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Rock Pigeon, Pine Warbler, Barn SwallowAnswers to readers' questions about colors, feeding, nesting, and hopping vs. walking Contributed by Julie Craves
Published: January 1, 2009
Why do pigeons come in so many colors? — John Rowse, Akron, Ohio
The wild form of the familiar Rock Pigeon (Columba livia), from Eurasia, is a grayish bird with a darker gray head, iridescence on the neck, and two black bars on the wings - a form known to researchers as "blue bar." Pigeons were first brought to North America in the early 1600s.
Introduced populations of wild-type birds have been supplemented by escaped and released domestic birds, which are often bred for the color or ornamentation of their plumage. Frequently, domestic versions of animals revert to their wild type within several generations outside of captivity, yet nearly 30 distinguishable color forms have been noted in feral pigeon populations despite their long tenure in the wild.
Although they are now found all over the continent (and, indeed, the world), pigeons usually occur only in close association with humans, particularly in urban areas. For the most part, pigeons in cities have few predators. Conspicuous color forms do not pose much of an increased threat of predation in urban areas, so they survive to pass on their genes to future generations. It is this relaxed selective pressure that is thought to be a main reason so many color forms persist in feral populations.
For more on color forms of feral pigeons, and how you can contribute your observations, sign up with the Cornell Lab of Ornithology's Project PigeonWatch.
Why do some birds hop and others like crows and pigeons walk? Due to their size? — James Hughes, Woodbury, Minnesota
Habitat is the major indicator of whether a bird walks or hops. Birds that spend most of their time in trees usually hop. It's the most efficient way to move from branch to branch, but the species will often hop even when they are on the ground. It takes a bit more energy for a bird to hop than it does to walk, since the bird has to launch its entire body mass forward. Therefore, birds that forage and spend time in open areas on the ground usually walk.
Hopping and walking can be present in the same families of birds, such as warblers. For example, most warblers hop, but ground-dwelling waterthrushes and Ovenbirds walk.
A lot of species, such as crows or robins, both hop and walk. And then there are many species that can't do either. Hummingbirds change perch positions by lifting off and relanding. Chimney Swifts cling to vertical surfaces but are not known to walk or perch on horizontal surfaces at all.
In grebes, loons, and other waterbirds, the legs are set so far back on the body that the birds are extremely awkward on land and are easily stranded if they become grounded away from water.
A yellowish warbler came to my suet feeder recently, but I was unable to get a good enough look to identify it. Do any warblers come to feeders? — Ross Good, Mechanicville, New York
It sounds like your guest was a Pine Warbler (Dendroica pinus). While other warbler species may show up at feeders on rare occasions, Pine Warblers are known to do so regularly.
Not only will they indulge in suet, but they will also eat seeds, as their natural diet includes pine seeds. Millet, cracked corn, sunflower seeds, peanuts, and peanut chips have been noted as feeder fare for the species.
Pine Warblers are quite hardy, and they winter primarily in the southeastern United States. It's not unusual for them to arrive in the north very early in spring and to linger from fall into early winter, coinciding with times when people have active feeding stations.
Barn Swallows nest in the rafters of a local parking garage every year. Most of the nests seem to face north. Since the garage is partially underground, the nests wouldn't be affected by sun or wind, so why do they orient the nests this way? — Shelley Hyatt, Toronto, Ontario
A number of factors may influence the placement of the nests:
Does the site give the birds a direct flight path in or out, or a wider view of the immediate area?
Is there a difference in the surface of the wall that might make it easier to adhere a nest?
Is there less disturbance or commotion under, near, or even in the wall (such as vibrations)?
I located only one study on the topic, and it found no systematic difference in the compass direction in which nests are oriented. It's likely that one or more of the factors I mentioned affect where the swallows place their nests. |
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