Differences in aggressive responses do not contribute to shifts in a sapsucker hybrid zone

Abstract

ABSTRACT Interspecific interactions, such as aggressive territorial behaviors, can be important in establishing range boundaries, especially in hybrid zones where 2 divergent taxa meet and interbreed. Further, differences in the aggressive responses among hybridizing taxa can be important in moving hybrid zones, especially when there are strong asymmetries in their aggressive interactions. To determine how between-taxon interactions may be contributing to hybrid zone movement between 2 species of sapsucker, we studied an aspect of territory maintenance: aggression toward a territory intruder between species. Using a series of field experiments involving playback and taxidermic mounts, we tested whether Red-naped (Sphyrapicus nuchalis) and Red-breasted (S. ruber) sapsucker differ in their levels of aggressive behavior, thereby influencing the dynamic nature of the hybrid zone between these species. We found that 2 of the 3 aggressive response variables we measured differed between the 2 species. Red-naped ...