North American Birds
Turdus migratorius; American Robin. Photo © 2001 John White.
DB: This is Earth and Sky. Common backyard birds – such as cardinals, warblers, robins, and bluejays – are species that were here in North America long before your yard was a yard.
JB: There are essentially no fossil records for these small birds – their bones are fragile and hollow. So it’s only been within the past few years that scientists have been able to estimate how long these species have been around, using molecular DNA technology. Turns out these birds have been in North America for about five million years.
DB: So our common backyard birds species have endured millions of years of cycles that came and went – ice ages, shifting landscapes – as the forests and plains changed shape and size. Ice pushed their habitats south, and warming climates allowed them to push northward again.
JB: But it’s recent changes – since people have been around – that have proven to be the bird’s toughest survival challenge yet. That’s because it’s happened so fast. In just the past two hundred years, the whole face of North American has become radically different. Cities, suburbs and large farms continue to eat up wild habitats. Now, some bird species that have been so adaptable in the face of long-term changes are at great risk of extinction.
DB: That’s our show. Thanks today to the National Fish and Wildlife Foundation and to the Bureau of Land Management. We’re Block and Byrd for Earth and Sky.
The following individual was interviewed for today’s show. Our thanks to:
Dr. Irby Lovette
Director
Evolutionary Biology Program
Cornell Laboratory of Ornithology
Ithaca NY
Author’s Notes:
It’s almost certain that there are many species of birds that didn’t survive that we’ll never know about – that have gone extinct leaving no record at all.
2643 On the one hand, we can realize that they are adaptable, and they have been faced with changing environments over their evolutionary history, and they’ve weathered those changes. And so our job is to watch the changes that we’re making, and try to ensure that they’re not so severe that these species can’t continue to adapt to those changing conditions.
12.42 It’s my hypothesis that active migration actually allows their species to change their ranges relatively rapidly in the face of things like climate change…. Glacial cycles came and went, and the boreal forest was pushed down in the deep southeast of North America. Those species – because they were migrating every year – could perhaps track those changes better than more sedentary species.
22.55 Now we have the situation where as humans, we’ve modified the environment to the point that some number of these species are actually faced with the very short-term risk of extinction, and so by restricting their habitat, by reducing their population sizes, we’ve actually taken species that have been robust in the face of long-term changes and put them at great risk of extinction
