ADVANTAGES OF CLUSTERED NESTING FOR LEAST FLYCATCHERS IN NORTH-CENTRAL MINNESOTA

Abstract

Abstract Least Flycatchers (Empidonax minimus) often aggregate their territories, even though advantages of clustering are not apparent. In north-central Minnesota we investigated four potential reasons for clustered nesting in Least Flycatchers: (1) predator deterrence, (2) preferred habitat features, (3) greater food availability, and (4) competitive exclusion. In 1995 and 1996 we compared arthropod abundance, forest structure, and plant species composition inside and outside nine Least Flycatcher clusters. We also compared the response of forest birds to the presentation of a predator (Broad-winged Hawk [Buteo platypterus]), and used point counts to detect any exclusion of potential predators or competitors from the clusters. The predator deterrence hypothesis received the strongest support. In response to hawk presentations inside the clusters, 2.8 times more birds (all species combined) gave 5.8 times more alarm calls than outside, with differences due entirely to the presence of Least Flycatchers. I...