The Bird Way: A New Look at How Birds Talk, Work, Play, Parent, and Think

by Jennifer Ackerman

There’s even a term for it, Davian behavior, coined by Robert Dickerman—known as the biologist who gave necrophilia a good name. Dickerman speculated that the “lordosis” posture of a dead ground squirrel, with back arched downward, might release the copulatory drive in a sexually aroused male. And indeed, when biologist David Ainley conducted an experiment on Adélies with a dead female penguin frozen into position, he noted that older males found the female corpse irresistible.

It’s not so simple. Kaeli Swift and John Marzluff found that during the breeding season, crows also tried to mate with a lifelike crow in a neutral standing position and with a crow lying on the ground in a “dead” position, its wings tucked close to its body—the latter effort accompanied by plenty of scolding. Maybe it’s not the copulation position per se that inspires arousal, say the scientists. A dead posture excites alarm, which is not uncommonly followed by sexual behavior. This sex-after-alarm response has also been noted in zebra finches, vermilion flycatchers, and pied avocets. Swift and Marzluff point the finger at hormones.

In the past decade or two, several pairs of same-sex penguins in captivity have attracted international attention by engaging in sexual behaviors and raising chicks together.

The male starts his performance by making a tool. With his huge hooked bill, he shears off a sizable stick from a tree, snips off the foliage, and then trims it to pencil size. This in itself is a wonder. Toolmaking of any kind is rare in the natural world and almost always occurs in the context of foraging. “This is the only species other than humans we know of that makes a tool for display or for musical purposes,” says Heinsohn. Holding his neatly fashioned drumstick in his left foot, the cockatoo beats it against his perch or the hollow trunk of a tree. When things really get going, he might mix in a high-pitched hooting whistle or lift his crest feathers, bob, sway, pirouette, and flash those naked cheek patches, bright red with flooded blood.

https://youtu.be/2MIoXh_ORMw

This discovery of a musical beat in the wild supports Darwin’s assertion that rhythm has aesthetic appeal across species and may reflect some ancient shared aspect of brain function. As he wrote in The Descent of Man: “The perception, if not the enjoyment, of musical cadences and of rhythm is probably common to all animals and no doubt depends on the common physiological nature of their nervous systems.”

here you get a situation where males work together in cooperative partnerships that may last as long as six years.” But here’s the thing: Only the dominant male of each pair gets to mate with the females the partners attract. Why would a male bird forgo his own mating opportunities to help another male secure his? What’s in it for the wingman?

“The display is more of a three-bird ballet than a simple spectator event,”

In Descent of Man, he argues that many elaborate displays in male animals result from the kind of evolution he called sexual selection. Females fancy males with certain traits over other males. The chosen males have more offspring, which inherit these traits, so they’re passed along to the next generation and hence spread through a population. The outlandish displays we see today are echoes of female choices in eons past.

Sexual selection may run counter to natural selection, driving the evolution of extravagant male courtship traits that actually hinder survival tasks such as finding food and avoiding predators. In this way, males may end up with elaborate traits and displays that are burdensome but so sexy they’re perpetuated in the population.

Scientists have known for some time that these hummingbirds execute wild dives during their displays, that they flash their brilliant gorgets, that they make special sounds. Christopher Clark, now a biologist at the University of California, Riverside, discovered that these sounds are not vocalizations but sonations, mechanical noises the birds make as air passes over specially modified feathers in their wings or their tails and vibrates them.

From elaborate displays, then, females may glean information about male fitness and quality, his “good genes.” That’s one idea, says Stoddard, but there are others. The “signal efficiency” theory, for instance, which might be called the bright beacon hypothesis: Complex signals may have evolved not because they’re conveying information about quality, but because they efficiently communicate, “Here’s a male who is ready to mate!” The more signals you make, and the brighter, louder, and flashier they are, the more conspicuous you will be to members of the opposite sex.

In addition, the more complex the signal, the more likely it is to hold the attention of a female. If a simple signal is repeated over and over, she may become habituated to it, and her interest may wane. In general, birds pay less attention to constant noise than to the sporadic or unexpected sound of a hawk call or a branch cracking beneath the paw of a predator.

To attract females, males build bowers, ornate structures made of sticks and decorated with ornamental objects. These are not nests; no raising of young takes place here. Rather they are theaters for seduction, the stage a male bowerbird uses as a backdrop for his song and dance to woo visiting females. Of the nineteen species of bowerbirds, fifteen build bowers, each favoring a different structure and different sorts of decorations, each remarkable in its own way. Macgregor’s bowerbirds build a maypole spire of twigs and sticks up to three feet high and circled with moss and piles of insects, nuts, and fruit. Male satin bowerbirds collect blue objects and paint the interior of their bowers, chewing up dried hoop pine needles and applying the resulting brown paste to the inside of their bower walls. Only humans and a few other animals create more lavishly decorated structures.

