Ij. Lovette et Rt. Holmes, FORAGING BEHAVIOR OF AMERICAN REDSTARTS IN BREEDING AND WINTERING HABITATS - IMPLICATIONS FOR RELATIVE FOOD AVAILABILITY, The Condor, 97(3), 1995, pp. 782-791
We investigated food availability for a long-distance migrant species,
the American Redstart (Setophaga ruticilla), in both its summer breed
ing habitat in New Hampshire and in its winter habitat in Jamaica. We
used four components of foraging behavior (prey attack rate, foraging
speed, time spent foraging, and foraging maneuver use) as indicators o
f the relative availability of prey in the two seasons. Redstarts atta
cked prey at a significantly greater rate in summer than in winter, in
dicating that foraging birds encountered prey more frequently in summe
r. The winter prey-encounter rate was low even though redstarts moved
almost twice as fast while foraging in winter as in summer. Male redst
arts also spent more time foraging in winter (85%) than in summer (43-
65%), possibly to balance the low rate at which they encountered prey.
In winter, redstarts used more foraging maneuvers that were directed
towards small flying prey, whereas in summer they used maneuvers that
resulted in the capture of relatively large and presumably energy-rich
prey such as lepidopteran larvae. That wintering redstarts foraged fa
ster, attacked prey less often, and spent more time foraging than thos
e in summer indicates that the winter is a period of relative food sca
rcity for this species, whereas the breeding season is a period of gre
ater resource abundance.