground hornbills are not fruit lovers. They are instead formidable predators, with a beak like an icepick. This hornbill can hack its way into a tortoise.
Ground hornbills probably descended from frugivores. Their sociality took a turn with their diet. As predators, they hunt in packs, usually family groups.
Some ground hornbills in a hunting pack act as chasers. Others lurk, acting as beaters to scare the prey on, until it runs into the one that takes it down.
Songbird Patience
Small songbirds lose up to 10% of their body weight overnight, so they must eat well every day. There is a trade-off. Weight gain slows them down, leaving them vulnerable to predators. So, every morning, birds leave their nests and scout for food, assessing the location and quality of fare without eating.
By fasting in the morning, a bird remains nimble enough to dodge predators during daylight hours. As afternoon wears on, birds return to eat, already knowing the best places to dine.
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Cellulose, the fiber of leaves, is pure carbohydrate, but hard to digest. Small endotherms can’t pack in enough cellulose and microbes to fuel their high metabolic rate. Termites triumph in that trick by not having to keep themselves warm.
A bird must be at least as a big as a grouse to have a go at being a folivore. Ostriches, with a huge body and relatively low metabolic rate, forage on vegetarian fare; though an ostrich enjoys the odd animal bite when the opportunity arises.
Ostriches often graze side by side with zebra. The two might seem to be eating from the same menu, but their selections are different.
While zebras chew away at ground roughage, ostriches selectively nip buds and succulent shoots; the most nutritious portions. Thus, these foragers are no competition to each other.
The hoatzin is a pheasant-sized tropical South American bird with a large spiky crest; looking like an unkempt chicken that lives off the leaves of forest trees. While an ostrich ferments its cellulose in a cecum, like a horse, the hoatzin has a rumen: the only such bird. Foregut digesters are prone to belch microbe-generated methane (from digestive methanogens), as does a hoatzin. Hence hoatzin smell like cows.
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Like forest fruit, many plants on the plains only grow when it rains. This turns many dry-land plant eaters into opportunistic nomads.
African queleas, a small weaver bird, move in vast flocks, following the rains. A single colony may be tens of thousands to millions of pairs of birds. Humans consider queleas a pest, and so have tried to eradicate them with poisons, napalm, and pathogens, but have gotten the best results by dynamiting the dense colonies.
Quails in Africa and Asia forage likewise, though not in such prodigious numbers, nor to such human annoyance and mass murder.
Emus
Like ostriches, Australian emus live in dry open spaces, foraging on the tastiest parts of plants, along with small-animal supplement, chiefly insects.
Plentiful pickings are found only after rainfall. They gorge on abundant food, fattening up to 45 kilos, as well as drinking their fill. When the food runs out, emus trek in search of rain.
Emus can travel long distances at a fast, economical trot: with strides up to 275 centimeters, at up to speeds of 50 km/h (kilometers per hour) if necessary, though typically hiking at a steady 7 km/h for hundreds of kilometers at a stretch. Emu legs are among the strongest of any animal.
A trek is metabolically expensive. An emu may lose half its weight, down to 20 kg, from one feast to the next.
Emus have a good sense of smell, fine hearing, and excellent eyesight. Like vultures, they go toward clouds. Emus especially trek toward thunder, in hopes of green grazing.
When food is plentiful, emus are none too social. They avoid each other. But once on the hunt, emus hike in great herds. As they meet, in traveling from one region to the next, new recruits join. 70,000 birds may march together to the next feast. Once at the feeding grounds, emus disperse until the next trek.
Australian farmers have all the regard for emus that the ancient Egyptians had for locusts. They try to thwart a trek by putting up long (up to 1,000 km) fences. Similar fences are built to keep out kangaroos and rabbits.
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Plants resist being eaten by stuffing their otherwise tasty bits with toxins. Some animals overcome that by harboring microbes which can cope with the toxins, as well as having a well-equipped liver.
Hoatzin eat leaves that are toxic to others, though limiting their exposure via variety. So too the wood grouse, the largest of the grouse family, which subsists mostly on pine needles, which are highly fibrous and resinous.
Fruit-bearing plants evolved to favor animals that are good seed dispersers. Monkeys tend to pillage, stripping trees of fruit, then eating in situ; very little dispersal.
Birds are better dispersers. Macaws eat a variety of fruits and succulent plant parts, many of which have toxins. Macaws compensate by eating a specific clay off cliffs which sufficiently neutralizes the toxins.
African turacos forage for fruit in bands of up to a dozen. These excellent seed dispersers can eat berries that are positively toxic to other species. 80% of the eaten seeds pass through, unencumbered from future growth prospects. Thus, the berry bearers ensure that turacos alone feed on their fruit.
Turacos are also unusual in feeding their infant chicks fruit, although infant diets are supplemented with tasty invertebrates, including snails.
Plants that seek the help of pollinators provide protein-rich pollen in return for spreading it around. It’s a start. But bribing butterflies, bees, birds, and bats necessitates nectar, a rich sugar solution produced for no other purpose.
Hummingbirds
Most nectar feeders are passerines, but a few are not, including the most famous: hummingbirds. Nectar, the mainstay of the hummingbird diet, is topped off with protein from pollen and tiny invertebrates, typically caught on the fly.
Using extraordinary long tongues tucked into a long slender beak for protection, a hummingbird plumbs the depths of deep-tubed flowers; typically, a 1,000–2,000 flowers per day.
To procure flower nectar, a hummingbird tongue curls into a sealed cylinder, owing to surface tension. Nectar is drawn upwards, filling the drinking-straw-like cylinder.
The hummingbird withdraws its tongue, scrapes it clean, and swallows. This extraction process is repeated 20 times a second as a hummingbird feeds.
A hummingbird defends its flower patch as if its life depends upon it, which it does. Hummingbirds and their specialist flowers are a lovely example of coevolution.
Hummingbirds have an optimal fuel-use strategy that powers their high-energy lifestyle, maximizes fat storage, and minimizes unnecessary weight gain, all at the same time. ~ American zoologist Kenneth Welch
Hummingbird metabolism is marvel of evolutionary engineering. Hummingbirds are the only vertebrate that can use fructose, as well as glucose, to power themselves. For other animals, fructose metabolism is inefficient.
Consuming so much sugar in solution requires relatively prodigious quantities of water: up to 160% of body mass each day. Water presents a challenge to almost all birds. Most birds need to keep their weight down, and so cannot afford to take on too much water. Hummingbirds are rare in sucking a surfeit of it. Whereas most birds conscientiously conserve water, hummingbirds evolved to get rid of it. Hummingbird kidneys are adapted to produce very dilute urine, which they spray as they go.
Finding watering spots can be non-trivial to life on the wing. Some avian lives are built around the need to drink. The feeding and watering of chicks certainly shapes the lifestyle of all birds that care for their young.
Passerine nectar feeders generally perch alongside the flowers they feed upon by gripping the stem with their strong feet. Contrastingly, hummingbirds hover. More controlled then even kestrels or terns, hummingbirds are among the finest hoverers. Like dragonflies, hummingbird wings move horizontally in figure-8 form.
A slight twitch in pitch moves a hummingbird in any desired direction. Flight feathers move and change wing area as they are flapping to effect optimal efficiency.
Hummingbirds are the only bird that can fly backward. They can do so nearly as efficiently as flying forward, albeit no faster than 16 km/hr. Hummingbirds can even fly upside down.
The smaller the bird, the faster the flap. The 18–24 gram (21.5 cm) giant hummingbird flaps its wings at 10 to 15 beats per second. The 2–6 g (7–9 cm) ruby-throated hummingbird can clock up to 200 beats per second, though its fleetest flying is reserved for courtship displays.