When a male great bowerbird displays, he stands at the edge of an avenue entrance so just his head shows to the female in the avenue, then plucks up a decoration and parades it in front of her before flinging it across the court in favor of a new decorative object. The color pops against the monotone gray-white background of the bones and stones. On average, he flashes five objects per display, alternating these with a quick flare of his magenta crest. And here’s the astounding thing—males boost the impact of the colors in their show with a special technique: They build the interior of their avenues with red sticks that create a reddish light within the bower, actually changing the way the female sees. Exposure to this reddish light for a minute or more results in chromatic adaptation in the female’s eyes, altering her perception of the colored object he displays.

And once the choice is made? Is it made only once? Are birds loyal to their mates? Not by a long shot. It is now well known that sexual monogamy in the bird world—once considered the predominant way of mating—is largely a myth.

Driving through the countryside in Kalimantan, Borneo, you can see huge three-story concrete structures with tiny windows—far larger than any house in the region. These are homes for the edible-nest swiftlet, a bird that makes its nest out of its own saliva hardened into a woven cup. The little white nests, about two inches across, are considered a delicacy in bird’s nest soup, one of the world’s most expensive foods, so they’re “harvested” in buildings designed to resemble the enormous rock caves where the birds normally nest.

“There’s more and more evidence that birds build their nests flexibly, in response to weather conditions and the materials they have available in their environment,” she says, “and that they use their own past experience in making decisions.” That is, nest-building behavior is far from hardwired or fixed. At least in some cases, it may be learned.

Birds building nests at temperatures of 64 degrees Fahrenheit add more material to their nests, making them 20 percent heavier than the nests of birds building at 86 degrees Fahrenheit. This may be hopeful news, suggesting that some birds show flexible nest-building behavior in response to ambient temperature, which may help them adapt to climate change.

pedestrian magpies attack only certain people. “That’s the other big thing we discovered,” says Jones. “These birds recognize individuals. They live in a little territory and they never leave it, so they know every human that lives around the place. They see kids growing up, and they remember them. These birds are very, very smart. They’re watching us and interpreting our behavior.” The magpies live on average for twenty years and can remember up to thirty human faces for about that long, says Jones, “so if you anger a magpie once, you’re going to get attacked again and again.”

Birds also foster the young of other species.

the two poles of bird parenthood—group parenting and no parenting. In nearly 10 percent of species, from white-winged choughs to acorn woodpeckers, multiple adults band together to dote on their young until they’re fully independent, sometimes for many months, even years. On the other hand, a small number of species, around 1 percent of birds, save themselves the trouble of parenting altogether,

When he first came to Brisbane in the 1990s to do his PhD on brush turkeys, he had to travel to the rainforests of Papua New Guinea to find them. Now, they’ve moved into populated areas everywhere across southeast Queensland and are thriving as urban birds, building their enormous mounds in parks, gardens, backyards, even driveways.

“These birds are the most spectacular engineers of any animal because individuals can produce such a monumental change in an ecosystem,” says Jones. “In the rainforest, the organic matter on the humus layer is the engine that drives the nutrition for the forest,” he explains. “Brush turkeys scrape up all of the organic matter from a big circle with a one-hundred-meter radius, all the seeds, all the fruit, everything goes into the mound and is compacted in that one place, so they’re actually manipulating the structure of the forest.” Wherever it’s located, in rainforest or suburban backyard, the mound acts just like an enormous compost heap.

It takes her only a few minutes to lay her eggs before the male chases her off the mound and fills the hole. Away she goes, never to interact with her eggs or young again. You can hardly blame her for not hanging around given the graces of her mate. Meanwhile, the male continues tending and protecting his mound. He’ll fight off anything that threatens his eggs,

When the baby bird finally breaks into the light of day, it pops out as the most advanced chick of any bird species, instantly able to fend for itself, to run, feed, and fly. “Brush turkey chicks are so super precocial they almost require their own terminology,” says Jones. They need to be. You would think after all this that the chicks’ father might be waiting with a mouthful of food. But no. He’s actually a threat. “If a chick is unlucky enough to meet Dad on the way out,” says Jones, “he has no idea what the chick is. It’s just some horrible thing in his mound. And—I’ve seen this many times—he just boots it off into the bush.” The chicks survive this paternal hurling. What they don’t survive—and this is the absolute cost of having no parental care, says Jones—are the cats and dogs and foxes and goannas and everything else around the place intent on eating them. “There’s no parent to tell them what a predator looks like, what’s an appropriate behavior if a cat comes up, how to hide, what to do.” Some 97 percent of brush turkey chicks don’t make it through the first week.

