Playbacks of mobbing calls of Black-capped Chickadees as a method to estimate reproductive activity of forest birds

Community-level indices of reproductive success are useful for measuring or monitoring demographic effects of habitat alteration on birds. We present a time-efficient method to estimate the relative reproductive activity of t he forest songbird community. A recording of mobbing calls of Black-capped Chickadees (Poecile atricapillus) was broadcast at preselected stations dur ing the breeding season. These calls attracted individuals of many bird spe cies present in the vicinity, allowing visual detection of reproductive act ivity (e.g., adults carrying food or presumed pairs). In mature deciduous f orests of northern New Brunswick, 50 bird species responded to the playback s. playbacks significantly increased the probability of visual observations of birds compared to silent observations conducted before broadcasting mob bing calls. In coniferous forests of central Quebec, playbacks attracted 24 species and also provided a significantly greater opportunity to make visu al observations of individual birds. In New Brunswick, mobbing playbacks fa cilitated more observations of reproductive evidence relative to point coun ts. Observation periods were brief and a 306-ha plot (1.75 x 1.75 km, 64 po ints spaced 250 m apart) could he surveyed by foot in less than 32 observer -hours. The proportion of individuals of a given species showing evidence o f reproductive activity was used as an index of reproductive success. Black -throated Blue Warblers (Dendroica caerulescens) and Ovenbirds (Seiurus aur ocapillus) had a reproductive index consistent with their true nesting succ ess as derived from intensive nest monitoring on the same plots.