Hovering requires prodigious power. Hummingbird flight muscles account for over 30% of body mass, which is a not-too-significant step up from an average bird.
Hummingbird flight muscles are attached to a long sternum which is deeply keeled, supported by 8 pairs of ribs; 2 more than most birds, to better distribute torsional stress. Special shoulder joints allow all-around movement. Very few animals, primates excepted, can move their forelimbs with such versatility.
A key facet of hummingbird strength is the wing aspect ratio. During a down stroke, wings with a larger aspect ratio use significantly less power than wings with smaller aspect ratios.
Hummingbirds have a length-to-width aspect ratio of 3.5 to 4.0 – able to deliver the most power economically, and optimal in the trade-offs between power, energy consumption, sustained flight, and flight versatility.
Hummingbird flight is an engineering marvel. As a hummingbird pulls its wings forward and down, tiny wind vortices form over the leading and trailing edges of the wings. These vortices then merge into a single large vortex, forming a low-pressure area that provides lift. Hummingbirds further enhance lift by pitching their wings upward as they flap.
Large birds generate all of their lift on the downstroke. They pull their wings in toward their bodies to reduce the drag they produce while flapping upward.
Hummingbirds uniquely generate lift on the upstroke by inverting their wings. As the leading edge begins moving backward, the wing rotates so that the top of the wing becomes the bottom and the bottom becomes the top. This allows the wing to form a leading-edge vortex as it moves backward, generating lift.
The upstroke produces 30% as much lift as the downstroke. But the upstroke takes only 30% as much energy, making the upstroke as aerodynamically efficient as the more powerful downstroke.
Like hummingbirds, flying insects – dragonflies, houseflies, and mosquitoes – can hover, dart forward, backward, and side-to-side. Despite structural differences in their wings, both similarly power their flight using vortices to optimize efficiency.
Hummingbird flight is more like that of insects than other birds. Both flying insects and hummingbirds can produce positive lift on both the downstroke and upstroke. The parallels of hummingbird and insect flight exmplify convergent evolution.
Convergent evolution is the independent evolution of similar traits in unrelated organisms. Convergent evolution illustrates a natural path of adaptive solutions given various trade-offs in biomechanics or biochemistry.
Powering hummingbird flight muscles at pace means maximal metabolism, the highest of any vertebrate: 400 times that of a human (energy per body weight).
Respiration is commensurate. Hummingbird oxygen throughput is the highest of any vertebrate: twice that of shrews, the smallest mammal. A hummingbird at rest takes 300 breaths per minute; 500 in flight.
In addition to lungs, all modern birds have supplementary air sacs. Hummingbirds have 9 such sacs.
The tiny birds’ energy expenditure produces prodigious heat. Hummingbirds do not waste energy keeping themselves warm when not exerting themselves feeding. Instead, they can enter a state of torpor; an adaptive trick highly unusual among birds. Body temperature drops to that of surroundings. Hummingbirds at high latitudes tend to torpor during cool nights, saving ~60% of their energy in that state.
There is a downside to the economy of torpor. Torpid animals are easy prey.
Senses
Despite having beaks, many birds have a fine sense of smell. Honeyguides are led by the nose in finding bee hives. Vultures detect rotting carrion from the air with their well-honed sense of smell.
So too the avian sense of taste, which is adapted to eating habits. Hummingbirds can taste the sugar concentration in nectar.
Bird sight and hearing are typically quite acute. Such sensory acuity also highlights that the pace of avian existence is many times that of longer-lived and slower animals such as humans.
Sight
Birds are super visual. They have excellent color vision and good visual acuity. ~ American ethologist Tricia Rubi
Flight is mentally demanding. There is a continual flood of visual information that comes in during flight, integrated into a memory-based mapping system.
The mental processing demands of flight are heightened by the fact that birds have excellent eyesight. This is partly achieved by exceptionally large eyes. A bird’s eye may be larger than a much bigger mammal. A 200-gram owl has a larger set of peepers than a 100-kg human.
The eye of the ostrich is the largest of any terrestrial vertebrate. It approaches the upper limit of optical effectiveness in a biological structure.
Predatory birds generally have relatively larger eyes than other birds. Because a larger eye offers better resolution, a hawk can see a sparrow at a much greater distance than a sparrow can see another bird its own size.
How a bird sees depends on the position of its eyes and the shape of its head. Barn owls have flat faces and forward-looking eyes, yielding very wide binocular vision. By contrast, seabirds such as terns, and most passerines, have a narrow field of binocular vision, but impressively wide peripheral vision. Other birds, such as parrots, with eyes toward the front of round heads, have both broad binocular vision and wide peripheral vision.
The fovea is the portion of the eye with sharpest vision, as it has the highest concentration of photoreceptors. Most animals, including humans, have a single fovea in each eye.
Falcons and other birds of prey have 2 foveae per eye, affording greater visual acuity. Hummingbirds – who hunt flowers – move so fast that they too have 2 foveae, to match their bodily speed with vision ability.
1 fovea, as with other animals, provides good eyesight up close. The 2nd fovea acts as a telephoto lens, providing excellent distance vision.
Bird fovea are adapted to their lifestyle. Many seabirds have fovea that help detect horizons.
Bird eyes have a structure that other animals lack: a pecten oculi. This comb-like pecten sticks out like a large finger from the rear of the eye.
While the pecten oculi appears as if it would obstruct vision, it is cunningly positioned over the eye’s blind spot. The pecten is a blood vessel complex that provides extra nourishment to the eye, as well as helping protect it from damage from ultraviolet light.
Color is important in recognizing things, but it does not help nearly as much in flight or landing as edge detection. Quickly detecting contrasting edges is crucial to all animal navigation, but particularly so for fliers, and especially in low-light conditions.
Birds can see red, green, blue, and ultraviolet. Their critical edge-detection acumen is color-blind, which means it works well under any lighted condition.
Hearing
Like many reptiles and dinosaurs, birds have no external ears: only a narrow opening leading to the inner ear. Yet avian sense of hearing is typically keen.
Bird skulls act to conduct and transform sound in ways that afford highly accurate hearing from any direction. It is an intricate evolutionary adaptation.
Leaving off ears allows better sight. Eye placement on the side of the head gives birds a wide field of vision.
Some birds of prey, such as owls, have a different arrangement of eyes and ears which afford specialized capabilities. Diving birds have strong protective feathers to shield their ears from the water. During deep dives, they close the outer ear by folding the enlarged rim of their external ear.
Humans perceive sounds via relative pitch. This lets us hear a tune in one octave and recognize it played in a different octave.
Birds cannot do this. Birds hear in absolute pitch. Birds do recognize timbre: a fundamental note combined with harmonies.
Birds can hear much shorter notes than humans. A human can hear a sound 1/20th of a second long. Birds can discriminate a sound up to 1/200th of a second. What we hear as a single note may be 10 separate notes to a bird.
Many birds have a hearing range comparable to humans. The greatest sensitivity is typically between 2,000–4,000 hertz. Some birds have much more perceptive hearing.
Owls
Owls are sensitive to whisper-soft sounds, thanks to a profusion of hair cells in their exceptionally large cochlea (inner ear cavity).
Further, the flattened and pie-shaped faces of owls serve as a sound-gathering disk, passing percussion to the ears via stiff, specialized features on the disk’s circumference.
Owls also have asymmetrical ears. One ear is lower on the skull than the other, which means that sounds from a lone source reach the ears at slightly different times. This gives an owl the equivalent of binocular hearing, allowing them to pinpoint the source of a sound with tremendous positional accuracy.
