Don’t look now, but there are some weird mating rituals going on under your very nose. Birds are hooking up in morally reprehensible ways. By human standards, birds can be exceedingly naughty. Take hummingbirds, for instance. Total promiscuity among birds is rare, but hummingbirds are famous for one-night stands, after which they don’t even bother to exchange phone numbers. There is no social relationship before or after coupling, not even dinner and a movie.
Most bird species are monogamous, or at least that’s what we used to think. DNA testing has revealed that even birds in committed relationships are not above sneaking off for a quickie. The Maine state bird is a perfect example. Black-capped chickadees are socially monogamous, which means that they form pair bonds and raise broods together. But all of the offspring in her nest might not be his. Often, according to DNA tests, they’re not.
Mother Nature favors breeding strategies that best perpetuate the species. For most birds, that means a pair bond in which nestlings are raised by two industrious parents. However, the wayward female chickadee increases the odds of her genes being passed along if she spends a couple of romantic minutes with the boy next door, adding a little genetic diversity to her family and hedging her bets.
Since male chickadees are also sneaking next door, diversity is enhanced for him, too. Meanwhile, the parents remain faithful to their brood-raising chores, if not to each other. At least for the female, she can be sure that the youngsters in her nest are hers.
Some species engage in egg-dumping, whereby the female lays her eggs in the nests of her own kind to be raised by an unsuspecting foster mom. In some cases, it’s another strategy to spread genes successfully. In other instances, it may be a desperate means of starting a family when there aren’t enough quality nesting sites or food resources to go around. It certainly happens more often when there are more opportunities. Where nest boxes are overly concentrated in one area, wood ducks will dump their eggs in other nests more frequently.
Barn swallows nest colonially under barn rafters. Females must be vigilant in guarding their nests or surely they will return from feeding to find eggs they didn’t lay.
Some birds do mate for life and show little evidence of wandering. Generally, this has less to do with high romantic ideals and more to do with successful breeding strategies. Geese, swans and eagles are well known for long bonds. But, in each case, the investment in raising young is extensive. It takes over a month just to incubate a bald eagle egg, and raising the young takes many months. A hefty workload requires two parents. Long-term partnerships are essential if either parent is going to pass along genes to the next generation. Much like eagles, geese require long-term pair bonds to get the child-raising accomplished. But there is another motivation, too. A gander who wanders off in search of alternative affection leaves his own mate alone, vulnerable to the attentions of other males. Loser.
Some smaller birds appear to mate for multiple seasons, especially among species with relatively short migration patterns. For instance, robins and doves have demonstrated fidelity for multiple seasons. Long migrations are dangerous and require too much individual effort, so fidelity in most migrating species is unlikely. In any case, even among birds that “mate for life,” if one partner perishes, the grieving period for the other will be short — about the time it takes to read this sentence. If a bird appears to grieve longer than that, it may be confused rather than woeful. In the bird world, there’s no time for sentimentality.
Other breeding strategies certainly have an influence on bird monogamy. About 13 percent of species are colonial nesters. They group together for protection and to maximize scarce breeding habitat. Herons often nest in large groups, habitually on islands or in wetlands where they are safer from predators.
Terns nest together on remote islands where they are secure and can mob intruders. The Florida scrubjay is endangered because of diminishing habitat. But because this habitat is already so scarce, small groups join together to protect a mutual breeding territory. Newcomers have to earn their space by helping. I can only imagine the social dynamics.
But this is all rather tame philandering, not much different than late night cable television. The real kinky stuff is coming up next week.
Bob Duchesne serves as a Maine Audubon trustee and vice president of its Penobscot Valley Chapter. Bob developed the Maine Birding Trail, with information at www.mainebirdingtrail.com. Bob can be reached at firstname.lastname@example.org.