Behavioural Processes 100 (2013) 169–173 Contents lists available at ScienceDirect Behavioural Processes jou rn al h om epa ge: www.elsevier.com/locate/behavproc Sex dependent risk management in face of perceived danger of socially foraging Bee-eaters (Merops apiaster) during migration Reuven Yosef a,∗ , Peter Fehervari b , Nufar Yosef-Sukenik c a International Birding & Research Centre in Eilat, Department of Life Sciences, Ben Gurion University of the Negev, P. O. Box 272, Eilat, Israel b Szent István University, Faculty of Veterinarian Sciences, Department of Biomathematics and Informatics, István st. 2, H-1078 Budapest, Hungary c Department of Education, Tel Aviv University, Ramat Aviv, Israel a r t i c l e i n f o Article history: Received 14 June 2013 Received in revised form 28 September 2013 Accepted 30 September 2013 Keywords: Sex Time minimizer Energy maximizer Bee-eater Body condition Eilat a b s t r a c t The proximal reasons and ultimal consequences of decisions made during foraging by breeding individ- uals 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 1.05 g/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. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Time, energy and personal safety are the three most impor- tant factors known to define migratory strategies and individual decisions in migratory birds (Alerstam and Lindström, 1990). The evolutionary pressure driving these decisions is thought to be dif- ferent in migratory seasons and amongst sexes. In autumn both males and females are prone to optimize for survival, while in spring males optimize for earlier arrival at the breeding grounds (Jakubas and Wojczulanis-Jakubas, 2010; Kovács et al., 2011). The consequences of these selective pressures may realize sex-specific differences in migration strategies, in habitat usage and in foraging strategies during the non-breeding period (Lewis et al., 2002; Catry et al., 2007). The proximal reasons and ultimal consequences of the decisions made during foraging by breeding individuals are widely ∗ Corresponding author. Present address: P. O. Box 272, Eilat 88000, Israel. Tel.: +972 57 7671290; fax: +972 86376922. E-mail addresses: ryosef@eilatcity.co.il (R. Yosef), Fehervari.Peter@aotk.szie.hu (P. Fehervari), nufaryosef@gmail.com (N. Yosef-Sukenik). studied in numerous avian systems (Milner-Gulland et al., 2011). However, the effects of these decisions is more pronounced in the case of birds on migration as they presumably spend more time and energy foraging than on the actual journey itself (Hedenström and Alerstam, 1997). Birds also have to make foraging decisions in foreign environments, concerning exotic diets, while en route. Moreover, large areas have to be covered where foraging is often impossible resulting in long and energy demanding fasting periods (Sapir et al., 2011a). Migrant species often forage in intra and/or interspecific social groups (Alestram, 1990). Presumably, the ephemeral and uneven spatial distribution of foraging patches or stop-over sites, and the high energy demand, drive the aggregation of foraging indi- viduals resulting in foraging flocks of large numbers of birds and species at stop-over sites (Rodewald and Brittingham, 2002). These sites attract a wide variety of predators to a degree that some may even time their breeding to the arrival of the migrat- ing birds (e.g., Falco eleonorae, Falco concolor) (Ferguson-Lees and Christie, 2001). The ecological constraints of social foraging while on migration may however be different compared to the rest of the annual cycle, as individuals have to adjust their behaviour 0376-6357/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.beproc.2013.09.009