Feb 14, 2020 | Featured in: Watching Backyard Birds, February 2020

Love / Birds

Those of us who enjoy watching our backyard birds sometimes see a male and female cardinal canoodling on a branch, or even exchanging a bit of food—which looks like a kiss.

February is the month for love. According to Cole Porter, "Birds do it, bees do it, even educated fleas" fall in love. It's sweet to imagine that they do.

But do birds really "love" their mates? The answer is impossible to know, and certainly requires anthropomorphizing. We know that birds and humans share some emotions, with fear being perhaps the most obvious. But what about love? Many birds (male hummingbirds are an exception) are devoted parents, who seem to care for their nestlings and fledglings lovingly. But is that really love? What about birds who mate for life? Could their pair bond be called love? Ornithologists can't tell. Mating behavior can be observed, but among birds (or humans), mating is not the same as love.

Those of us who enjoy watching our backyard birds sometimes see a male and female cardinal canoodling on a branch, or even exchanging a bit of food—which looks like a kiss. I rarely see a single Carolina wren on my deck—it's almost always a pair. Are those birds in love? Just dating? Or maybe just friends? It's impossible to tell.

Although we like to think of paired birds as "married," among backyard birds, mating for life is the exception, not the rule. Many backyard birds form pair bonds that typically last for one or a few breeding seasons. Together, they tend their nestlings and fledglings. But the little ones they so lovingly care for might not all have the same father. Paternity tests of nesting birds show that dalliances are fairly common among songbirds.

Monogamy Among Birds

Rock pigeons are among the species that mate for life, finding a new partner only when a mate dies or disappears for an extended time.

Carolina wrens and rock pigeons, however, are exceptional. They do mate for life and seldom "cheat" or "divorce." Bewick's wrens and mourning doves are similarly faithful to their partners, but they seldom mate for life. In those species, pair bonds last one breeding season, or sometimes longer.

Monogamy does not have the same meaning for birds as for humans. Among humans, the term "monogamous" refers to a couple who, "forsaking all others," are faithful to each other. A time span of that commitment is not always stated or implied, so humans, like mourning doves and Bewick's wrens, can be serially monogamous—faithful to one partner at a time. About 90 percent of bird species are monogamous, but two types of monogamy are recognized: social and genetic.

When DNA tests of all the young in a nest determine that both parents attending it are the biological parents—and this is generally true for all the birds of that species—the species is considered to be genetically monogamous. No evidence of dalliances or cuckoldry is found. Examples of genetically monogamous species include rock pigeons, mourning doves, Carolina and Bewick's wrens, most swans and geese, loons, many birds of prey, some gulls, and jays. Some of these species mate for life, finding a new partner only when a mate dies or disappears for an extended time. Others are genetically monogamous only for as long as the pair bond lasts.

The majority of songbird species, however, are socially monogamous: A male and female form a pair bond and produce and care for the offspring in their nest. However, dalliances occur, and many nests contain young from a different father (or fathers). That is, most songbirds—males and females—despite their pair bond, cheat on their partners. Even so, their pair bond—family loyalty if not sexual fidelity—can last for several breeding seasons. "Divorce," however, is quite common.

Backyard Examples

American goldfinches are socially monogamous—they are loyal to their family, but often unfaithful to their partners.

American robins are socially monogamous, with pair bonds generally lasting for one entire breeding season. Genetic testing shows that about half of all robins are the offspring of "extra-pair copulation," which means they were not sired by the daddies who cared for them when they were young. Even though robins "cheat" and may know that some of the young in their nest are not their own, they don't show favoritism when caring for their nestlings.

Northern cardinals form pair bonds that last from early spring through winter, but divorce is common between seasons. Between 9 and 13 percent of all cardinal nestlings are the product of extra-pair copulation.

Song sparrows, too, form pair bonds that last for the breeding season, but more than 15 percent of all young were not sired by their "social" father.

Black-capped chickadees form pair bonds that can last for several breeding seasons. Over the course of 10 years, 15 percent of the chickadee population divorced. Extra pair copulation was detected in about 30 percent of all nests, and from 9 to 15 percent of all young chickadees were the product of extra-pair copulation. Carolina chickadees, however, appear to be faithful to their partners while bonded.

American crows often mate for life, but they cheat. An average of 8 percent of crow nestlings came from a different father.

Most woodpecker species seem to be genetically monogamous, with pair bonds lasting till death do them part. Extra-pair copulations are rare, although research is scant. Acorn woodpeckers, however, can be polygamous and communal, and even homosexual behavior has been observed!

American goldfinches are socially monogamous—they are loyal to their family, but often unfaithful to their partners. Pair bonds often break during the breeding season and do not continue into the fall and winter. DNA testing shows that 20 to 25 percent of American goldfinch nests have broods sired by more than one male.

Eastern bluebird couple at a nest box.

About 20 percent of eastern bluebirds were not sired by their attending father, and male bluebirds sometimes take an active role in tending two females and their nests in nearby nesting boxes.

Similarly, male house wrens sometimes care for two females and their young in nearby nest sites. Mate switching between broods is common.

Hummingbird males have no role in nest building, incubating, brooding, or tending the young. Their only role is territory selection and defense, impressing the female, and copulation. By human standards, hummingbirds are terrible fathers.

What's Love Got to Do with It?

Northern cardinal couple at a backyard feeder.

Back to love. So, when you see what appears to be a happily mated pair of birds at your feeder, or happen upon a songbird nest full of eggs—even of a socially monogamous species—there may be a more complicated situation than is apparent.

The language we use to describe these relationships is laden with human values: "cheating," "fidelity," even "divorce," and that's too bad. We shouldn't judge. They're birds, after all. They are behaving as their ancestors have for countless generations—in ways that have enabled survival of the species.

Do birds fall in love? Cole Porter was not an ornithologist. The idea that birds love is charming, but without the assistance of Doctor Doolittle, we'll never know for sure.

About Jackie Berkebile

Jackie Berkebile is a regular contributor to Watching Backyard Birds. To date, she has penned five articles for the magazine.

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    by Liza Fox, Sun, 15 Nov 2020
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