Blackpoll Warbler

If you’re inclined to hike in the high-elevation Spruce Fir Forests in the White Mountains, chances are you’ve at least heard a Blackpoll Warbler. Along with juncos and White-throated Sparrows, this warbler is one of the most common birds in this habitat. Farther north it also breeds in lowland spruce forest, where its range extends from the Bering Sea in Alaska across the vast Canadian taiga to Newfoundland. An estimated population of 60 million birds make the Blackpoll one of the most abundant birds in North America.

Its abundance and wide range, however, are not what makes the Blackpoll Warbler stand out. For that we need to turn to the species’ migration route. Each fall most of those 60 million Blackpolls head south and east towards the coast of the Northeast U.S., where they will stop to rest and feed for up to two weeks. When they arrive they weigh less than half an ounce, but can almost double this weight by feeding on berries and insects. Once fattened up, they wait for a northwest wind and head out over the North Atlantic. Unless they die on route (and many do) their next landfall is 80 hours and 2000 miles later somewhere in the eastern Caribbean. Physiologically this is a feat that we mere mammals can barely comprehend, let alone achieve.

After wintering in South America, Blackpolls have a much easier route in spring. They make a shorter water crossing over the western Caribbean to land in Florida or along the gulf coast and then spread out to work their way back to their breeding grounds over land. Add all this together and the birds that breed in Alaska have one of the longest migrations (potentially 13,000 miles) of any North American songbird.

Migration is a dangerous time, and migratory species are more likely to be declining than sedentary ones. The Blackpoll Warbler is no exception, and may be only half as common as it was 50 years ago. Because most of them breed in remote northern forests the possible causes of the decline are largely unknown. Here in the Northeast we wonder about the effects of climate change on cold-adapted montane forests, which may slowly shift uphill and thus offer less habitat to the birds that live in them. Climate change may also result in increased mortality during migration due to increased storms, unseasonal cold snaps, or other perturbations of long-term weather patterns.