Cryptic competition from neighbours significantly reduces intake rate of foraging greater white-fronted geese

Abstract

The idea that animals gain a higher food intake rate when foraging in larger groups has been reported in many studies. However, some studies suggested that the number of neighbours under surveillance may play a more important role in affecting food intake rate than flock size. In addition, the effect of the number of neighbours should also depend on the position of an individual within a flock. To test these hypotheses, we examined the effects of flock size, number of neighbours and position within a flock on foraging time, foraging efficiency and intake rate of wintering greater white-fronted geese, Anser albifrons. We observed the foraging behaviours of 490 individual geese from 71 flocks during December 2016–March 2017 at Shengjin Lake, Anhui, China. We found that mean foraging time, foraging efficiency and intake rate were not influenced by flock size, whereas, at the individual scale these variables were significantly affected by the number of neighbours and position within a flock. Moreover, the effect of the number of neighbours on the foraging parameters did not differ between central and peripheral individuals, despite central individuals always having greater foraging time, foraging efficiency and intake rate regardless of the number of neighbours. Both the decreased foraging time and decreased foraging efficiency indicated a potential increase in cryptic competition from neighbours. More neighbours contributed to a decreased intake rate. Our study highlights the possible effects of cryptic competition among neighbours on their foraging behaviour. We hypothesize that an increase in intraspecific competition between neighbours in areas of shrinking wetland habitats may contribute to population declines of wintering geese and other wildfowl.