LAUSR

Group hunting where two or more individuals chase the same prey occurs in various vertebrate clades. Its evolution has typically been attributed to the resulting increased prey capture rate. Indeed, many studies have documented positive correlations between the number of individuals and probability of success, suggesting that joint hunting is cooperative. However, all existing data on vertebrates are based on field observations and hence cannot control for factors that may also influence hunting success, such as variation in habitat structure, hunting motivation or prey state. Therefore, we conducted controlled laboratory experiments to test whether hunting performance is affected by group size in the group-hunting yellow saddle goatfish. We presented invertebrate prey in an artificial coral reef and measured hunting performance as a function of manipulated group size, ranging from one to four individuals. We found that individuals hunting alone failed to catch the prey within the trial time limit significantly more often than groups did. Furthermore, we found that time until capture depended on group size, with singletons being slowest and groups of four fastest. With few exceptions, group members were approximately equally likely to catch prey. Hunting success as a singleton did not predict an individual's prey capture probability when in a group, suggesting that group hunting involves some producer–scrounger dynamics. In conclusion, while the experiment cannot address the question of how group size affects individual net calorie intake, the results show that groups are more successful at hunting than singletons are.