Is Territory Switching Adaptive? Effects of Predation on Within-Season Nesting Dispersal in Barn Swallows, Hirundo rustica erythrogaster - Kyle Donahue - 2015

Abstract

Many animals are territorial during the breeding season. The defense of a particular territory is often dynamic, leading to a pattern of territory switching during, or between, successive breeding attempts. Territory establishment and defense are viewed as costly behaviors, and questions remain about the potential factors leading to, as well as the benefits of, territory switching. One factor influencing such movement is the avoidance of predation. Avian species with multiple clutches provide a good system to study how predation influences territorial movements within a breeding season. I observed a color-banded population of barn swallows (Hirundo rustica erythrogaster) in Boulder County, Colorado and quantified predation events, the number of fledglings from each nest, and the distance between the first and second nests. I was specifically interested in how predation influences within-season movement in the barn swallow. I found that predation does not influence the frequency of moves to different nests for a second clutch. However, I did find that as the distance between the first and second nest increased, reproductive success of the second clutch decreased. I also found that predation does not influence whether birds move within or outside of their estimated territories. Finally, I found no difference in reproductive success depending on the decision to move or to stay for a second clutch. These results suggest that predation has little to no effect on barn swallow decisions to move to a different nest for a second clutch. Thus, pairs may be able to assess high-risk predation zones and select nest sites accordingly, reducing their need to disperse to more distant nests for a second clutch. Other factors, such as the ubiquity of the northern fowl mite (Ornithonyssus sylviarum, a common nest parasite), and individual variation in territory size, may give further insight into the inherently widespread trend of movement between nests in Colorado barn swallows.