During nesting season, I often see a male bird closely following his mate. He may fly where she flies, feed where she feeds, trail after her as she builds her nest, and keep her in view. I see such mate-following in many species: a male mourning dove flying a few inches behind his mate, a male robin staying close to a female hunting worms on a lawn, a male hawk perched next to his larger mate, a male house sparrow keeping airborne pace with a female carrying a bill-full of nesting material. Such classic greeting card images are the kinds of behavior often considered enchantingly sweet.
Isn’t that sweet? Maybe not. I don’t know if any bird feels something like the emotions evoked by the word “sweet,” but, even if a bird shares those feelings, I doubt that much of the association of male and female in the breeding season qualifies for sweetness. The timing of mate-following provides a clue to the function of the behavior.
This avian togetherness is most apparent during nest-building and egg-laying. Why then? If birds are friendly and cozy, why not be friendly and cozy all year?
The nature writer John Burroughs, a sharp observer of birds, also watched males attend closely to females. In his 1913 book “The Summit of the Years,” Burroughs described a male wood thrush watching his mate build a nest as “a bird of leisure” and “a gratuitous superintendent of the work” of nest-building.
These wordings suggest that Burroughs saw this behavior as laziness.
Is the male a lazy sidewalk superintendent? My observations suggest that the male bird is neither lazy nor at leisure. He energetically follows the female, sometimes twisting and turning in flight to keep close; if she leaves his sight, a flurry of vocalizations often functions to bring them back in view of each other.
In recent decades, observations of individually marked birds of many species have revealed a clearer picture of why males stay close to their mates during breeding season, with neither laziness nor sweetness suggested.
Although most birds associate in male-female pairs during breeding season, many birds copulate with individuals other than their mates, and the young in a nest are often the genetic offspring of more than one male.
The state bird of Massachusetts, the black-capped chickadee, provides an example of this phenomenon. Over years of observation, ornithologist Susan Smith, now retired from Mount Holyoke College, saw female chickadees leave their territories and copulate with males other than their social partners.
In each case the female copulated with a male that ranked higher than the female’s mate in the dominance hierarchy of access to food in the local winter flock of chickadees.
More recently, researchers at Queen’s University in Ontario showed with molecular paternity testing that some chicks in black-capped chickadee nests are fathered by males ranking higher than the male associated with the nest, confirming Smith’s findings.
Considering these observations, biologists now interpret a male’s close attention to his mate as mate-guarding, an attempt to ensure that his reproduction is maximized and that he does not put effort into caring for other males’ offspring.
With the modern understanding of why male birds of some species stick close to their mates, some might interpret their behavior using words like jealousy, clinginess or stalking.
As with sweetness or laziness, though, it is inappropriate to apply such words to other species.
It would be difficult, perhaps impossible, to determine whether a male bird subjectively feels jealous or a female bird feels crowded. As understanding of bird behavior changes, uses of birds as symbols in poems or on greeting cards might change, but such use has more to do with human expression of emotion than with whatever conscious feelings a bird might have.
In addition to suggesting laziness, John Burroughs described the male staying near his nest-building mate as “an interested spectator.” The word “interested” was closer to current understanding than Burroughs could have guessed a century ago.
The male indeed watches out for his genetic interests, attempting to ensure that copies of his genes get into the next generation. As Burroughs said, “admiring glances that we cast upon nature do not go very far in making us acquainted with her real ways. Only long and close scrutiny can reveal these to us. The look of appreciation is not enough; the eye must be critical and analytical if we would know the exact truth.”
David Spector is a former board president of the Hitchcock Center for the Environment and teaches biology at Central Connecticut State University.
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