There are over 10,000 species of birds living in the world today; all of which play vital ecological services such as seed dispersal or pollination. Birds are territorial species and their aggression can be expressed through acts of dominance at bird feeders. Previous studies have reported a relationship between resource availability and aggression in animals, with aggression increasing with decreased resources. Additionally, it has been reported that higher population densities lead to increased competition for resources; with increased competition we might expect an increase in aggression. The aim of this study was to determine the affects of limited resource availability on feeder aggression in birds. We hypothesize that aggression will increase as resources become more limited. We also predicted that aggression will positively correlate with competitor density. To test our hypothesis and prediction, we performed twenty 2-hour observation periods (all between 15:00pm and 20:00pm) at a bird feeder over the course of two months. There were ten replicates where resources were limited and another ten where resources were unlimited.
Results/Conclusions
More aggressive acts/behaviors were observed during resource limited replicates (4.33 +/- 1.04) compared with resource unlimited trials (2.25 +/- 1.64; P=0.03). Aggression and competitor density were also positively correlated (P=0.01). Of the species observed, the common grackle was the most dominant followed by the brown-headed cowbird. Further research is necessary to evaluate why these two specific species were the most aggressive. Anthropogenic activities have led to population declines in both plants and insects causing a need for research that evaluates how resource limitations affect organisms that rely on insect or plant food sources. This study provides implications on bird behavior in favorable and unfavorable resource conditions for birds.