It flits from perch to perch, emitting its persistent call. The hunter follows. This pattern of leading and following is repeated until the bird reaches the treasure: a nest of bees ensconced high in a broad-leaved tree or tucked into a rock crevice or termite mound. Once close to the nest, the honeyguide perches nearby and lets out an “indication call,” softer in tone, with longer pauses between notes. Not just any human call will elicit this behavior. Among the Yao, it’s that trill-grunt call, brrrrr-hm! For Hadza-speaking people in Tanzania, it’s a melodious whistle. In recent experiments, evolutionary biologist Claire Spottiswoode and her colleagues played the trill-grunt call of the Yao honey-hunter, an unrelated Yao call, or the song of a ring-necked dove and then tracked the birds’ responses. In two-thirds of the trials with the trill-grunt calls, the birds responded by guiding the honey-hunters, leading them straight to a bee nest in more than 80 percent of the forays.

In this way, birds and humans communicate. “The honey-hunters use these special calls to signal honeyguides they’re eager to follow, and honeyguides use this information to choose partners who are likely to be good collaborators,” says Spottiswoode. It can work the other way, as well, with a bird initially summoning human partners with its special loud chattering come-hither call. The bird literally points the way to hidden bee nests; from its calls and its flight and perching pattern, the honey-hunters construe the direction and distance to the nest. After the hunters harvest the honey (subduing the bees with smoke), they leave the energy-rich honeycomb wax for the birds to feast on.

Brood parasitism is extremely rare in the vertebrate world. It occurs in a few kinds of fish and in some species of ants, bees, wasps, beetles, and butterflies, but no reptiles or mammals. In the bird world, just 1 percent of species, around one hundred, are so-called obligate parasites, dependent on this way of reproducing. The strategy is risky, but for some birds, it seems to work. It has evolved independently at least seven times in different bird lineages: in ducks, honeyguides, finches, and cowbirds, and three times in different lines of cuckoos.

The female honeyguide incubates her egg inside her body for an extra day before dumping it in the bee-eater nest. This means that her chick will hatch ahead of the host eggs, the better to ready itself for what comes next: murdering its nest mates. The weapon is a pair of needle-sharp hooks at the tips of the chick’s beak, which it uses to stab its foster siblings one by one as they hatch.

A common cuckoo chick adapts the “push from a height” strategy seen in Hitchcock’s Rear Window, hoisting a host egg or even a newly hatched chick onto a small indentation in the middle of its back and then, with its legs braced against the sides, tipping it up and out of the nest—all with its eyes closed.

How does a baby brown-headed cowbird know it’s a cowbird and not a kinglet or a meadowlark? When nestlings are “cross-fostered,” put in the nests of other species, most species imprint on the foster parent and learn its behaviors, songs, even mate choice decisions. “Yet somehow brood parasites avoid this mis-imprinting,”

brown-headed cowbird mothers use a special “chatter call” that gives nestlings a key bit of information: self-knowledge. “The female brown-headed cowbirds produce the chatter call in different social contexts,” says Louder. “The call acts as an acoustic password cue for her offspring, guiding their choices about who they learn from, so they learn the songs of their species and identify appropriate mates.” Hearing the password actually changes the brains of the young birds, transforming the auditory region of the brain into a state ready for learning the songs of their own kind. In this way, a mother cowbird tells young cowbirds who they are and what they should become—a brood parasite rather than a member of their host species.

Eggs have traditionally been seen as the main battleground of brood parasite and host in their evolutionary arms race. The story goes something like this: A brood parasite targets a new host species, duping its victim into accepting its egg and raising its offspring. Eventually, the host evolves the ability to detect the foreign eggs and reject them. The parasite then evolves eggs that mimic the color and pattern of the host’s eggs so closely that they escape detection. In turn, the host has two defenses: change the look of its own eggs, or heighten its ability to distinguish them from those of the interloper. And so it goes. It’s a high-stakes game of evolutionary ping-pong. For every defense evolved by their hosts, cuckoos retaliate by evolving ever trickier means of fooling them. Each move is met by a countermove.

“To answer this question, I knew we were going to need what amounts to facial recognition software for eggs,” says Stoddard. The differences in pattern and color in these host egg types are so subtle that they often can’t be detected by human observation. “You can’t pick up the difference by eye—you really need a computer to analyze them,” she says. So Stoddard teamed up with a computer scientist, Chris Town of the University of Cambridge, and created NaturePatternMatch, software that identifies features on an egg that are likely important to a bird.

