Birds have developed a wide range of behaviors related to courtship, mating, nesting, and brood raising. In this lesson, we’ll explore a few of these variations. Ornithologists often assume each of these differences is somehow related to the success of the species (natural selection). But I, for one, believe some differences just appear by chance and provide no benefit or no detriment. Maybe some behaviors are perpetuated just because they are fun, or at least enjoyable.
As a birder, we use these behavioral differences to locate and identify birds. For example, the territorial song of a male in the spring helps us look in the right direction to see the bird. The song also helps us to know what image to look for. We don't look for a Great Blue Heron if we are hearing a Bullock's Oriole.
A bird's survival is often linked to how well it blends in with the environment but the finding of a mate often requires more visibility. In late March or early April, I can almost guarantee seeing a Sage Grouse at daylight on the same lek that has been used year after year. I wonder if a Golden Eagle remembers where this lek is and makes arrangements to have an easy breakfast whenever hungry. Other species, like the Virginia Rail, can be very hard to find even at the peak of the mating season. Maybe the best way to approach this subject is to discuss a few examples and speculate on why specific behavior patterns work for certain bird species.
One of the most curious behaviors is displayed by the Wilson's Phalarope. In northern Utah, we observe these birds mostly during the migration period. The Wilson's Phalarope is the primary reason the Great Salt Lake (GSL) is designated as a Western Hemispheric Shorebird Reserve as over one-third of the world's population depends on the GSL for feeding during migration. The female Wilson's Phalarope is larger than the male and more colorful during the breeding season. The females select a mate, breed, select a nest site, and lay a clutch of eggs and then the males are responsible for incubation and brood raising. After the first clutch of eggs are laid, the female selects a new mate and repeats the process. This behavior allows the species to produce multiple clutches during the short summers of the arctic.
Most passerine birds and other species with altricial young (undeveloped at hatching) require food delivered by both parents to live. The Bullock's Oriole provides a good example. The males arrive at the summer range a few days before the females. The male establishes a territory and protects it vigorously from rivals. A strong pair bond develops after a female has selected the males territory. Bullock's Orioles are noisy with much singing and chattering. The male Oriole's bright colors and complex song make it a favorite among birders. Once the pair bond is established the birds build a sturdy, tightly woven, cup-shaped hanging nest. This nest is quite different than the cup-shaped American Robin nest or the flimsy platform used by Mourning Doves. The depth of the Oriole's nest seems to provide protection from many predators and from Cowbird eggs. Both parents will feed the young and will often be assisted by an immature (first year) male. It is believed that these male assistants are from the previous year's clutch.
The instinct to feed young is strong. Many records exist of birds feeding the young of a different species or the yo
ung from a different family. John Bellmon and I once located an aspen tree with a cavity housing Tree Swallow young only about two feet from a cavity with a brood of House Wrens. When the adults brought food to the young, they often entered the wrong hole and fed the young of the other species.
One of my favorite courtship behaviors is that of the Western and Clark's Grebe. The male will acquire food items and present then to the female. As the pair bond strengthens, the pair will perform a synchronized dance routine consisting of much head bobbing and then a side-by-side run across the water. I've observed a pair with a brood where the male would catch a small fish and give it to the female. The female would then feed the fish to the young that were riding on her back.
Almost every courtship and mating behavior imaginable can be found in some species of bird. Cowbirds are polyandrous -- each female is courted by several males. They lay their eggs in other birds nest so they do not participate in any nest building, incubation, or brood raising activities. Red-winged Blackbirds are polygamous with several females for each male. Canada Geese are monogamous -- the pair bond often lasting for a lifetime. Generally speaking, both male and female will feed and care for altricial young, but only the female will care for the young in species with precocial young (capable of mobility shortly after hatching). Oriole's defend a territory large enough to provide adequate food for the adults and young. American White Pelicans are colonial nesters with a very small territory around each nest. Pelicans often fly long distances for food -- the “kitchen" being a long way from the "nursery." Sage Grouse rely on the females visiting the lek for mating, whereas a Black-headed Grosbeak male will rely on his singing and territory protecting abilities to attract a mate.