The National Audubon Society just released a new report on the effects of climate change on birds, and the results are startling, if not entirely surprising to those of us in the field. Smaller papers and reports have delivered similar findings for individual species, but this report is the first one to encompass all of North America's avian residents.
The gist: as the climate warms up, birds will move up and north.
One of the ways we monitor climate change - and the general health of the environment - is to monitor 'indicator species'. The animals tend to be small; not only do pollutants affect them first and most severely, small body-size also means they have a harder time maintaining their internal temperature (both cold- and warm-blooded) and are therefore more sensitive to changes in climate than their larger relatives.
Animal indicator species fall into two general categories: sedentary and mobile.
Sedentary animals are animals that don't tend to disperse very far from where they were born, either because of their physiology (they can't) or their behavior (they 'choose' not to). The indicator species in this category are mostly amphibians, small frogs and salamanders. They can't disperse much, they're cold-blooded and freeze-intolerant, and they respire through their skin, making them extremely vulnerable to environmental pollutants and toxins. If their habitat changes rapidly (either the climate or the habitat itself), the population has no recourse and goes extinct.
Mobile animals do disperse a fair distance from where they were born, and some (like some birds) migrate seasonally on continental scales of thousands of miles. Birds are warm-blooded, but small birds still have many of the same thermoregulation problems as cold-blooded animals. Keeping warm is just harder to do when you're small. However, since small birds are highly mobile, even if they aren't generally migratory, their populations tend to shift rather than die out.
We can measure both local extinction rates in amphibians and species range shifts in birds, and these give us clues to climate change.
Anyone who has done field work with either amphibians or birds has probably noticed both of these effects, at least anecdotally. We can't find amphibians where we usually find them. Common birds are suddenly nowhere to be found and species generally classified as 'rare' or 'vagrant' are suddenly everywhere (see my ABO 2011 season summary), with a general north-ward trend.
The National Audubon Society's website has excellent interactive maps (this excites me because I'm a GIS geek) showing predicted future species ranges for the several hundred at-risk species in North America, as well as a good FAQ section. The Huffington Post wrote a nice summary, and the full report is here.
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