A Golden-winged Warbler passes through Sewickley Heights

A Golden-winged Warbler (Vermivora chrysoptera) spent at least a few days in Sewickley Heights Borough Park at the end of August, first reported on August 26 and logged on four separate checklists over the days that followed, never more than one bird at a time.¹ It was moving through with the first real push of fall migrants; two Cape May Warblers were in the same park on August 21, and Yellow-bellied and Olive-sided Flycatchers have followed into the first days of September.¹

It is a small, sharply marked warbler, easy to name if seen well. The male is soft gray above and clean white below, with a black throat and a black mask through the eye, both edged in white, and a patch of bright yellow on the crown and another on the wing. The female wears the same pattern in gray where the male has black. The bird it gets confused with is its close relative the Blue-winged Warbler, which is yellow-bodied with a thin black line through the eye and two white wing bars. The two interbreed freely where their ranges meet, and the offspring, known as Brewster's and Lawrence's warblers, mix the parents' markings in ways that keep birders honest. A fall bird in these hills calls for a careful look at the throat and the wing.

Watch one feed and its way of making a living is plain. Golden-wings probe curled, hanging dead leaves in the understory, often dangling upside down like a chickadee to reach inside for caterpillars and spiders. That dead-leaf specialty is why the bird turns up low in shrubby edges and tangles rather than in the canopy, and it is a useful habit to know in fall, when a quiet bird working a leaf cluster is more likely to catch the eye than one that is singing.

What the species needs to breed is young, shrubby ground: the regrowth after a clearcut or a burn, an old field filling in with saplings, a shrub swamp, a utility right-of-way. That is a habitat that does not last. Left alone, a shrubland grows into a pole-stage forest in a decade or two and the warblers leave. Golden-wings once bred across the Appalachians, Pennsylvania included, and their retreat from this part of the range has two well-documented causes: young forest that has matured or been developed, and the Blue-winged Warbler, which moves into the same openings, competes for them, and hybridizes with the Golden-wings that remain. Roughly seventy percent of the world's breeding Golden-wings are now in the upper Great Lakes states and Manitoba. The species is on the federal list of Birds of Conservation Concern, tracked but not listed as endangered.²

A bird here at the end of August is on its way from wherever it nested to wintering grounds in Central America and northern South America, feeding in whatever cover the route offers. Sewickley Heights Borough Park, 1,005 acres of borough-owned woods and edges open to the public, is one such stopping place, and the next few weeks are when the rest of the warblers will be passing through it.³