So much of the lateral real estate of an owl’s skull is taken up by its ears, with frontal sculpting to optimize sound reception, that the only place left to position eyes is the middle of its face. Despite that, owls have surprising peripheral vision.
Seasonal Changes
Living in temperate zones means significant seasonal changes. Food becomes scarce in winter.
Ideally, an animal’s energy consumption would fluctuate to meet its needs and accommodate food availability by economizing during lean times. Birds do. Regulated by hormones, avian internal organs undergo enormous seasonal changes.
Male gonads shrink outside of mating season. During the winter, a male sparrow’s testes are no bigger than a pinhead. By the time breeding season is upon him, the sparrow’s testes have swelled to the size of a baked bean.
Similar seasonal changes happen to females. An oviduct is a mere thread of tissue in winter. By the breeding season, an oviduct has become a massively muscular egg-delivery tube.
Temperate birds sing in the spring, defending territory and wooing a mate. The hearing ability of songbirds is at its best when song is most important.
Humans also have regulated changes in hearing ability; or, at least, females do. When estrogen levels are high, a woman is fertile. During this time, a man’s voice sounds richer, even though most women are unaware of the subtle change.
The brain is an expensive organ to run. The human brain consumes 10 times the energy of other organs. So too with birds. Their brains economize and enlarge along with sensory needs, which have a seasonal aspect.
Brains & Intelligence
There’s been a bias against birds because they have small brains. ~ American cognitive zoologist Thomas Zentall
Avian brains are uniquely organized: quite different from simians, who have an extensive cerebral cortex. (The radically different structure of avian brains from mammals illustrates both convergent evolution and that brains are merely a physical facsimile for intelligence, which is functionally housed in the immaterial mind. The body is ultimately an energetic construct.)
The intelligence system of birds evolved early in their descent, in anticipation of taking wing. Requirements for high-speed vision processing and muscular coordination for flight drove avian evolution. The bird brain is an artifact of those demands.
Proprioception in birds is superlative. The ability to quickly fly amid trees and in tightly woven flocks requires an exquisite sense of instant body width.
Birds do not have a cerebral cortex. Instead, an avian brain has a hyperpallium. The hyperpallium is cladistically new in birds.
Cladistics classifies species into groups (clades) based upon evolutionary lineage. In other words, cladistics defines branches of descent in the tree of life.
Birds have been evolving on a separate tract from mammals for 300 million years. Despite the extensive structural distinctions between bird and mammalian brains, the working of avian and mammal minds is selfsame. Avian long-term memory and problem-solving is equivalent or superior to mammals.
Bird brains show how intelligent behavior is produced with a different anatomy. ~ German neurobiologist Lena Veit
As birds share a close evolutionary heritage with dinosaurs, their brain structure and intelligence are likely to be similar. To this the fossil record leaves many questions.
Chickens
The common chicken is a subspecies of the Red Junglefowl, which was domesticated 5,000 years ago in Asia, then taken around the world for its eggs and meat.
With a global population of over 19 billion, chickens are the most abundant domestic animal. Chickens being a commodity has abetted a human bias: thinking that chickens are stupid. Such is the typical acumen of the human Collective.
Chicken intelligence, self-control, social sophistication, communication, and math skills are on par with primates. Self-control is typically not evident in human children until they are at least 4 years old. Nuanced communication skills comparable to chickens comes even later to youngsters.
As with most, if not all organisms, chickens have distinct personalities. A mother hen has her own personal maternal behaviors which affect her chicks’ upbringing.
Chickens have a large repertoire of visual displays, and at least 2 dozen distinct vocalizations. Chickens use sounds and gestures to convey their interpretations of situations and state their intentions.
Males and females have their own social hierarchies, which are self-enforced without a fuss (the so-called pecking order). A chicken knows its place in the social order, and politely defers accordingly.
Further, a chicken can determine the status of an unknown individual by its interactions with a chicken of known social status. A chicken will thereupon treat the stranger appropriately (dominantly or submissively) in its own future interactions. This reasoning faculty is termed transitive inference.
Dominance is roughly related to size, but top-rung birds are seasoned and wily. As with other such social animals, cliques are common.
In a flock, there is an alpha rooster with mating rights. He happily crows about his prowess.
Finding a mouth-watering morsel that might attract a mate, an alpha rooster will make a dock-dock sound to draw attention, then perform a tidbitting display: rapidly twitching his head side-to-side, bobbing it up and down, then repeatedly picking up and dropping food to signal a female that he has something tasty for her.
In looking after their own self-interest, chickens can be positively devious. A subordinate rooster on the make might lure a hen for an affair by first seeing that he has her looking his way, then performing the tidbitting display, but quietly, so as not to draw the dominant rooster and suffer repercussions.
A chicken takes account of its past experiences and knowledge in making decisions. Chickens can solve complex problems, using deductive reasoning which human children only develop around the age of 7 years. Chickens empathize with individuals in danger, indicating theory of mind.
Chickens consider before they act. A rooster that sees a threat overhead, such as a hawk, might let a female nearby know, but will keep mum if the threat is to a rival male. Or the rooster may call out if he is concealed and his rival is in the open.
A female is equally selective. She may raise an alarm only if she has chicks in her care.
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What cannot be disputed is that birds are certainly not birdbrained in the colloquial sense. Their cognitive abilities are comparable to mammals, including capacity for complex social reasoning.
Not only do birds learn rules well and have brains that would be considered quite respectable in size in a mammal, but they have been reported to make and use tools and to develop rather resourceful strategies for solving problems. ~ American biologist William Hodos
Sociality
Birds become gregarious when flocking increases their chances of survival and facilitates foraging and breeding. The advantage of group living includes early warning of predators, more effective group defense, enhanced ability to find mates and increased foraging efficiency. The old adage that there is “safety in numbers” is particularly true for birds. ~ American ethologist Joanna Burger
Bird sociality ranges from mostly solitary to highly gregarious. Even those given to solitude have social relations, even if limited to pair bonding and territorial interactions.
Tinamous, loons, and some hawks and eagles mostly operate alone or in pairs. Conversely, grackles and blackbirds, herons and egrets, ducks and geese, and gulls and terns, do most everything in groups.
Even within a species there are variations in social behavior patterns. Gray and great blue herons, which typically nest in solitary pairs, may also inhabit nesting colonies of thousands.
In the outback of Australia live chestnut-crowned babblers who live in groups. Most members help take care of young chicks despite not being parents themselves. Some babblers are diligent, while others do little. The industrious ones tend to be caring for brothers and sisters, while the lazy babblers have more distant relatives as charges, if the hatchlings are related at all.
Finch Society
Socialization plays a major role in the life of many birds. Male zebra finches that neglect fraternizing with females during adolescence are less successful at courtship as adults. Such shy, rejected birds are not total losers. They simply court less attractive females. Conversely, socially adroit finches score preferable mates even when they are not physically attractive.
Female house finches prefer males with the reddest feathers. Dull-colored males know they are at a disadvantage. They compensate by being gregarious before mating season. The duller a male, the more likely he is to engage with multiple social groups.
Birds in a social group flock and forage together. Any bird can choose to associate with multiple flocks.
Females have limited options to choose from and this is a way for males to manipulate their chances to find mates, by placing themselves in certain settings. ~ American evolutionary biologist Kevin Oh
Communication
A bird doesn’t sing because it has an answer, it sings because it has a song. ~ American author Maya Angelou
There are only so many ways to get something done, and, by the evolutionary equivalent of Occam’s razor, efficiencies often dictate adaptation. Nature’s fondness for diversity is matched by its affinity for economy. For example, while bird brains and human brains have considerable structural differences, both use grammar in communication construction in a selfsame way.
