This article was updated on Oct. 7, 2023.
EASTHAM — When cold northern air pushes into New England in the fall, it carries with it waves of warblers. These tiny songbirds migrated through our woods and parks in the spring and spent the summer raising their young in the northern forests of Canada. Now, from late August through early November, they fly by again on their way to the tropics.
Warblers here in the spring move fast, with whole species appearing and disappearing within a few weeks. Fall warblers tend to move at a more leisurely pace. Some of these species can be found on the Cape for months as they slowly make their way south.
The National Seashore’s Fort Hill Trail in Eastham is one of the best places on the Outer Cape to catch these birds during their fall migration. On a cool morning, right after a night of steady winds out of the northwest, I bundled up in a sweater and warm hat to visit this site and see what warblers had flown in overnight. Most songbirds migrate at night, eating and resting during the day. Walking the edge of the weedy field at the center of Fort Hill, I quickly got lucky: among the first feeding flock of birds I saw was a handful of warblers.
These did not seem like the warblers I had seen in April and May, however. Warblers in spring are big vocalists, announcing their presence with loud, rolling songs. These warblers were quiet, barely uttering more than the occasional “chip” or “zeet.”
The first thing that a birder will notice, though, is their radically different look. Spring warblers are among the most beautiful birds on the planet. Oranges, yellows, and blues, sharp contrasts, clean lines — male warblers in the spring look like they were designed by some heavenly artist; their bright patterns will help these warblers secure a mate up north. But in the fall, there is no need to attract a female. The warblers’ colors fade, and their bright plumage is replaced with gray and brown feathers.
At Fort Hill, a male Blackburnian warbler — the same species that in spring has a stark black-and-white back and a flaming orange throat — was more muted, its orange replaced by a dull yellow. A male northern parula, a tiny warbler, had clearly undergone a similar transformation. Its slate blue back and sunburnt ochre breast were replaced with grayish upper parts and a splotch of yellow.
The transformation is not so extreme for all warblers, though. Nashville warblers keep their yellow with gray hoods into the fall, with the colors just a little bit faded. But most of the warblers I encountered at Fort Hill looked starkly different from their spring counterparts.
No bird looked more different than the blackpoll warbler I watched foraging in a spruce tree. This bird in the spring is covered in beautiful black and white streaks running down its body. In the fall, it’s as drab as can be: brownish wings and a brownish-yellow body do little to distinguish it from other warblers. But this plain plumage hides an extraordinary adaptation that is unique to fall blackpolls.
In spring, these warblers race up the continent with the rest of the warblers, making their way to their breeding grounds as fast as they can to secure the best territory and resources. In fall, these birds have a different strategy. They fly to a spot near the coast, like Cape Cod, and begin feasting on insects. For some time, they will do nothing but eat. After a while, each bird’s underbelly bulges with yellowish fat. They often double their body weight during this time.
Then, they launch themselves over the ocean. These birds — who, mind you, only weigh as much as a pair of nickels — will fly south for upwards of 72 hours, not stopping once between New England and South America. They cover a distance of 1,500 miles without eating, drinking, or sleeping, subsisting on their fat and muscle reserves.
Why they’ve adopted this particular strategy is a mystery. But it is only in the fall, without the need to rush to the breeding grounds, that these warblers have time to prepare for a journey like this.
Most of the warblers that visit the Outer Cape migrate slowly in the fall, devouring bugs at stopover sites and moving on when the wind is right. Without the need to find a mate, there is no need to sing and look flashy, and they save energy by not developing the bright pigments that make them so beautiful in the spring. One of my friends likes to refer to these birds as “warblers in pajamas.” That is, they don’t have anyone to impress, so they put on comfortable plumage and lumber their way down the continent.
Some people might be disappointed by how plain warblers can be in the fall, at least compared to their spring resplendence. But this is a cozy time of year, when the Outer Cape settles down after a busy summer, when we spend a whole holiday eating, when people don warm sweaters and fuzzy mittens to enjoy the crisp fall weather. Who am I to judge warblers for getting comfortable, too?
Editor’s note: A previous version of this article, published in print on Oct. 5, included the adult male American redstart among the examples of warblers that change their plumage dramatically in the fall. That is not true; the adult males retain their black-and-orange plumage in the spring and the fall. That example has been replaced with the Blackburnian warbler.