Ground-based autumn migration of Blackpoll Warblers at Harrison Point, Barbados

The multi-authored hypothesis postulates that during autumn migration in the West Indies, Blackpoll Warblers (Dendroica striata) have sufficient energy reserves to fly overhead without stopping, and that grounding of these warblers is sporadic. We monitored migration with mist nets at Harrison Point (HP), St. Lucy, Barbados (13degrees19' N, 59degrees39' W) from 29 September to 9 November 1997 (42 d). We also used sight observation data from HP in autumn from 1993 to 2000 (62 d, excluding 1997) to complement the results obtained from mist-net captures. Blackpoll Warblers arrived throughout the day, but although HP concentrates migrants, blackpolls were generally infrequent (less than daily occurrence) and uncommon (mean of <3 birds/day, excluding occasional "fallouts"). The arrival of grounded Blackpoll Warblers in 1997 was significantly associated with low barometric air pressure. The mean mass (adjusted for body size) and fat class of "fallout" birds captured during a storm were significantly greater than for non-"fallout" birds. The mean fat load of "fallout" birds was sufficient for them to have reached their winter destination,in South America without refueling in Barbados, but most other Blackpoll Warblers with lower mass lacked sufficient fat to complete their over-water migration. Our results generally support the multi-authored hypothesis, and thus the prevailing view that Blackpoll Warblers undertake a long transoceanic migration during autumn (primarily in October) over the western North Atlantic Ocean to South America.