Birds communicate in a wide variety of ways. At close range, gestures and ritualistic dance are employed.
Earshot has a much wider range than line of sight. Bird sounds are of every sort. Feathers drumming, wings flapping, or beaks hammering are non-vocal ways to make a point, whether staking a territorial claim, acting with alarm, or wooing a potential mate.
Vocalizations are extensively employed. Altogether a profuse variety emanate from different avian species. Clicks, quacks, insect-like buzzes, warbles, whirrs, chirps, and drum solos are a few techniques.
Bird calls are a common coin of communication. Several passerines species are capable of something more: song. A few birds are capable of breathtaking sonic beauty. To a bird, song means much more than notes soaring through the air.
Songs and Such
All birds vocalize using their syrinx, which is a specialized organ only birds possess. Many avian vocalizations are innate, others learned, depending upon species. In this, birds are no different than mammals.
Birds that depend on stealth to stay safe need to be able to signal their chicks to stay still. Such birds all have a call that instantly immobilizes fledglings, which keep quiet until they hear an all-clear signal.
Young cuckoos, reared in the nests of other species, never hear the songs of their parents while growing up. Once they reach adulthood, cuckoos express a lingo they innately know.
A few birds, such as mute swans and turkey vultures, can only hiss and grunt. Others have an unmatched sonic virtuosity. Many birds surpass simians as communicators, possessing vocal abilities far superior to those of humans. Parrots, hummingbirds, bowerbirds, and many songbirds have an uncanny talent for vocal learning: hearing a sound once, then reproducing it.
Avian physiological responses when listening to their songs are selfsame to how people respond to music, indicating that song is a similar emotional experience for both.
Only a small proportion of birds sing at all; many fewer with virtuosity, at least to human ears. It may be that many more appreciate music. Parrots are known to dance to ditties.
Woodpeckers aren’t much in the vocals department, but some create rhythmic jazz by striking hollow trees to create rich staccato calls. They have even learned to amplify their output by drumming on TV antennas or other metal pipes.
A singing bird is making a statement of its life energy: that it is strong, healthy, and has territory to proclaim. An individual’s song complexity and repertoire as an adult reflects its early development, as well as its mental and physical prowess.
Bird song is an honest communication. Hence, song serves well as a surrogate for more physical displays, especially fighting, which would be considerably riskier and taxing than singing to make a point.
As song is often a competitive exercise, males are the vocalists of most songbirds. Testosterone stimulates singing.
Birdsong variability reflects the balances of functions which songs serve in species: declaring territory, repelling rivals, attracting a mate, and so on.
Songs and calls are also used for social cohesion. Northern mallard ducks call at nightfall, to gather together before departing from a foraging location.
Many bird species sing to attract others to a rich feeding site; a practice not unlike the honeybee waggle dance in intent, albeit simpler in information content.
Resident tropical birds have a low turnover, so territorial boundaries tend to be stable. Intrusions into declared properties for sneaky copulations are rare. Singing rates in these tropical birds are relatively low.
For temperate-zone birds, much of a male songbird’s day may be spent singing. A song sparrow sleeps 9 hours, sings 9 hours, and spends the other 6 hours eating and in other pursuits. A Red-eyed vireo may sing 20,000 songs in a day. An adult tropical manakin may spend over 80% of its waking hours singing. A typical migratory songbird, such as the hooded warbler, may sing 30–40% of its day, clocking well over a hundred ditties per hour.
In 71% of songbird species, females also sing, including the red-winged blackbird, Northern cardinal, black-headed grosbeak, and many tropical birds. Some female tropical bush-shrikes and barbets regularly engage in synchronized duets with considerable style. Singing is fun as well as informative.
The female of the common ancestor to birds sang, but female singing has been lost in several songbird lineages, for reasons unknown.
Like males, female song is typically not of welcoming cordiality. In species where a male has multiple mates living in his territory, a resident female benefits from singing by discouraging other females to settle there, as resources would have to be shared.
The bluethroat is exemplary. Males arrive in spring, before females. Complex songs and different displays carve territory and attract mates. A male may be polygynous and attract 2 or more females to nest on his property. Female bluethroats are generally secretive during breeding season, but if they spot another female looking to nest, they will come out to confront the newcomer with songs of dissuasion.
D’Arnaud’s barbet, an African bird, is something of a choral species, led by duetting. These birds live in groups of 3 to 6. There are a dominant male and female.
Throughout the year, though more often during breeding season, the dominant pair practice vocal interplay, with increasingly synchronized precision as time goes on. The male starts it off with a passage, then the female follows with her bit, and so on for several minutes of song. Other group members sporadically join in with accent chirps.
Sometimes a secondary male and female may duet out of earshot of the dominant pair, but competition is not tolerated. Singing serves for bonding, as well as expression of dominance and territorial claim. Determined secondaries strike out on their own.
While singing is intrinsic to many songbirds’ lifestyles, singing is also purposeful in its expression, as shown by the fact that song production decreases following breeding. The prairie warbler doesn’t quit singing with offspring on the way, but he does cut back considerably.
The sedge warbler exhibits impressive virtuosity during courtship, with long and complicated songs; no two ever alike. The more complex the song, the better the odds of mating. Once mated, a male sedge warbler retires his musical muse, forsaking singing entirely.
Not only does song put a shine on a male’s attractiveness; in some species, it stimulates female reproductivity. Female canaries wooed by masterful vocalists build their nests more quickly and lay more eggs than those mated to a singer with a smaller song repertoire. The female ring dove actually needs to hear her mate coo for her to produce eggs.
Birdsongs have a syntax which birds learn by listening to others. Even relatively simple tweets are syntactically replete. For example, while Bengal finches respond to playbacks of native communiqués, remixes that scramble syntax are not acknowledged.
The sophistication of birdsongs varies widely among species. Some bird songs are completely unlearned. Such birds are born with innate tunes. Doves and pigeons are exemplary.
The chipping sparrow has 1 song that it repeats over and over. In contrast, its cousin, the song sparrow, may have 1,000 variations for its 20 songs.
Song sparrow vocal stylings employ rhythm, pitch, and timbre to shape a song. Unlike thrushes, which rapidly rotate through their repertoire, song sparrows repeat songs, mining the groove of a tune with variations.
Many passerine birdsongs are developed constructions from an elaborate learning process: a process that must be rewarding to the singer. Finches have relatively simple songs compared to thrushes, which sing songs of great complexity and beauty: compositions of various elements strung together that may last for several minutes.
Most birdsongs demonstrate an interleaving of inherited and learned components. The frameworks, shown by simple songs, are largely inherited. Learned elements comes from peers, riffs from other bird species, and even non-avian sounds from the environment.
Young singers don’t simply learn their songs by imitating adults. They get feedback by watching their mothers’ reactions to their immature songs. As with human babies learning to talk, avian mothers steer their offsprings’ song development.
A mother guides her baby’s song toward her favorite version. There’s nothing imitative about it. ~ American psychologist Samantha Carouso-Peck
Mockingbirds
Mimus polyglottos is Latin for “many-tongued mimic.” That apt label applies to the mockingbird: a plain-looking bird with extraordinary vocal talent.
In between its own compositions, a mockingbird will throw in replications of others; dozens in a day. Mockingbirds not only sing the songs of other birds, they also blend in the sonics of insects and amphibians: anything that catches their ear as catchy.
