Male and female birds are often quite different. Looking at two individuals of radically different color, it’s sometimes easy to forget this.
I often talk to people who think they have multiple kinds of hummingbirds or finches in their yard, when really they are just seeing male and female birds of the same species. Why are they so different? How come sometimes they aren’t? Asking these questions can lead you into all kinds of interesting stories about how different birds lead their lives.
The most obvious differences are in plumage. When there is a visible difference between the sexes, males are almost always more colorful and ornate. Sometimes this is obvious; male house finches are red, while females are brown and streaky. Male turkeys have alien blue and red heads and enormous fanned tails, while females are brown and lack the ostentatious appendages. Sometimes it is more subtle; dark-eyed juncos and spotted towhees share the same basic pattern in both males and females, but males generally show more contrast, with darker blacks than females.
Why is this? The standard explanation is that females rely strongly on visual cues in choosing their mates. Birds that are bright and colorful must be healthy and well-nourished, both for the direct production of the healthy plumage and because such visible displays make them more vulnerable to predators — vivid plumage is functionally a handicap, so if a bird is surviving and thriving while drawing so much attention to itself, then it must be strong and capable.
Female birds, in contrast, typically have a strong evolutionary motive encouraging them to camouflage and discretion. They typically take the lead in incubating the eggs and brooding the chicks, activities in which cryptic, obscuring plumage is invaluable.
There are other differences besides color. Male and female birds can vary in size. In hawks and owls, females are typically the larger of the pair. There are a few hypotheses as to why this is the case (maybe the extra mass is beneficial for laying large eggs or for fat reserves during nesting when foraging time is more limited), but the branching of weights often works out well for both, allowing each member of the pair to specialize in prey of slightly different size, maximizing their hunting efficiency in a given area.
As we enter into the spring nesting season, the most significant differences in the behavior of male and female birds become visible. Males do things to impress females, showing off their health, strength, speed, intelligence and parental instincts.
How do birds show all of this? The two most widespread male behaviors of spring are territorial aggression and singing. Guarding a breeding territory and chasing off other males demonstrates strength and defensive capability directly. Singing takes stamina (health), warns off other males (part of territorial defense) and can also be complex and musical (intelligence).
Other courtship displays are more varied among different species. Male hawks and hummingbirds perform visual displays with dramatic swoops and dives, male house finches offer courtship feeding where they give food to females as they would to babies, and male wrens and mockingbirds construct multiple crude nests for females to inspect, approve and complete (males are better at construction than interior design).
What do female birds do? Typically, the bulk of the work. In the majority of species, females take the lead in nest site selection and construction, incubation of the eggs and brooding of the young (though all of these can be shared). In some birds, notably including hummingbirds, turkeys and ducks, males provide no parental assistance at all.
Then there are birds whose plumage and behavior are markedly less divergent. In the backyard, some examples include crows, jays, titmice and California towhees. What is the common trend among these birds? Long-term pair bonds.
As I described, the root of most of the male-female differences in birds is found in courtship and mate selection. With many birds, including the majority of songbirds, pairings only last a season, and a new mate needs to be found each year. But for birds that maintain their pair bond for many years, there is less need for rapidly demonstrating one’s worthiness through plumage, song or other male extravagances. And so the plainest and most well-matched birds are often those that stick together.
Jack Gedney’s On the Wing runs every other Monday. He is a co-owner of Wild Birds Unlimited in Novato and author of “The Private Lives of Public Birds.” You can reach him at jack@natureinnovato.com.
