Intraspecific competition and winter sociality in white-winged snowfinches (Montifringilla nivalis)

In winter in the mountains, foraging is challenging due to low availability of food, even for species adapted to cold environments. Forming social groups can then improve foraging efficiency but may also increase intraspecific competition. White-winged snowfinches (Montifringilla nivalis) use alpine habitats all year round and forage in groups during the winter season. Studies dealing with the social behaviour of this species or the competitive situation in their foraging groups are lacking. However, knowledge of the social behaviour would help to understand how snowfinches survive winter conditions at high elevations. Here we investigated how snowfinches interact at artificial feeding sites. Specifically, we were interested in how they cope with competition for food within flocks, how individuals differ in their social behaviour and how individual behaviour is linked to morphological characteristics and to getting access to food. We provided supplementary food at two identical food patches that we placed 6-8 meters apart from each other. We used video recordings to monitor how snowfinches distributed between the alternative patches and when agonistic interactions for food resources occurred. Further, we observed colour-ringed snowfinches within groups, to examine how they interact with conspecifics, how close they get to the most profitable positions on the feeding patch, and what beak colour and sex they have. We found that snowfinches in groups of up to 60 individuals preferentially chose the food patch where their group members were feeding instead of the other, unoccupied patch. Moreover, the number of agonistic interactions decreased with increasing group size. The individuals involved in more interactions foraged closer to the centre of the food patch and were mostly males. We also showed that individuals who initiated more agonistic interactions might have blacker beaks than their conspecifics. We suggest that snowfinches benefit more from foraging in groups in winter than they suffer from competition. Nevertheless, it seems that individuals differ in their competitive ability. The more aggressive birds may have better access to food. Their beak colour could act as a signal for aggressiveness or competitiveness in interactions at feeding sites.