Mimicry is not most of a mockingbird song. Only 5–18% is imitative. The rest is original.
Mockingbirds have been heard to sing 200 different songs, though they cannot cover the jazz of song sparrows. Such prolific verbosity gives a vigorous defense of territory, as well as advertising a studliness in song that a female might appreciate in a mate.
Mockingbirds are perceptive in more than just song. They quickly learn exactly what in their environment poses a threat.
Mockingbirds have a keen awareness of different levels of threat posed by individuals of another species. ~ American evolutionary ecologist Douglas Levey et al
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Some birds earliest singing shows a much wider repertoire of elements than they will ever display again, once their song style has developed. Similarly, human infants begin babbling with utterances that incorporate sounds used in every human language.
As language is learned, only those sounds employed in the spoken tongue(s) are retained. Other sounds disappear.
The mental versatility that accompanies bi- or multilingual learning in children is accomplished by having to remember and handle a greater combinatorial variety of sounds mapped to lingual meaning.
The songs of swamp sparrows crystalize similarly: taking on the dialect of the local area. Young birds begin with sub-songs that sample the whole range of the species’ repertoire. Taking their cues from nearby adults, the elements are pared to fit the local dialect.
Variation is also a byproduct of habitat. Songbirds that live with fluctuating weather tend to be more flexible singers. Versatility in volume, pitch, and tempo facilitate adjusting for local conditions, to best get the song across to its potential audience.
Sound transmits differently through diverse types of vegetation. Further, the fullness of vegetation varies with precipitation.
When birds first arrive at their breeding grounds in the spring, the trees bear few leaves. Within weeks, as the leaves come in, fed by spring rains, sound transmission changes dramatically. Songbirds adjust accordingly.
Singing in the City
Urban birds must deal with the din that pervades human habitats. Even the suburbs raise a racket.
Birds change their songs so that their notes are not masked by human noise. They may raise the volume, alter pace, shift to a higher frequency, and/or sing at a quieter time of the day.
Traffic and city sounds tend to be low frequency rumblings. To compensate, European great tits have eliminated low frequency syllables from their songs that would otherwise not be audible. They also sing shorter songs and compose differently: singing song forms not found in forest populations.
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Singing is symptomatic of sociality. Many songbirds have individual songs and styles. Many songbirds recognize a neighbor by his signature style. Birds reply in song to one another based upon previous social interactions with each other.
The songs of adjacent territory holders have overlapping elements and individual stylistic distinctions. The songs of neighbors with whom a bird has no boundary disputes tends to be ignored, but a new variant attracts a rapid response.
Songs vary in their aggressive intent. Some songs are reserved as harsh language.
Adult Adélie penguins call to their young as they return from sea with a meal. The young come running, calling back.
Before serving food, penguin parents and chicks engage in an identifying fest of call and response. Chicks who approach an adult that is not its parent are driven away. Parents may be able to identify their chicks by sight, but chicks do not respond to silent adults.
Dark-eyed juncos are a small, grayish sparrow common in North American forests. Junco males have loud territorial songs, but also soft, complex tunes that they sing in courtship. If one junco male hears another singing loudly, the territorial marking is often ignored. But if the song overheard is whispered anywhere near its territory, it prompts an aggressive response, as it suspects that another male is trying to woo his mate.
The song sparrow mocks intruders by mimicking elements of their songs, as a way of telling the interloper that it is being watched, and to watch itself. Song sharing often leads to a fight, so this is more than an idle taunt. This threat is real enough that young sparrows don’t dare mock their elders. Song taunting is only done by tough old birds.
For cowbirds, the local dialect is not just a product of territorial males. For snatches of the right song, females respond to male singing by inviting displays: a rapid shuffling of the wings similar to copulation invitation. This enticing signal is displayed by numerous passerine species. Such encouragement tends to tailor a male’s song to the dialect where the female is from. Thus, an attractive female’s preference for her native dialect modifies the songs sung by local males.
Local dialects are somewhat typical for virtuosic songbirds. This is to be expected, both for song composition and style, as singing is largely a learned behavior from local conditions, and as song is an expression of sociality. For more rote singers, dialects are less distinctive, if they even exist.
A distinction may be made between emulation and imitation. Copying how objects are manipulated is emulation, while learning from demonstration is imitation.
Imitation is generally considered a sign of a higher cognition. This is a human bias, as humans are so socially oriented as to find imitation sometimes easier than emulation.
For example, assembling furniture by direction is emulation, while watching someone do it, then performing, is imitation. Humans oftentimes struggle following directions but perform aptly more quickly by imitation.
European starlings are startling vocal mimics. But they also learn from watching others. This is imitation.
In experiments carefully designed to differentiate between emulation and imitation, budgies demonstrated imitation. Japanese quail socially learn. They are imitators.
Parrots are known for mimicking human speech. African gray parrots understand the human language they learn, including context. Parrots lack lips and teeth, but they have a tongue which they use to form sounds in the same way that humans vocalize.
The unique vocal organ of songbirds is a more complex instrument than the human larynx and vocal cords, which sits high in the throat. The avian syrinx is located at the lower end of the windpipe. The syrinx produces sounds by air flow through vibrating membranes: their shape and tension modulated by a sizable number of small muscles.
This arrangement gives songbirds tremendous innate versatility, including fine pitch control, and the ability to produce 3 or 4 complex sounds simultaneously. Some species of songbird can control the 2 sides of their syrinx independently, allowing them to sing 2 melodies (point and counterpoint) simultaneously. By contrast, humans achieve sound variability by vocal tract filtering.
Birds can transmit and receive vocal messages 10 times as fast as humans. While birds see in a broader visual color spectrum than humans, both hear in the same frequency range. But birds discriminate sounds much more quickly. Whereas a human hears a single note, a bird may hear 3 rapid tones, or even more.
The physiological limits of human hearing and cultural inclinations codified their sound of music, most of which is based on variations of only 5 to 12 notes. The 12-note chromatic scale characterizes most Western music, and the 7-note diatonic scale is used in most popular music. The 5-note pentatonic scale was used in ancient Greece, is common in Eastern music, and predominates nearly every riff played on the electric guitar.
Bird songs are composed on more complex scales, with different harmonic intervals. Birds sing discrete notes in clear tones and repeat similar phrases. That is about as far as human music resembles bird song. Birds possess a vividly richer sonic tableau and corresponding cognitive sophistication.
Bat Song
Bats have the same degree of vocal flexibility as songbirds. ~ American neuroethologist Cynthia Moss
Some bats sing complex songs every bit as intricate as the most florid birds. Like songbirds, sophisticated bat repertoires are not innate, but learned. Each bat species has a distinct style and techniques, as well as individuals having their own flourishes.
Selfsame to songbirds, bat songs are sung for territory and to lure mates. Unlike many birds, which have a single, dual-function song for both territory and mating, bats sing distinct songs for the 2 purposes.
Most birds have only a short developmental period during which they learn songs. By contrast, adult bats, like the most sophisticated bird singers, can learn new tunes.
Bat songs have social implications beyond bird usage. Bats profusely sing when in residing in an all-male roost with a million other guys. Bats just love to sing.
They’re peeing on everything, marking every bit of their territories. And just singing their hearts out. ~ American ethologist Kirsten Bohn
Parrots
African gray parrots are highly social: living and foraging in large flocks. These parrots are renowned for their intelligence and longevity.
Parrots live in fission-fusion flocks, like the socially-fluid groups that dolphins live in. For parrots, imitation is the sincerest form of flattery.
A parrot may mimic another to start a conversation. Each parrot has a distinct contact call that serves as an audible name.
