Sex dependent risk management in face of perceived danger of socially foraging Bee-eaters (Merops apiaster) during migration

Abstract

The proximal reasons and ultimal consequences of decisions made during foraging by breeding individuals are widely studied in numerous avian systems. However, the effects of these decisions are more pronounced in migratory birds because they spend more time and energy foraging than on the actual journey itself. The peak flowering and pollination period of crops in southern Israel, when large numbers of hives are transported to the region, coincide with the peak migration of Bee-eaters. We hypothesized that Bee-eaters cue on conspecifics while foraging at a stopover site, react to perceived danger at a given foraging patch, and that the degree of risk taken by an individual was a function of body condition and sex. Bee-eaters were caught on 44 different mornings in spring 2004, 2005, and 2009. A sex-dependent trapping was noted and significantly more females were caught in the first bout. The sex ratio remained significantly male biased in bouts 3-8. Birds caught in the first bout were heavier in comparison to those caught in the second bout, and there was a significant interaction between sex and bouts. From the second bout onwards both sexes showed a significant increase in body mass, by 1.05g/bout on average (±0.6 SD), however wing lengths remained similar for both sexes. We conclude that migrant Bee-eaters cue on conspecifics to evaluate predation risks when socially foraging at a localized food patch and males, who we assume to be time-minimizers, are more likely to forage at a novel site and once danger of foraging is perceived only high energy demand individuals will attempt to hunt.

Keywords: Bee-eater; Body condition; Eilat; Energy maximizer; Sex; Time minimizer.