Friday, May 16, 2008


BRITANICA BLOG All over North America, populations of songbirds are declining. They have been doing so for the last couple of decades, to an extent that is alarming because, to make a poor play on words, songbirds are the proverbial canaries in the great coal mine that is the environment. The causes for the decline are imperfectly understood, but, increasingly, scientists are seeing it as a perfect storm of multiple causes.

Some of those causes are on a global scale. Because of climate change, for instance, there have been more hurricanes in the Atlantic basin, and these have tended to be more intense than hurricanes of past eras. Some scientists theorize that songbird populations in eastern North America are in decline because, as the songbirds migrate over open water, they are felled by violent squalls. Literally millions of migratory birds that cross the Gulf of Mexico are thereby at risk. Coastal breeding grounds, migratory stopovers, and wintering grounds are similarly threatened by rising sea levels. A recent National Wildlife Federation report ventures that rising temperatures and habitat loss mean that species such as the blue-headed vireo and the purple finch may soon be absent along the eastern seaboard.

Another cause of the decline may be the global problem of mercury pollution, which has increasingly turned up at high levels in songbirds under autopsy. Today a full third of the lakes in the United States are so polluted with mercury that warnings have been issued against eating fish taken from them. One-half of that mercury, it is estimated, comes from China, whose factories and power plants release nearly 600 tons of it into the atmosphere every year, along with 22.5 million tons of sulfur and other pollutants. The International Energy Agency predicts that China will account for more than a fifth of the growth in world energy demand in the next 25 years and for more than a quarter of the increase in greenhouse gas emissions. This means that its contribution to the mercury problem is likely to rise, whether North American producers do anything to reduce emissions or not.

An increase in monocultural agriculture-the planting of a single crop across vast areas-has reduced available habitat for many songbird species in all parts of the country. In the South, cotton growing is again on the rise; not only do the huge quantities of pesticides and herbicides used poison the birds, but the intensive plowing and flood irrigation also destroy habitat for the Eastern meadowlark, the bobwhite quail, the grasshopper sparrow, and other passerines. The conversion of huge tracts of land to corn production for ethanol-an intolerable waste of energy on other grounds-has similar effects in the Midwest. In South and Central America, the winter destination for many migratory species, forests and meadows are being cleared for the monocultural production of such crops as coffee and grain, the latter mostly to feed cattle. Couple these uses with the housing developments, industrial sites, and commercial zones that are taking the place of wildlife habitat to serve another monoculture-the exploding human population, that is-and the songbirds have few places left to go.


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