While chatting, parrots often invoke phrases that mimic their conversation partner. This imitation is like the human tendency toward mimicry to indicate comity. Dolphins also mimic for the same reason.
Alex
One researcher’s pet parrot, Alex, was bought in a shop when he was 1 year old. Alex was taught English for 30 years.
Alex had a vocabulary of over 150 words, and it was clear that Alex understood what he was talking about, including symbolic representation, such as relative size and color.
Alex knew the difference between cardinal and ordinal numbers. He also identified zero as “none.”
Alex could identify over 80 objects, 7 colors, 5 abstract shapes, and numerous materials. If asked to identify the difference between 2 identical objects, Alex would reply: “none.”
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The capacity to learn by associating sounds with meaning makes sense biologically. ~ English ethologist Andrew Radford
Numerous birds listen to the communications of other birds, including other species, including their predators. Ground-nesting birds, such as the ovenbird and veery, avoid putting their homes in the territories of bird-egg-eating chipmunks. They do so by listening for chipmunk sounds nearby.
Siberian jays tell other members of their group what a predator is doing, with different calls to inform whether a hawk is sitting, patrolling for prey, or attacking. Recipients respond accordingly.
For birds given to song, their music is often a cultural transmission. Other cultural transfers exist, though many are not as easily observed. The showmanship of bowerbirds – with their elaborate mating bowers and courtship ritual of song and dance – is an extravagant exception. Bowerbirds can accurately mimic a whole soundscape.
I heard a bowerbird mimicking an entire audio scene with the most astonishing accuracy. I was amazed… shocked. It’s by far the most impressive piece of vocal mimicry I’ve ever heard. ~ American ornithologist Gerald Borgia
Female bowerbirds prefer to mate with the most talented, accurate mimics. Vocal mimicry more closely relates to mating success than the artiness of the bower structures which these birds are best known for.
Foraging Guidance
Exploiting new food sources is a common problem for social animals. Communication to locate and exploit rich sources is immensely helpful.
Social insects are known to share such information by symbolic communication: using various means, including gestures, to indicate direction and distance.
Insectivorous bird parents feeding a nestful of hatchlings take turns foraging. If one parent finds an abundant aggregation of edible insects some distance from the nest, does it tell the other? The fitness benefit would be considerable. So, it seems likely. But that question remains unanswered, because reliably recorded human observation has not been made.
Honeyguides
The honeyguide is an arboreal near passerine, with separate species native to Africa and the Indian subcontinent. A honeyguide has an ironic lifecycle: a vicious beginning, leading to solicitously seeking cooperation from other species to feed.
Honeyguides are brood parasites: laying their eggs in the underground nest of another bee-eating bird species, to be reared by adopting parents. An adult gives it offspring a head start by incubating its egg for a day before placing it in another’s nest. When placing her own in, an adult honeyguide punctures any other eggs already laid by the host.
In case mom did not do the trick, a honeyguide is born with a needle-sharp beak which it uses to peck the other non-honeyguide hatchlings to death. After a month of care by adoptive parents, a chick loses its menacing beak and leaves the nest.
Honeyguides feed on insects, including the eggs and larvae of bees. They are quite fond of honey and are among the few birds that feed on beeswax.
But honeyguides cannot open beehives. So, they earn their name by guiding other species to bees’ nests they have found, and take their reward after the guided one has broken in.
One cohort is the honey badger (ratel), which, while a badger, looks more like a weasel. The ratel is primarily carnivorous, taking any sort of animal food to be had: birds, small rodents, frogs, lizards, and snakes, even carrion, but will eat fruit and vegetables, such as berries, roots, and bulbs. A honey badger can also be persuaded to bust open a beehive.
A honeyguide will attract a ratel by imitating its grunting sounds or hacking on a tree to simulate the sound of a bees’ nest being ripped open. A honeybird can be quite solicitous, spending up to a half hour trying to cajole a follower.
Having gotten attention, a honeyguide leads the animal on to a known beehive with inconstant maneuvers: flying within 4.5 meters, churring rapidly, fanning its tail and ruffling its wings to signal intent.
Honeyguides have been variously observed attempting to lead a mongoose, monkey, and baboon, but only baboons have been seen following the bird.
In many areas of Africa, the honeyguide is well known for leading human searchers to a honey trove. It is a relationship that may be over a million years old. Honeyguides advertise their readiness to scout to the Yao people of northern Mozambique by flying up close and churring.
Conversely, a Yao may recruit a honeyguide with a distinctive vocalization: a firmly trilled “brrr” concluded with a grunted “hmm.” No other aural sequence is taken seriously by a honeyguide.
Honeyguides recognize the specific information content in the signal. It’s not simply a cue to human presence. It’s a signal that the person will be a good collaborator. ~ English ethologist Claire Spottiswoode
Honeyguides make a big difference to a Yao hunting honey. Left to his own devices, a tribesman finds a beehive just 17% of the time. With a honeyguide, the success rate climbs to 54%.
Honeyguides provide the information and get the wax. Humans provide the skills and get the honey. ~ Claire Spottiswoode
Territory
Territory may serve several purposes and means different things to different birds. For songbirds, woodpeckers, and birds of prey, territory is for courtship, nesting, and feeding. Seabirds, swallows, and swifts use territory for mating and nesting, but forage in undefended areas. Other birds, including bee-eaters and oystercatchers, have distinct territories for mating/breeding and foraging.
The size and nature of territories varies considerably. Birds typically take as much territory as they can defend. Generally, a larger bird takes more territory than a smaller one. The food supply is a significant determinant of territory size, as is competition for available space.
Territories are taken by announcement: singing or otherwise making one’s presence felt. A male ptarmigan makes display flights around his boundaries to put potential adversaries on notice that he is ready to defend his stake. Such displays are typical.
Also typical are border squabbles among neighbors when territories are being established. These lessen in time to more neighborly tolerance.
A territory is not necessarily a locale. South American antbirds eat in the wake of army ants on the march, feasting on the insects flushed out. The dominant birds of the flock take the best spots.
A mobile territory means something entirely different for a brown-headed cowbird or rosy finch. A male follows a female around, trying to defend her from the amorous onslaught of other males.
Advantages
There are several advantages to home ownership: primarily a food supply is secured.
Homeless birds are forced to pilfer – a risky lifestyle. Otherwise, a bird without territory is pushed into a marginal habitat, which demands continual foraging to survive.
The owner of property familiarizes himself with his land; learning the best foraging spots, supply stores for nest materials, escape routes, and other necessities for a prosperous life.
A fine homestead often leads to reproductive success. In some species, territorial claim is a psychological necessity to successful breeding.
A study found that savanna sparrows with less than 600 square meters of home to call their own fared poorly as breeders. Only 11% had nests, compared to over 55% of those with territory over 600 m2.
More generally, a bird with territory confidently comes into his own. Birds without claim to land are meeker. Their song is of the blues: softer, and less proud.
That birds get attached to their territory is obvious, and most apparent by migrating birds that return to the same spot year after year. In one study, 76% of common terns on Cape Cod came back to the same nest site every year. An African bulbul was seen at the same site where it had been banded 20 years before.
Attachment can be more sentimental than sensible. An island once populated with a huge colony of Artic terns became overgrown with shrubs; so much so that it was no longer a suitable nesting site. Yet a few of the oldest terns refused to leave, nesting in terrain that typically would not be tolerated.
Defense
Vigilant defense is the price paid for holding onto a homestead. However vigorously a bird makes clear that intruders are subject to attack, such persistence is paid in kind with retreat and return within minutes.
