My first job in the South was listening to birds sing. As a lifelong birdwatcher, I've developed the ability to identify most any local bird by sound. All good birders can do this, and it's a skill that allowed me to earn a living one spring by hiking Nantahala National Forest at first light to census the dawn chorus.
In a healthy forest, a dozen species of bird might be singing simultaneously: thrushes, warblers, vireos, tanagers. Dawn sets them off. Once you know the songs, the chorus is a roll call: wood thrush, red-eyed vireo, tufted titmouse, hooded warbler.
To hear some birds, you must visit high elevations or a particular forest type, but many local species occur throughout the forest. Black-throated green warblers seem to be in earshot at all times in our mountains, or it used to seem that way.
"Trees, trees, tall sweet trees," the warbler sings in high, sweet buzzes.
I say it "used to" because this common bird has become scarce. They nest in hemlock trees, which are mostly dead or dying from infestation by tiny, parasitic insects. Rather than switching to a different tree for nesting, black-throated green warblers seem to be disappearing with the hemlocks. On a four-day trip to the Smokies this year, I should have lost count of black-throated green warblers, but I heard only one.
Ornithologists studied how forest birds use hemlock trees and identified four at-risk species: blue-headed vireo, Acadian flycatcher, Blackburnian warbler, and black-throated green warbler. Black-throated greens earned the highest dependency score, twice as dependent on hemlock as the other species. The flycatcher and vireo were abundant on my hike.
It seems silly that the birds do not settle for a second choice tree, but birds have surprisingly precise nesting behavior. Famous studies demonstrated that warblers divvy up nesting habitat by specializing in where they build nests. One species nests in high branches, another low boughs, another along stream banks. Black-throated green warblers use live hemlock boughs to support and camouflage nests.
These warblers also nest in fir trees, so the northern part of their range retains nesting sites. Their prospects are sad but not hopeless. Maybe the warblers will learn to use elm boughs.
However fate crashes over bird, tree and man, ecological decline is a certainty.
Both tree and bird are vulnerable, part of weakening ecosystems.
In his seminal 2004 essay "End of the Wild," MIT economist Stephen Meyer argued, "the race to save the composition, structure, and organization of biodiversity as it exists today is over, and we have lost."
"In the past century we have accumulated a vast extinction debt that will be paid, with interest, in the century ahead." Meyer wrote of "relic and ghost species," populations of plant and animal that linger in isolation but face an inevitable decline toward extinction. The winners in these homogenized ecosystems will be weedy species, "plants, animals and other organisms that thrive in continually disturbed, human-dominated environments."
Poison ivy, rats, and house flies—that is the future of biodiversity.
This extinction debt is based on damage already done. It does not include climate change. That's a wild card thrown on top of a century of industrialization. Whatever hope there might have been for preserving biodiversity, climate change is scrambling the parameters faster than nature or man can adjust. As the seas rise, we can only retreat.
The retreat of the black-throated green warbler happened faster than anyone could have guessed. Everything is connected in nature, and the woolly adelgid pulled on a strand that took down the definitive Southern Appalachian tree, the hemlock. Now it is dragging down a once-common bird. Also along for the ride are fish and aquatic creatures that need shade and cold water.
Inevitably, the strands of connection will work their way back to us, and abstract longing for healthy forests will be replaced by real threats to our economy and well-being.