The birdsong I heard along a trail beside the Owasco River in early May sounded more like a brisk, buzzy “Zee Zoo Zee”, with a drop on the “Zoo” and a rise back to “Zee”, before starting over. It was a Black-throated Green Warbler (BTGW), high in the trees where the tiny, hyperactive warblers like to forage above prying human eyes. Birders learn to identify birds like these by sound, and often learn a specific song with a phrase they can remember. I was charmed to find that “Trees trees I love trees” works for some birders to identify Black-throated greens.
This warbler doesn’t just love trees; it loves eastern hemlocks. The Owasco Watershed Lake Association (OWLA) loves the hemlocks, too. As many Citizen readers know from past articles, this beautiful evergreen, the third most common tree in our Finger Lakes region, is under severe threat by an invasive aphid-like insect, native to Japan, called Hemlock Woolly Adelgid (HWA). Hemlocks are crucial to water quality in our lake, so for several years now OWLA has been supporting Cornell University’s New York State Hemlock Initiative. Trained OWLA volunteers, including me, have surveyed properties all through Owasco Lake’s watershed searching out hemlocks and recording their health. Our data has helped licensed foresters treat and protect watershed critical trees.
I have witnessed the beauty of ravines carved deeply by clear streams that flow downhill to Owasco Lake. I have made my way down to those streams under the deep shade of tall, airy hemlocks where mosses, ferns, trilliums, and wood asters grow. Hemlock roots help prevent soil erosion from the steep slopes into the streams; their canopy creates a cooling, humid microclimate where water temperatures and lack of turbidity are optimal for young trout and salamanders.
I have also seen heart-breaking landscapes. On recent walks in Fillmore Glen State Park in Moravia at the southern end of Owasco Lake, and at Great Gully Preserve on the eastern shore of Cayuga Lake in Union Springs, many hemlocks showed the tell-tale pale, gray-green color and thin foliage of HWA infestation. Others had already died. Anywhere I could reach their foliage to check, it was loaded with HWA. I wonder what our lovely glens and ravines, so symbolic of the Finger Lakes region, will look like in ten years, and beyond? As the foundation species for these ravine ecosystems and in other areas, hemlocks provide food, shelter, and habitat for over 1000 insect species and 120+ vertebrate species, including 96 bird species. One of those is the black-throated green warbler. When the threat to hemlocks feels overwhelming to me, it helps to focus on a single aspect of the crisis. A five inch long, 1/3 of an ounce songbird with a bright yellow face, rich black throat, green back and black-streaked breast fits the bill nicely.
Black-throated green warblers do best in large forests with mature trees. These warblers search on the bark and undersides of twigs for invertebrates, including hairless caterpillars, spiders, gnats, and beetles. They build their nests close to the tree trunk, usually where a branch has sub-divided into a forked base that supports the cup-shaped nest. Although they can nest and forage in other trees, their wellbeing seems closely tied to the presence of eastern hemlocks. They are vulnerable to forest fragmentation. Where hemlocks have died because of HWA, associated black-throated green warbler populations have vanished. Scientists consider the black-throated green warbler to be an indicator species for hemlock forests. If they are found in a mature hemlock stand or a mixed evergreen and deciduous forest, chances are the ecosystem is healthy.
My encounter with the black-throated green warbler this spring happened in open deciduous woods where these little birds don’t typically live. May is migration time for warblers and other birds. This one most likely was headed for hemlock or spruce forests farther north, although the Finger Lakes lie within the southern edge of the BTGW’s breeding range. Researchers are aware that, as hemlock trees disappear from New York State because of HWA, black-throated green warblers may become regionally extinct.
When I think about that, I remind myself that the little birds can be somewhat flexible with where they feed and nest, and that the species is readily found nesting across the central and eastern half of Canada and the United States. This gives me hope for the resilience of this one bird species. They are part of the larger story whose telling depends in part on the fate of hemlocks. OWLA will keep supporting the scientists working to save hemlocks here. I hope I will hear a black-throated green warbler on another walk near Owasco Lake next spring.
Julie Lockhart is a member of the board of directors of the Owasco Watershed Lake Association. For more information, or to join OWLA, visit owla.org.
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