Part One (of Three)
Since we’re getting to the colder months, we thought it would be a good idea to discuss migration. There’s a lot of ground to cover on the topic, so we’ve broken it into three separate articles. This is the first.
Nearly every bird species migrates to some extent. The two main reasons they’ll move from one location to another are: 1) food; and, 2) nesting locations. Most birds that nest in the Northern Hemisphere migrate northward in the spring to take advantage of plentiful full-foliage nesting locations, as well as flourishing insect populations and budding plants.
As winter approaches and insects and other food becomes scarce, those same birds move south again. Lack of food is why any bird that typically eats insects, like flycatchers and swallows, are migratory. And it’s why fruit eaters, like orioles, and birds that get nourishment from flower nectar, like hummingbirds, also need to migrate.
Birds that generally stay in the same or a nearby locale include species that eat seeds or grain—pigeons or doves; or eat insects that hibernate in trees—like woodpeckers; or eat meat—like hawks and owls.
There are four categories of birds when you talk about migration. They are broken down by distance traveled:
Resident birds are able to find adequate supplies of food year-round.
Interestingly, the “resident bird” label may be only true in specific locations. Many birds that are considered resident birds in the continental United States are considered migratory species throughout Canada and Alaska.
Also, some birds that are year-round residents of Florida, Texas, and other southern states may be considered migratory birds elsewhere.
Short-distance migrants move a distance that can be measured in miles or fractions of miles. It can be as little as moving between a higher and lower elevations on the same mountainside.
Medium-distance migrants cover distances in the hundreds of miles. In the United States that could encompass traveling from one state to another or, at most, a few states away.
When we think of migratory birds, we’re usually thinking about long-distance migrants.
The term long-distance migrants refers to the birds that move from breeding ranges in the United States and Canada to wintering spots in Central and South America, a distance that can be measured in thousands of miles. Of the more than 650 species of North American breeding birds, about 350 are long-distance migrants.
Why Long-Distance Migration
Scientists speculate that while the shorter migrations of the first three groups most likely developed from temporarily relocating to areas with greater food resources, the origins of long-distant migration patterns are much more complex.
They believe that seasonal long-distance migration evolved over thousands of years and is controlled at least partially by the genetic makeup of the birds. They also consider the possibility that responses to weather, geography, food sources, and day length, may be among other factors.
Come back next Wednesday when we expand on the fascinating story of long-distance migratory birds.