The program yielded just what Stoddard and her colleagues had hoped: clear evidence that several host species have added to their eggshells individualized signatures, “just as a bank adds special watermarks to its dollar bills,”

set. The hosts of common cuckoos almost never reject cuckoo chicks—even though they look nothing like host young. Even a few weeks after hatching, when a cuckoo chick is more developed, the host birds are strangely incapable of identifying the little monsters that have hijacked their nest, and will care for “Rosemary’s baby” until it fledges. There’s a theoretical model suggesting why this is so. Bird parents “imprint” on the chicks that hatch from the eggs in their very first clutch, and after that, reject any chick that’s different. Host parents that are unlucky enough to be parasitized in their first clutch will imprint on the cuckoo chick and rebuff their own young forever after. The high cost of mistakenly imprinting on a cuckoo nestling should prevent host birds from evolving the ability to reject chicks.

“Here, the arms race between cuckoo and host has escalated to where hosts can discriminate cuckoo nestlings,” says Langmore. And here’s the extra-cool thing, she told me. In Australia, not only do the hosts break the rules, so do the cuckoo chicks. “Because of this good recognition ability in hosts, cuckoo chicks have evolved wonderful mimicry of host young, either in appearance or in begging calls, which you don’t get anywhere else.” The bronze-cuckoos, which target fairy-wrens, thornbills, and gerygones, she says, “have evolved these fantastically matching chicks that mimic the size, the skin color, the down color, even the mouth color of the host species.”

collecting cuckoo alarm calls from all over the world, including Africa, India, China, Indonesia, and Japan to see if birds from different countries respond to one another’s cuckoo alarm calls. “It would make sense from an evolutionary standpoint that host species in different parts of the world have converged on a common cuckoo alarm call,” says Feeney. “Cuckoos are a unique kind of superweird threat—they’re no danger to the adults, just to the young.

In Feeney’s view, brood parasites may be driving convergence in an alarm call that effectively screams cuckoo in any bird language. “We know that information transfer about the risk posed by parasites is important within a species,” says Feeney, “but if parasites pose a threat to multiple species, it might make sense for information about the threat to also transfer across species—perhaps to facilitate a kind of behavioral herd immunity.”

He mentions a study published by a team of scientists in 2016 that analyzed the associations in sound and meaning in thousands of human languages. The team found a hundred or so archetypal words that are similar across continents and linguistic lineages—among them star, leaf, knee, bone, tongue, and nose. The distribution and history of these associations suggests that these archetypal words weren’t inherited or borrowed but emerged independently. Could the same thing be happening in birds? asks Feeney. “Could there be an international bird word for cuckoo?”

For each nest, the cuckoo watches the female fairy-wren build and then, once she’s finished, sneaks in when the parents are out and checks the nest to find out whether the fairy-wren has laid yet. Fairy-wrens lay in a short three-day window, so the female cuckoo must time her egg deposits just right.

The cuckoo checks the nests regularly to see how many eggs there are. When it comes time to lay, she will remove one egg and replace it with her own so that the wrens will be fooled into thinking their clutch is intact.

Finding the nests, watching them, carefully timing the laying of her eggs to overlap with egg laying in her hosts: all this while avoiding detection, which might set the whole neighborhood abuzz and rally mobbing. She has to do this ten or twelve times in a season, which means she has twelve pairs and twelve nests to keep track of. She tunes in to the activities of all of them, observing keenly, moving around and making mental notes.

Now we know that 9 percent of bird species breed cooperatively and share parental care,

Why would an individual give up its own breeding opportunity to act as a helper, assisting others to raise their young? Darwin worried that equivalent behavior in bees and other insects was possibly fatal to his theory of natural selection. The same William Hamilton who despaired over the coloring of the eclectus parrot is credited with rescuing Darwin’s theory in the 1960s with his theory of inclusive fitness, also known as kin selection—which suggests that helping your close relatives can be a good way to pass on your own genetic material because relatives share a percentage of your genes.

Together each group builds a shared nest in which all of the females collectively lay their eggs more or less synchronously. They all share parenting care, raising the mixed clutch of young until they fledge.

Parents took turns feeding young, visiting the nest at similar rates. But if you removed one member of the pair, the other would deliberately compensate, working harder to fill the gap. This suggests that each parent monitors the other’s investment and decides how much care to provide.

Once the first egg appears, however, things may take a decidedly less cooperative turn. A female who hasn’t started laying herself will unceremoniously remove any eggs she sees in the nest.

Why would breeding females in these tight-knit and egalitarian cooperatives eject eggs laid by their fellow group members?

The female ani that lays an ejected egg doesn’t resist the displacement. “She neither attempts to guard her eggs nor retaliates against the female that evicted it,”