Pattern of Movement By Summer Tanagers (Piranga Rubra) During Migratory Stopover: a Telemetry Study

Abstract

AbstractHow well migratory birds meet en route contingencies depends on their ability to locate resources and avoid sources of stress in an unfamiliar setting. Exploration is a means by which migrants could collect information about the kinds, distribution and abundance of available resources and places safe from predators. We used radio-telemetry to study the movements of 24 summer tanagers (Piranga rubra) during stopover on a barrier island following migration across the Gulf of Mexico. The movement of some individuals was characterized by high linearity and low turn bias (i.e. alternating left and right turns). The combination of left- and right-hand turns while maintaining an overall linear track represents an efficient way of exploring an unfamiliar area. Other summer tanagers restricted their movements to a particular area (e.g. low directionality and high meander ratio), which may reflect less time spent in exploration. Birds that had been on the island for a day and a night displayed a pattern of movement less consistent with exploration than did 'newly arrived' birds. Given pressure to minimize migration time, the time a migrant spends in exploration probably depends on the cost of acquiring information and the benefits to be gained, the ratio of which surely varies among individuals.