By beak or wing: bird foraging strategies with respect to aggressive behaviors.

Abstract

Whether within or between species, individuals often must compete with each other for food, shelter, and mates. For this reason, aggression might be a common behavior between individuals occupying close niches. Theoretically, the greater the resource overlap between two individuals, the greater the opportunity to see aggressive interactions occur between them. For this reason, within the bird community at UMBS, we expected aggressive intraspecific interactions to happen more frequently than aggressive interspecific interactions, with a lesser occurrence of peaceful coexistence within species while foraging. However, at platform feeders, no significant difference was observed with the distribution of the type of interactions between interspecific and intraspecific interactions of birds while foraging for food (X2=2.23, df=1, 0.2<p<0.4). We further looked into the frequency of aggressive interspecific and intraspecific interactions to see if it followed the community wide trend. We found that aggression did not occur more frequently in any specific bird pair than in the others (X2=12.52, df=7, 0.1<p<0.5). Another question that we addressed was whether a larger bird size would be a determining factor in the outcome of interspecific aggressive interactions. In almost all instances of aggressive behavior, the larger bird won and remained at the feeder while the smaller bird was forced to retreat (X2=25.3, df=1, p<0.001). Again we tested to see if individual species followed the community wide trend in bird size determining the outcome and found statistical evidence to support this. Although in this study we concluded that aggression is no more frequent in intraspecific interactions then interspecific interactions we did find strong evidence to support that size does determine the outcome of aggressive interspecific interactions.