Birds are terrific trespassers. Encroachment is constant. The finer the property, the worse the problem.
Some birds allow help to hold their claim. Typically, a younger bird is tolerated: letting the hired beak have a place to roost and forage in return for thwarting incursions.
A mated Florida scrub jay readily shares his territory with up to 6 unmated jays, all of whom help in the property’s defense. The area belongs to the mated pair and any offspring, who may inherit the property.
Sometimes groups defend territory, such as with the white-fronted bee-eater, a group of which will claim several square kilometers of foraging territory.
The territories of colonial birds are necessarily constricted: just one to a few meters at most. Group defense is a norm for colonials. Australian noisy miners are not above killing an interloper into their territory.
Group defense is commonly by birds of the same species, though exceptions exist.
The level of effort for defense is variable, and seasonal. Breeding season brings vigor in defense. Many resident birds, including mockingbirds and cardinals, sing more often when fledglings are becoming independent and dispersing, as this is the time when local population is at its peak. Better to not let anyone get any ideas.
Some birds appear fearless in their ferocity, especially species that are fast fliers and adept at aerial maneuvers. Birds of prey, terns, swans, cranes, and magpies fall into this category. Such aviators don’t hesitate to take on threatening creatures several times their size.
If food supply becomes abundant, which typically is a short-lived phenomenon, vigilance gives way to gorging, both by the property owner and intruders. Conversely, in times of scarcity, territory may give way to getting enough to eat.
Pied Wagtails
A pied wagtail spends many of his waking hours defending his property from fall until early spring. If food is particularly plentiful, a chase is not worth the trouble. Sometimes a wagtail strikes a practical compromise: letting another wagtail forage in return for security service.
One study found that a wagtail owner alone immediately spotted 60% of the intruders; the other 40% snatched a snack before being chased off. With a satellite, the instant hit rate went to 85%; only 15% grabbed a bite.
With sufficient supply a territory owner could up his feeding rate by 1/3rd by having a satellite helper: more than compensating for the satellite’s wages. When food becomes scarce – not enough for 2 birds – wagtails aggressively evict their satellites.
In a season of severe shortage, a different scenario ensues. A wagtail temporarily deserts his home, joining a flock to forage. He periodically checks his property, for an improved supply of the insects he eats, and to prevent another bird from moving in.
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The most common method of seeing an intruder off is song. Alternately, or in addition, posturing and chase are employed. Such displays, including flight patterns, are specific to territory defense. To settle a border wrangle, 2 male hazel grouse might chase each other airborne for a while, then run side by side for as long as 45 minutes. The dispute is settled via stamina.
Physical combat to defend territory is not quite common, but it is also not especially unusual. Vocalizations and displays evolved to show fitness for battle, thus lessening the frequency of physicality.
If battle does break out, it is typically vicious. Property is often a deed to a decent life: worth fighting for at all cost.
A penguin will defend its nest site by banging an intruder with its flippers, along with jabbing and biting with its sharp beak. Both fighters are likely to get bloodied. On rare occasion, two equally matched males will fight to the death over a patch of land.
An especially brutal brawl was seen between 2 European robins. In the fight finale, one bird killed the other. Adrenalized, the victor continued to peck at the corpse, taking out its eyes and puncturing the skull. Then it sat for a while, perched high in a tree, and sang its sweetest song. Whereupon it flew down and went back to mutilating its fallen foe.
Battles in Epping Forest
To the victor belong the spoils. ~ American politician William Learned Marcy
The violence of territorial defense varies, even within a single species. Male English robins see off intruders with song if they can. If not, aggressive negotiation may be pursued.
One English robin, keeper of a fine patch of land, was put on alert by a rival, perched high in a tree in the middle of the owner’s territory, who loudly proclaimed in song that new management was taking over. The owner retorted with his own song.
The newcomer flew to a nearby tree, with the unwilling host in hot pursuit. Another new song / old song contest ensued. And so on for 2 days, throughout the property. The intruder’s siege wore the owner down.
After 2 days, the tired old owner ceased his chase. His song grew softer, until it finally ceased. He shortly thereafter abandoned his land as the new owner took possession.
Another eviction came to blows, for the prize was more than territory. An unmated English robin male invaded his next-door neighbor’s property. The intruded-upon was a male with a mate.
The newcomer burst into loud song, with equally fervent response. After a few rounds of raucous songs, things got ugly. The intruder started furiously pecking the mated male. The 2 birds grappled with claws and beaks in physical combat. After 2 hours of battle, the old owner was much the worse for wear, while the intruder was ready to keep on.
The ailing bird fled the attacker to sit on a high branch and sing a soft, forlorn song. Meanwhile, the land’s new lord sang loudly, flying from tree to tree, establishing the new limits to his domain.
The defeated bird hung around a few days, singing softly, occasionally harassed by the new master. The despondent robin then flew off, never to return.
The hen mated to the old owner remained aloof during the conflict. But she lost no time making her presence felt with the victorious bird, following him about with interest. She later mated with him and reared a brood of chicks.
Planning & Memory
Memory for ‘what’ and ‘where’ is not that remarkable in the animal kingdom. Even insects can do it. It is the ability to remember what, where and also when an event occurred – referred to as episodic memory – that is generally considered to be a much more sophisticated form of memory and is usually assumed to be uniquely human. ~ English science writer Helen Phillips
Several bird species make an impressive show of caching food in anticipation of lean winter months; demonstrating planning, and rather incredible memory, in remembering literally many thousands of locations where they have stashed their goods.
Scrub Jay Caching
There are 6 species of scrub jay. Scrub jays plan: seasonally caching food so that they have sufficient supplies with nutritional variety.
The Florida scrub jay’s favorite food is fresh wax worms (wax moth larvae). Alas, wax worms are more perishable than seeds and nuts.
These jays learn how long a wax worm can be stored and still be edible. They retrieve cached wax worms within their decay expiration date or not at all.
Scrub jays watch where other jays cache food and later steal it. Jays tend to steal from those of lesser social standing. They re-hide their own food if they think there is the possibility of it being stolen.
Jays that have not taken to thieving ways are less likely to recache food than larcenous birds. Projecting its own state of mind, a thief is suspicious of others.
Bivouac Checking
Tropical insectivorous birds are presented an instant feast if they chance upon a colony of army ants during a raid, as the ants drive out ahead of them other insects fearing for their lives. Some birds are smart enough to take chance out of the equation.
The white-whiskered puffbird is one such sharpie. These birds practice bivouac checking: auditing army ant bivouacs at the end of the day, after the ants have fed on a raid.
Army ants regularly alternate high and low raiding activity. Birds monitor the bivouacs of multiple army ant colonies, keeping track of the various colonies’ activity cycle, anticipating when a colony will launch a major raid. This allows them to track the colonies through time, as well as take advantage of the spoils from a colony on the march.
The birds do this even when not hungry, demonstrating planning for the future. Colony tracking requires mental time travel: remembering previous activity patterns and anticipating and planning for future events. Mental time travel has long been considered a mental facility unique to humans.
Corvids
Crows are amazing birds. They’re smart, crafty, emotional, inquisitive, and wise, and form complex social relationships with other crows and a wide variety of other animals, including humans. ~ American ethologist Marc Bekoff
The corvid family has over 120 species, including crows, magpies, jackdaws, jays, nutcrackers, rooks, and ravens. Corvids are renowned for their cunning and creativity, as well as their mischievousness.
Corvids mimic human voices and enjoy the confusion they create. Magpies kept by Indian zookeeper Gerald Durrell learned to imitate his maid’s calling the chickens to be fed. When the magpies got bored, they called the chickens, who came running.
