[1] In the 20th century, coal miners would bring caged canaries down into the mine tunnels with them; dangerous gases such as carbon monoxide would kill the canaries first, serving as a warning to exit the tunnels immediately.
Of all the organisms that ever roamed the planet, more than 99% are extinct. Humans, of course, are not entirely to blame. The five mass extinctions wiped out a great deal of species due to natural processes. But scientists contend that we are amid a sixth one — and this time, it’s our fault.
All the alterations humans have made to the earth are finally collapsing the populations of too many plants and animals worldwide. In the coming decades, thousands of species are projected to disappear forever. The absence of many will take a toll on ecological webs across the globe, dooming even more organisms. Take plants, which produce the oxygen we breathe and make up the backbone of almost all food chains. Sixty-eight percent of the 12,914 species evaluated worldwide are threatened with extinction. All the organisms, including ourselves, that depend on plants for food and survival are automatically threatened.
There’s more. Diminishing quality of aquatic ecosystems are endangering fish, dolphins, whales, and invertebrates. Reptiles can’t find each other through the fragmentations of habitat loss. The fast-disappearing tropical forests are jeopardizing even our closest relatives, the primates. Half of the world’s primates are at risk of extinction. We’re not one of them, but could we be affected by our own medicine?
The answer may lie in a group not yet mentioned: birds. These flying, feathered beings are undergoing some of the most tangible declines of the world, and migratory songbirds in particular seem to be paying the heavy price of our development. Warblers, vireos, thrushes, flycatchers, and more are suffering under habitat loss, climate change, and other unfortunate factors. Their decline confirms profound changes in the environment, and force us to ask: Is this the canary and the coal mine? [1]
The Obstacles of Migration
Consider the cerulean warbler, a tiny sky-blue bird with a bright, buzzy song that breeds right here in Pennsylvania. Cerulean warblers migrate very long distances, from their breeding grounds in eastern North America to their wintering habitat in northern South America. However, not enough to make it there and back. Since 1966, cerulean warblers have declined over 74% in population, and are rare across their range today. Here’s what these 10-gram bundles have to go through on migration:
1. Deforestation: Many cerulean warblers spend the winter in Columbia, where forests are fast-disappearing. 200,000 hectares of forest are lost every year, which not only spells danger for migrants but also for resident tropical species. Here in North America, climate change is pushing the cerulean warbler’s range northward, and there is no guarantee that suitable forests will be found there.
2. Unsustainable Land Use: On migration, stopovers for refueling are critical. Where soil is severely depleted, migrants won’t find anything to eat — for long-distance migrants like cerulean warblers, this is especially a problem.
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