Suzanne Charlé  |  March 11, 2021

Lifelong bonding, casual encounters, creative ways to attract a mate, parental strife, and sibling rivalry: as Dr. Wenfei Tong notes in discussing her book Bird Love: The Family Life of Birds, the diversity of behavior in the avian world “is not so different from human behavior and the challenges we face.”

 

In this informative, handsomely illustrated book, Dr. Tong details the diverse ways birds have evolved to pass their genes onto the next generation, ranging from courtship rituals and nesting designs to protecting eggs and raising chicks. A research associate at Harvard who teaches evolutionary biology at universities in Montana and Alaska, Dr. Tong notes: “Bird family life can look rosy.” But she cautions there is “a darker side, including sexual conflict, infanticide, and siblicide.” Bird Love explores, with insight and humor, how and why both sides of bird family life have evolved. 

 

Consider courtship and mating: Albatrosses mate for life. Living over 40 years and with few predators, they can apparently afford to take their time, and they do: it may take four years for a pair to bond before the female lays one egg. Other species attract mates through show. In East Africa, the male Long-tailed Widowbird can be seen from half a mile away. Like a flashy Porsche, the bird’s long, 20-inch tail is expensive to maintain, and attracts female attention—a signal that the male is in good health and a good genetic choice to produce offspring. (The same is true for birds with intense red coloring, the product of carotenoids; only an individual with a strong immune system “can afford to squander carotenoids on looking good.”) In some cases, females choose brains over beauty and brawn: The male Satin Bowerbird constructs a bower, elaborately decorating its entrance with blue objects to lure the female.

Bird nests are constructed in a variety of ways, with various advantages. Weaverbirds weave intricate nests, which often include fake entrances to confuse predators and parasites, while the alert male American Robin will build a second nest soon after his first brood has hatched, to makes sure that his mate will stick with him. (If he doesn’t, she may abandon him for another male that has a nest ready.) House Sparrows litter their nests with cigarette butts, which biologists have discovered deter lice.

 

Sex roles can be flexible, and sometimes reversed. In the case of the gallinule-like jacana, the female is the larger, showier, more aggressive sex: the brightly colored bird will compete with other females to gather a harem of males, who perform all the parental duties (including even rescuing chicks from crocodiles).

Birds’ genetic response to childcare is a crazy patchwork of reproductive investment strategies: most songbirds, whose chicks depend on their parents for all their needs after hatching, share in the tasks of feeding, while Kentish Plover chicks are so independent (able to walk three quarters of a mile within hours of hatching), that the female takes off to find another mate elsewhere, leaving the male to supervise. Common Loon chicks can dive within a few days of hatching, but continue to ride on their parents’ backs and be fed by them. 

 

Some species, like the Brown-headed Cowbird of North America and Common Cuckoo of Eurasia, shrug off parental duties entirely, sneaking their eggs into other species’ nests. On discovering the intruder, some parasitized birds may break the foreign egg or starve the fledging, while others may haplessly raise the parasitic bird’s chick. At the other end of the spectrum, female Common Merganser “carpool moms” are known to gamely shepherd the offspring of other Common Mergansers, sometimes leading large groups of 50 or more chicks, which require a low level of individual parental care: “it’s relatively cheap,” writes Dr. Tong.

When no open territory is available, older juveniles ready to live independently may stay with their parents—a phenomenon also well known to human parents. These “teenage” birds are not free-loaders, however; they help care for their parents’ next brood of offspring, possibly one day inheriting their parents’ territory.