Williamsburg, Va.

THIS month is the peak of spring bird migration, when New Yorkers flock to Central Park, craning their necks to catch a glimpse of refueling warblers.

But the treetops hold fewer feathered gems each spring, to the point that a typical middle-aged bird-watcher now feels triumphant upon seeing a single bay-breasted or Canada warbler, two of the dozens of disappearing species common in our youth.

Humanity’s assault on migratory birds includes a familiar litany of human-made perils — clearing of forests, predation by cats and poisoning by the toxic byproducts of agriculture and industry. But one of the biggest contributors to the decline in migratory bird populations has gone largely unnoticed: white-tailed deer.

By 1900, deforestation and unregulated hunting had reduced deer populations in the Eastern United States to tiny remnant clusters surviving in remote sanctuaries. But subsequent protective laws and aggressive habitat management allowed deer to bounce back.