Foraging inequalities in large groups: quantifying depletion experienced by individuals in goose flocks

• Published in: Journal of Animal Ecology
• Main Authors: Rowcliffe, J. Marcus, Pettifor, Richard A., Carbone, Chris
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2004
• Subjects: Barnacle goose
• Online Access: http://dx.doi.org/10.1111/j.1365-2656.2004.00783.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1365-2656.2004.00783.x; https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2656.2004.00783.x

Summary Inequalities between individuals represent a major force driving patterns of animal dispersion. Here we use a novel approach to the analysis of feeding competition in large groups, based on photographic sequences of barnacle goose flocks over time. The spatial distributions of individuals derived from these photos were used to describe how individual feeding performance may be affected by patch depletion caused by other members of the flock. This was assessed indirectly by estimating the variation in prior grazing time experienced by individuals. The most successful foragers in a flock (i.e. those experiencing the least prior grazing time) are largely unaffected by depletion arising during the life span of the flock, while the least successful foragers experience very substantial depletion. Furthermore, for the less successful individuals, the average level of depletion increases continuously with both flock size and time spent in the flock. Skew in depletion experienced could not be assessed accurately, although it is likely that there is moderate right skew, i.e. a few individuals do very badly, but more than half do better than the mean. This study suggests that the degree of depletion experienced is related to position within the group, while previous studies of this system have shown that there is strong competition for the better positions. Dominance status is therefore likely to be a strong determinant of feeding performance. Subordinate individuals, being unable to obtain leading positions, may be forced to adopt alternative strategies to improve feeding performance, such as moving more frequently in order to maximize time in smaller or more recently formed groups.