Blackpoll Warbler migration is among the most amazing of any species in the world. Blackpolls winter in South America and return northward through the Caribbean in late April and May, with Texas at the western fringe of their northward passage. One of the latest spring migrant warblers in the Northeast, they are regularly seen on passage into early June. They breed across the boreal forest from Newfoundland to Alaska and south to New York and Minnesota. In fall, the species angles much more toward the southeast, and the bulk of the population flows through Atlantic Canada and New England. These small birds fatten up in September, sometimes doubling their mass, and from this launching point they strike out over the open ocean, with their next landfall two or three days later in the eastern Caribbean or even mainland South America.
The easterly shift in this species’ migration is readily apparent in the animation above. Note how scarce the bird is south of Cape Hatteras in fall. Although common in spring, it is very rare in the Southeast and along the Gulf Coast in fall.
A few oddly located hotspots appear in west Texas and eastern Colorado in spring, which may be driven in part by a disproportionate tendency for birders to visit “migrant traps” in May in those regions. With more random counts in the grasslands and prairies (rather than the few isolated woodlots), the occurrence in those areas would likely drop significantly, relative to the main migration areas. As always, remember that these models are working with eBird data, and there are biases in how birders sample the landscape. For this reason, we have tried to promote the use of random counts so that the widespread habitats (with less rare bird potential) are sampled in a proportion that more closely resembles their percentage “on the ground”.