Acadian Flycatcher (Empidonax virescens) Nest Tail Structure and Function in Temperate Forests

摘要

Streamers of hanging plant debris (nest tails) are commonly used for nest concealment by tropical Tyrannid flycatchers. Of the 35 species of Tyrannid flycatchers that regularly occur in temperate North America, only the Acadian flycatcher (Empidonax virescens) retains use of nest tails. To better understand the prevalence and possible function of nest tails in temperate breeding Acadian flycatchers, we investigated 145 nests in two habitat types (deciduous and hemlock (Tsuga Canadensis) dominated) in southwestern Pennsylvania in 2006-2007. The primary constituent of nest tails was catkins of oak (Quercus sp.) and American beech (Fagus grandifolia) along with other plant debris entangled in arthropod silk. Debris availability was generally sparse but appeared more common on nest as opposed to randomly selected branches. An index of nest tail "prominence," involving both the length and number of tails, was negatively related to nest height. Variation in nest survival rates was poorly explained by nest tail prominence, and no models evaluated substantially outperformed the null model. Thus, we provide a detailed quantitative description of Acadian flycatcher nest tail characteristics in a northern temperate environment but an understanding of their function in this environment remains elusive.