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Monday, July 3, 2017

Back from the edge

Did you know that the Kirtland’s warbler is now a candidate for de-listing as an endangered species because its population has recovered from 167 breeding pairs in 1974 to more than 2,000 today? The news of this conservation success came to me via Living Bird, the magazine of the Cornell Lab of Ornithology.

Singing male Kirtland's warbler--photo USFWS

    The story of this 15-gram bird and its restored summer habitat in northern Michigan is a heartening tale of good will and sound science producing results. It could also be read as a parable for our time.

    The Kirtland’s warbler can only build its nest on the ground beneath young jack pines (Pinus banksiana) no higher than around 12 feet. 

Ground-level warbler nest--photo USFWS

Fires caused by lightning or intentionally set by Native Americans used to result in a steady supply of young trees. Then in the twentieth century, settlers started suppressing wildfire, so the supply of young trees shrank.

    As you can imagine, nesting at ground level means the warblers lose a lot of their young to predators such as squirrels, chipmunks, snakes, feral cats and blue jays. They also can’t tell the difference between their own nestlings and young brown-headed cowbirds.

The cowbird is much bigger than a warbler--photo

     The cowbird mother lays her eggs in other birds’ nests, tricking them into raising her young. Cowbird chicks are bigger than baby warblers and hog the food. Often the little warblers don’t survive. Cowbirds have spread from Midwest grasslands to places like the warblers’ home territory as humans have cleared land and built towns.

Cowbird egg in an Eastern Phoebe nest--photo Galawebdesign

    Heroic conservation efforts started in the 1950s and intensified when the Kirtland’s warbler became one of the first species protected under the Endangered Species Act. Federal and state biologists had to take drastic steps to restore the warblers’ habitat—controlled burns, then thousands of acres of jack pines cut and replanted. They also undertook a major program of trapping cowbirds, so that now few cowbird eggs are found in warbler nests. 

    So these are birds that need to build their nests and lay their eggs at the base of only one species of tree and that can’t tell their own babies from usurpers who scarf down all the insects they bring to feed their young. A set-up for evolutionary failure? At least we can say they were no match for the rapidly occurring changes in their surroundings caused by modern humans.

Human habitat, warbler desert--photo bpbailey

    What can we learn from this? I see two warnings. First, as climate change progresses, we’re going to need to adapt. Extraterrestrials observing us from another planet could draw an analogy between Americans and the warblers. The birds can’t live without jack pines; we seem to think we can’t live without a massive fossil fuel budget. If we can’t adjust to a new way of living, might we join the extinction wave? 

Can we find another way?

     Second, we’ve made radical changes in the natural world, just by expanding our population and taking over land for what we regard as normal, benign purposes. We’re going to need to find a way to make a smaller footprint.


1 comment:

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