Irruptive Migration of Chestnut-Backed Chickadees to Southwestern Idaho

i document irruptive movements of the Chestnut-backed Chickadee to lucky Peak in southwestern idaho, over 80 km from its regular range. Chestnutbacked Chickadees were captured and/or observed at lucky Peak in 2000, 2004, and 2008. To evaluate the context for this phenomenon, i also examined data on capture of all chickadees and other irruptive species at lucky Peak and numbers of irruptive species recorded on idaho Christmas Bird Counts (CBC) from 1997 to 2011. Though CBCs in the winter of 2004–05 (following the largest movement of Chestnut-backed Chickadees at lucky Peak in fall 2004) found high numbers of many irruptive species, relatively low numbers of Chestnut-backed Chickadees were detected on idaho CBCs that winter. Overall, i observed little correspondence between capture totals at lucky Peak and idaho CBC data for potentially irruptive species in general, and little correspondence between years with Chestnut-backed Chickadees and patterns of any irruptive species in CBC data for the the subsequent winter. The seasonal movement patterns of this species, their regularity, and their causes warrant greater attention. several North american chickadees including the Black-capped (Poecile atricapillus), Boreal (P. hudsonicus), and Mountain (P. gambeli) engage in some level of regular and/or irruptive migration (Ficken et al. 1996, McCallum et al. 1999, Foote et al. 2010), a trait also shared by numerous Old World relatives (van Balen and Hage 1989, Heldbjerg and Karlsson 1997). The Chestnut-backed Chickadee (P. rufescens) is a permanent resident of western North america, primarily in the states/provinces adjacent to the Pacific Ocean (from alaska to California), but it also occurs in the interior, including southeastern British Columbia, northern idaho, and western Montana (Dahlsten et al. 2002). it makes short-distance, especially elevational, movements within or close to its regular range in British Columbia, Montana, and Oregon, and irregular post-breeding dispersal has been documented to northern British Columbia, southwestern alberta, and southern California (Grinnell and Miller 1944, Dahlsten et al. 2002, D. Casey and P. Hendricks, pers. comm.). longer-distance movements are undocumented. Here i provide evidence for rare but regular movements in idaho to at least 80 km (mostly well over 150 km) from the nearest point where the species is resident.