When my children were growing up, we had a bird feeder right outside the kitchen. One morning, I found my younger daughter kneeling on the floor, her face close to the window, murmuring, “Are you a mommy bird or are you a daddy bird? And what about you, little bird? Are you a mommy or a daddy?”
Like every other vertebrate, birds come in mommies and daddies. Sometimes, those mommies and daddies look almost identical, sometimes there are subtle differences, and sometimes the differences are dramatic.
Many species of birds exhibit sexual dimorphism. That is, males and females differ in size and/or colors. Cardinals are a great example. The “daddies” are brilliant red while the “mommies” are light brown with some red only in the wings, tail and top of the head. Most kinds of ducks also show significant differences between male and female. And it’s only the male red-winged blackbirds that are black and have red wings; the females are mostly brown.
Sexual dimorphism is a handy evolutionary device. A female’s quieter colors provide camouflage when she’s sitting on the nest, while a male’s bright plumage catches the attention of predators, so papa can lead danger away from vulnerable young. And, of course, the brilliant plumage also catches the attention of females!
Other birds have evolved more subtle gender differences. Female robins are only slightly paler than males. Female white-breasted nuthatches have slate gray on the tops of their heads instead of black.
But in a large percentage of birds, males and females look identical to us. All adult blue jays look similar. Every single chickadee looks black, white, soft, and cute. For many years, it was believed that the sexes look alike in about three-fourths of the world’s songbirds. However, scientists have discovered that this apparent sameness isn’t real. It’s what we humans see, but not what the birds see! Humans can see colors only from red to violet, but many (maybe most) songbirds also see at the ultraviolet end of the spectrum.
When chickadees look at another chickadee, using far more sensitive eyes than we have, they immediately see that males show a much greater contrast between black and white and much larger “bibs” than females. These differences are evident to humans only if the birds are seen under ultraviolet light. Being able to see a wider spectrum of colors means that small birds inhabit a very different world than we do. Hummingbirds, for example, see a bee balm flower as a twinkling carnival display of glowing purples and pinks and jewel-tone sparkles.
In another fascinating bit of evolutionary “logic,” raptors such as hawks see light only in the same parts of the spectrum that humans do. So, when a male songbird is strutting his stuff to attract a female, the gloriously glowing parts of his plumage don’t also grab the attention of a hungry raptor.
As you enjoy the birds coming to your feeders this winter, enjoy the dramatic differences in sexually dimorphic species. Look for more subtle differences in other species. And try to imagine how much more gorgeous some of the males would look if you were another bird!
Maeve Kim, a local bird expert and author, loves birds. She watches birds, feeds birds, travels to see birds, teaches about birds, and writes about birds. In her latest novel, “Ivy’s Optics,” every character is either a bird or a birder. For more birding photos and adventures, visit vtbirdsandwords.blogspot.com.