Flowers, bursting buds on trees and vocal songbirds appear almost as if they were part of a well-choreographed ballet.
Indeed, it is a ballet, and the choreographer is natural selection. But lately the ballet company is in trouble.
Some dancers are falling out of step. The stages on which this traveling company performs for a few days in the spring and fall are disappearing, threatening the very existence of some dancers.
First, the problem with out-of-step dancers:
Plants in our part of the country come to life in the spring in response to seasonal weather changes. As temperatures warm, plants break bud, grow leaves and flower. Insects that feed on their nectar, pollen or leaves soon follow, using the same cues.
Many migratory songbirds, on the other hand, overwinter in tropical regions. They begin migrating to their breeding grounds in response to changes in day length and star positions in the nighttime sky.
Global warming affects local cues used by plants and insects, but not those used by migratory birds. According to NASA, the warm February we just experienced deviated from its normal mean temperature by more than any other month ever recorded. The warmth of spring — and its effect on local plants and insects — comes earlier these days.
Migratory bird species sing and fly onto the local stage much later than they did a hundred years ago. They come on the same calendar date, but not at the same point in the advancement of spring. They are late for that, missing the plants and insects that provide sustenance during their journey.
Second, another problem with the stages:
Migratory birds have fewer places to land and feed in their tropical wintering grounds, their breeding grounds and crucial habitats along their migration routes.
A report in the journal Science in December found that only 9 percent of all migratory birds species worldwide have protected habitats at all points along their migratory routes and their winter or breeding range homes. By comparison, 45 percent of nonmigratory bird species have adequate protected habitats within their home ranges.
The number of protected habitats varies by country, but not necessarily by the wealth of those countries. For example, Latin American countries with relatively low gross domestic products have higher levels of protected habitats for migratory bird species than Canada and the United States do.
Take the cerulean warbler, a colorful summer resident. It overwinters in northwestern South America, migrates through Central America and the southeast United States, and breeds in the Midwest. But the species nests high in treetops of old-growth forests, which are disappearing across the United States.
In 1962, Rachel Carson propelled an environmental movement with her book "The Silent Spring." The first Clean Air and Clean Water Acts followed within three years. Carson focused on the effects of insecticides and other pollutants on birds and other signature species of spring.
Carson never dreamed that those species wouldn’t have a stage on which to appear.
Steve Rissing is a biology professor at Ohio State University.
original story HERE.
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