Background
Blackpoll warblers breed in the boreal forests of North America and winter in South America¹.  Each fall, blackpolls from throughout the North American range migrate eastward to congregate at staging areas along the northeast, including Massachusetts^1,2.  These birds will then fly directly from these locations as far as 3,500 km/2,200 mi over the open ocean to wintering grounds in South America, making stops in the Caribbean islands to rest and feed^2,3.  In total, some individuals will migrate 8,000 km/5,000 mi, making this the longest migration of any North American warbler².  Although these birds are common migrants in Massachusetts, they are at the extreme southern limit of their breeding range in the state⁴.  Currently, blackpoll warblers breed only in the montane spruce-fir forest surrounding the summit of Mount Greylock in the west of the state⁴.

Climate Impacts
Climate change is likely to greatly impact breeding populations within Massachusetts because blackpoll warblers are dependent on limited montane spruce-fir forest habitat for breeding.  This forest type is expected to shift upwards in elevation^5,6.  Some modeling studies have projected breeding populations of blackpoll warblers will be greatly reduced or extirpated from New York, Vermont, and New Hampshire by 2080, depending on the climate scenario used⁷.  This implies complete loss from the state of Massachusetts. 

Although northward shifts in distribution are anticipated⁷, it is unclear how this would impact migration routes.  The species does migrate through locations as far south as Cape Hatteras, North Carolina⁸, so it seems likely that Massachusetts will remain within the migration corridor.  Although changes in the timing of migration have been observed for many short- and medium-distance migrants^9,10, long-distance migrants such as blackpoll warblers do not appear to be changing migration timing¹⁰.  This raises concerns that as phenological (seasonal timing) changes occur for plant and insect species, blackpoll warblers may be exposed to significantly different environments along migration routes than they have in the past¹⁰.