Unfamiliar stopover sites and the value of social information during migration
The better informed an individual, the better able to meet the demands of a variable environment. When a migratory bird stops over during passage, it must adjust to unfamiliar surroundings, satisfy nutritional demands, compete with other migrants and resident birds for limited resources, avoid predation, balance conflicting demands between predator avoidance and food acquisition, and often cope with unfavorable weather. A successful migration depends on solving these and other problems, the solutions to which are measured in units of time and condition. Migrants that gather reliable information about unfamiliar habitats in a timely fashion increase the likelihood of a successful migration. For example, a migrant may estimate food availability or predator pressure faster and more accurately by combining personal information gathered while sampling with social information obtained while observing the behavior of other migrants. In this paper, we provide a brief review of information use in the context of migratory stopover, a subject that has received little attention, and present preliminary results of an ongoing field investigation of the use of social information by migrants. Focal sampling of free-ranging and radio-tagged Nearctic-Neotropical passerine migrants in coastal habitat following flight across the Gulf of Mexico suggests that migrants respond to a lack of information by foraging in temporary feeding assemblages. This preference for flock foraging declines over the course of the stopover period in insectivorous migrants but persists in omnivorous birds, which suggests that the value of social information depends, in part, on a migrant's foraging ecology. We argue that social foraging enables migrants to assess more fully unfamiliar environments during stopover, thereby reducing risks associated with lack of information.