This is Bird Note.

On a fine May morning in Great Smoky Mountains National Park, a song issues from within a rhododendron thicket.

But try as you may, you can't see the singer.

It sounds like a warbler. Many breed in this lush mountain habitat, black-throated

blue warblers, for example. American Red Starts and hooded warblers. But no, it's a Swainson's

warbler, one of North America's shyest birds.

Small and brown, these birds forge quietly on the ground,

flipping over leaves to expose and capture insects.

They scurry away, calling an alarm when big-footed humans invade their shadowy habitat.

They're amazingly good at disappearing in rapid flight through the tangled understory.

On their wintering grounds, in the Blue Mountains of Jamaica, they're even harder to find because they don't sing in winter. There, instead, you might hear a Rufus-throated solitaire singing in the dense

mountain forest. Swinzen's warblers do, however, respond aggressively to a recording of their own song.

That's how ornithologists confirmed the presence of these elusive warblers

and discovered a vital connection between the two mountain forests a thousand miles apart.

For Bird Note, I'm Mary McCann.