Bob D. writes:
I really enjoy your column/page. I have a question about birds. How do individual birds (of the same species and gender) identify other specific individual birds? I’ve tried to notice differences, but I just can’t see them. What am I missing?
That is a good question, and the answer is not as simple or as straightforward as you might expect. Humans recognize each other using many senses. Visual discrimination is often the strongest. Researchers believe our brains contain a specialized region that responds more strongly to faces than to any other object. This area is said to activate even in people who are born blind and simply touch a face! As we all know, humans can often also recognize other individuals from their voices. So people use both visual and auditory cues to identify others.
How do birds identify each other? Most birds see farther than humans. An eagle can spot a rabbit from a mile away. Most birds perceive ultraviolet light, which can reveal feather patterns. We can see the shimmering iridescent purples and greens in a starling’s plumage. But can you imagine how multifarious it is through ultraviolet light? Females scrutinize male plumage when selecting mates.
Generally speaking, birds see more colors more vibrantly than us, with four types of color receptors in their eyes (compared to three ours). Owls can see at night. Seabirds have oil droplets that cut glare and improve distance vision.
Given that birds are so richly endowed, it would not be surprising to learn that they use visual cues to identify other birds. But do they? Bird vision is understudied, but scientists do know that chickens have a pecking order based on recognition of visual cues, such as plumage, color, deportment, and comb shape.
In one study, scientists found that rooks (a type of crow) look more often at a video of their mate than at videos of other birds. It’s clear that rooks recognize their partner visually, but it is less clear what visual cues they discern: Is it the face, the beak shape, the gait, body contours, plumage color? We do not know.
Carrion crows recognize the faces of their mates even when the faces are upside down. Humans and other primates are not good at recognizing upside-down faces. Some crows even remember human faces if the humans were cruel to crows.
It is thought that certain facial features are more important to birds than other features. For example, when researchers showed male pigeons images of female pigeons, the males cooed less when the female’s beak was removed or enlarged than when her eyes were changed. (Cooing is a courtship behavior.) This may suggest that beak shape is more important to pigeons than eye features.
Like humans, birds use auditory cues to recognize others. Birds have acute hearing that is sensitive to subtle sound differences. Birds use these sound differences to identify other birds. While a human voice box produces only one sound at a time, a bird’s voice box, called a syrinx, can produce two notes at the same time. The left side produces lower-pitched notes; the right side, higher notes. Studies have shown that many songbird females listen closely to the song quality of males to determine the best mates.
An emperor penguin, too, relies on its syrinx. This penguin does not build a nest but instead incubates and carries its egg on its feet. A mated penguin cannot head back to the nest to find its partner. Instead, the bird couple finds each other by their complex calls, which travel long distances and through the bodies of other penguins in the colony.
American goldfinch females respond to distinctive flight calls of their mate, but not to the calls of other males. And some crows respond to the calls of a sibling, even after 10 months of separation. Zebra finches can recognize multiple types of calls of different individuals.
In another study, researchers took baby swallows out of their nest. Then they played the recorded sounds of the babies on one side of the nest and the recorded sounds of different babies on the other side of the nest. Of course, the parents went straight to the sound of their own babies. (This result surprises no mother.)
Birds use olfactory cues to recognize others as well. Historically, scientists thought birds had a poor sense of smell. Because of this, they did not test how well birds used olfactory signals. But recent studies show that birds collect preen oil from a gland near their tail and rub it onto their feathers. The unique scent profiles from this volatile oil communicate information about a bird’s health, hormonal status, and identity. Some birds, such as dark-eyed juncos, use these odors to identify mates.
To sum up, birds use superb vision, acute hearing, and a remarkable sense of smell to identify mates, family members, and enemies. How come you can’t identify individual birds? Perhaps you don’t notice subtle differences to which birds are attuned. Or perhaps it’s because some important bird cues — ultraviolet markings, subtle two-toned calls, and distinctive preen oil scents — are undetectable to humans.
Have you taken photos of our urban wild things? Send your images to Cambridge Day, and we may use them as part of a future feature. Include the photographer’s name and the general location where the photo was taken.
A stronger
Please consider making a financial contribution to maintain, expand and improve Cambridge Day.
We are now a 501(c)(3) nonprofit and all donations are tax deductible.
Please consider a recurring contribution.