Disappointed at not finding food, the chickens went back to roost. The magpies would roust them again with another call. The chickens fell for the ruse every time.
To talk, crows must be able to form and replay memories. Crows manipulate, deceive, play, and converse with other species. They
Intelligence & Awareness
Corvids recognize faces and remember past interactions with individuals, whether of their own species or others, such as people. They also remember conspecific group affiliations: for themselves and the groups to which others belong.
Ravens have mental representations about others. ~Dutch zoologist Jorg Massen
Crows learn from one another in a way that demonstrates their possessing empathic theory of mind.
It’s one thing to learn from one’s own experience, and another to observe that happening to other individuals and infer it happening to you. ~ John Marzluff
Ravens are positively political. Ravens create dominance hierarchies within a group and among groups. They do so by forming coalitions. The benefits of social climbing include better mating privileges, mutual protection, and shared food sources. Like many mammals and some other birds, corvids have a sense of fairness.
Ravens are able to tell where another raven is in its group hierarchy by observing its behaviors with others (transitive inference).
Power may be obtained not only by brute force but also by social strategies resembling human politics. ~ Jorg Massen et al
To gain or maintain social standing, ravens intervene in the affiliative interactions of others, even though such interference is potentially risky and without immediate benefit.
Because of their already established power, allied ravens can afford such risky strategies. They specifically target those ravens that are about to establish a new alliance and might thereby prevent them from becoming future competitors through a divide-and-rule strategy. ~ Jorg Massen
Corvids use deictic gestures in the same way as primates: using their beaks like hands to point and draw attention to a certain object or location. Such behaviors develop bonding relationships and reveal affinities to others.
Corvids infer the intentions of others. A raven will move cached food if another raven appears to have seen the stashing but will leave a stored bit in place if ravens are around that couldn’t know.
A pet dog will follow the gaze of his master to hidden food. A corvid has no master, but readily watches such gazes to concealed meals.
Eurasian jays plan their meals. Males anticipate and cater to their mates’ desires when foraging. If a male wants something other than his mate, he takes her wishes into account. Most often he feeds her what she wants. This clearly demonstrates an empathic theory of mind.
Corvids are apt logicians. When faced with tests to obtain food requiring a varied, elaborate procedure, corvids imaginatively consider the situation; then, without any experimentation, succeed in retrieval. In contrast, people faced with such a challenge take a piecemeal approach and rely upon trial and error. Corvids surpass humans in problem-solving.
Corvid problem-solving acumen comes from their innate understanding of physics coupled with excellent memory. Corvid comprehension of physics is more nuanced than chimpanzees possess, and appears even superior to that of humans, who begin to acquire their physics sense at 6 months of age.
A crow knows how much something weighs by seeing how it reacts to a wind. Crows can solve practically any problem involving natural phenomena. They falter with contrived problems that are counter-intuitive, as do humans.
Causal reasoning is the mental ability to infer an unperceived mechanism for an effect that is detectable. Human infants as young as 7 months possess causal reasoning; so do crows, though how early in life they get wise to the unseen is unknown. Crows ability to understand causal properties more than rivals that of 5- to 7-year-old children, which is about as far as most people get.
The ability to make inferences about hidden causal mechanisms underpins scientific and religious thought. It also facilitates the understanding of social interactions, and the production of sophisticated tool-using behaviors. ~ English corvid researcher Alex Taylor
Tool Use
Creatively fashioning tools is common among corvids. Crows create tools that require manipulating a substrate material, such as breaking a twig, stripping off its leaves, and honing its tip to a fine hook.
Corvids make tools using a combination of materials. They manufacture tools of greater sophistication than those that chimpanzees have been seen to make.
The tool of choice depends upon the task at foot. Different groups use different tools based upon local custom.
New Caledonian crows, which live in family groups, have cultural traditions relating to tools. But then, these corvids have a strong innate fondness for tools. Young crows at 2 1/2 months spontaneously begin to use available tools, even without training. Like a mathematician fiddling with a pencil while worrying over a problem, these crows compulsively grab a stick and twiddle it when struggling to figure something out.
New Caledonian crows combine objects to construct compound tools. These crows solve novel problems rapidly. ~ German zoologist Auguste von Bayern et al
Corvids use their tools in different ways depending upon the situation. Rapid poking is used to prod prey under leaves, whereas slow patient movements are employed to hook a food source from a difficult-to-reach spot.
Crows carry their favored tools with them, tucking them under their feet when feeding so as not to lose them. Crows foraging up high, where a fallen tool would be troublesome to retrieve, are more apt to store them in tree holes for safekeeping.
Parenting
As with other corvids, New Caledonian crows have nuclear families. A mated pair stay together year-round, constantly reaffirming their bond by mutual grooming and feeding, and intimately relaxing by sitting next to one another. They don’t even mind if one partner plays with the other’s favorite tools.
Offspring live in a stable and loving home. They are led by example and offered positive reinforcement. Parents are patient and persistent in teaching their young, as well as taking prodigious care of them into near adulthood. The family forage together, often talking in quiet voices.
Young crows stay with their parents for 2 years or more. This is a quite extended dependency by avian standards. It pays off in producing the brightest birds.
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Jackdaws
Jackdaws, gregarious and voluble, establish a pecking order in their flock. In stark contrast to chicken hens, who may peck at any inferior, jackdaws worry only about keeping the next-in-line in line.
Jackdaws prefer to be as peaceful as possible. They respect established social boundaries.
Not only physical strength, but also personal courage, energy, and even the self-assurance of every individual jackdaw are decisive. This order of rank is extremely conservative. An animal proved inferior, if only morally, in a dispute, will not venture lightly to cross the path of its conqueror. ~ Austrian zoologist Konrad Lorenz
Jackdaws mate for life. Young males establish their rank before choosing a wife.
Unmated females are the lowest on the pecking order. A female assumes the status of her mate; a social convention universally respected.
Jackdaws are unique among corvids in that they nest in natural cavities in trees, of which there are a limited supply. A jackdaw warns off interlopers by intimidating looks, using another jackdaw singularity: bright eyes. Unlike their dark-eyed relatives, jackdaws have pale irises. Set against their dark face feathers, this makes the object of their gaze obvious.
Pinyon Jays
Pinyon jays are an especially gregarious North American corvid. They live in permanent flocks of up to 500 individuals, breed colonially, and have long-term, multigenerational relationships within a social dominance hierarchy.
A pinyon jay knows its place in the pecking order. It also can figure out the rank of a bird not known to it by how the stranger interacts with another jay that is familiar. Pinyon jays can indirectly infer a stranger’s social rank.
Transitive inference can be seen in several corvid species, and, as aforementioned, in chickens. Rats and monkeys are also known to be able to figure out relationships between objects or others via indirect evidence.
Magpies
The Thieving Magpie is a melodramatic opera by Italian composer Gioachino Rossini. It is a tale of a maid who almost goes to the gallows for stealing silver, before it is discovered that the culprit was a thieving magpie, which had been taking and stashing items in the church tower.
European folklore tells of magpies as fond of shiny objects, and prone to collect them. However well sung the story, it is a myth. Magpies are initially more spooked than attracted to shiny objects, which are not normally found in Nature.
Magpies are considered one of the most intelligent animals. The European magpie readily recognizes itself in a mirror.
Several black-billed magpies were observed retrieving grass and placing it on the body of a dead friend. They stood vigil, grieving for some time before flying off, leaving the corpse and tribute behind.
Magpies are not the only corvid with admirable emotional stature. Other corvids, including Western scrub jays, have been seen grieving over lost friends.
