Nonbreeding season ecology and behavior of Eastern Towhees (Pipilo erythropthalmus)

Abstract

Eastern Towhees (Pipilo erythropthalmus) are partial migrants that inhabit dense thickets of shrubs in both breeding and nonbreeding seasons and have declined range-wide by approximately 50% since the mid-1960s. Few studies have addressed the nonbreeding season natural history of Eastern Towhees. The objectives of our study were to (1) describe and quantify nonbreeding habitat use and social interactions, and (2) relate these metrics to winter weather conditions. We captured and radio-tagged 9 Eastern Towhees and tracked them using homing and triangulation for a total of 528 locations from late November 2015 to March 2016, plus 3 Eastern Towhees tracked in 2014–2015. The mean (± SE) home range size (80% kernel isopleth) was 7.31 ± 0.22 ha, and the mean (± SE) core area (30% kernel isopleth) was 1.52 ± 0.94 ha. The mean overlap of home ranges between neighbors was 36%, and 24% between neighboring core areas. The study area was classified into 4 habitats: mowed, blackberry scrub, woody shrub, and wooded. Habitat use did not directly correspond with availability: Eastern Towhees occupied woody shrub habitat most (48% of locations vs. 35% of available habitat), suggesting that of our 4 habitat types, woody shrub was preferred. For weather, wind speed did not significantly affect habitat use, foraging method, vocalizations, or flock size. Although temperature did not significantly affect any of the behaviors, there were trends for less ground foraging and more use of wooded habitat in freezing temperatures. Snow cover influenced habitat use (odds ratio = 0.60), vocalizations (odds ratio = 1.77), and flock size (odds ratio = 1.97), but not foraging. These results contribute to understanding the nonbreeding natural history of Eastern Towhees and demonstrate that inclement weather in the nonbreeding season may influence habitat use and behaviors in ways that could affect nonbreeding season survival.