Non-birdwatchers may think of fall migration as taking place in late September when V-shaped flocks of geese start passing overhead, honking as they go. In fact, birds begin heading south in August, after they have finished breeding and gone through their molt.

Here in Wilmot, I start noticing changes in the local birdlife in July. Birds of tropical origin, like the wood warblers and the indigo bunting, stop singing and retreat into the underbrush to exchange their worn-out feathers for new ones before they make the long flight to their wintering grounds. A few of the hardier warblers begin to sing again in August, but it is an abbreviated, less frequent, and less enthusiastic version of their breeding-season song.

On August 24, I saw my first real “flight” of fall warblers. The large deciduous trees behind my cabin, which mark the southeastern edge of a nearly continuous forest of thousands of acres along the Wilmot-New London border, were full of Tennessee and Nashville warblers at 7 AM. 

These birds migrate through the night and then, in order to feed, alight where they find themselves at dawn. The warblers were so hungry they barely acknowledged my existence, chasing insects to within 20 feet of me.

The Tennessee warbler is a sharp looking bird in its breeding plumage, with a gray crown, white stripe over the eye and a black stripe through it, an olive-green back, and whitish undersides. The contrast among all these colors is very much muted in its fall plumage. 

The Nashville warblers are comparatively unchanged by their molt. They are still olive-green on the back and warm yellow below, with a prominent white eye ring.

Neither species was singing at all. Instead, they were making quiet but repeated contact calls to keep the flock somewhat together. There was at least one black and white warbler among them that was singing. 

He may not have been a migrant, but one of our local birds attracted by the hubbub of all the new arrivals. The yellowthroats skulking in the adjacent meadow were certainly locals. I see them almost every morning, but they have long since stopped singing.

I went out again a quarter of an hour later and Merlin identified a pine warbler (which may be a local) and a redstart, which certainly was not. We only see the redstarts during spring and fall migration. They seem to prefer being deeper in the woods, and our cabin is surrounded by a patchwork of woodlot, meadow, and mowed fields. 

Merlin also heard a Baltimore oriole, another species of tropical origin that leaves early, and a swamp sparrow, a bird that we do find locally, but we don’t have in my immediate neighborhood during the breeding season. The latter species points to another phenomenon related to but not the same as migration: post-breeding dispersal. 

Many birds, particularly young ones born this year or those born last year that did not manage to find a mate or establish a territory, will often wander here and there during August and September before departing for their winter destination. Four days later, on my daily morning walk with the dog, Merlin claimed to hear a Wilson’s and a hooded warbler. 

The hooded warbler is probably a “hallucination” on Merlin’s part. Artificial intelligence applications are still prone to this kind of error. This particular species does not breed north of central New York and the very southern part of New England. 

It is possible that one dispersed northward, but not likely. Don’t believe everything Merlin tells you. It is a good app for learning songs but is no substitution for seeing the bird.

I didn’t see the Wilson’s warbler either. Many of the fall contact calls sound very much alike and even the amazing sound library in Merlin cannot always match the right recording to the sound it has just heard. On September 4 another warbler flight came through, bringing more Nashville and Tennessee warblers, but also many Blackburnians, which in the fall are a mere shadow of their flaming black and orange breeding plumage. 

The flock also included two species of vireo and a few other warblers. This will continue through the next few weeks and then they will all be gone until next year. When they arrive from the south in late April and May, they will be just as hungry.