Changes in Evermann's Rock Ptarmigan Density on an Eastern Portion of Attu Island, Alaska, 2003–2009

Investigations of insular populations of Rock Ptarmigan (Lagopus muta) in Alaska over time are uncommon. We documented changes in spring density of Evermann's Rock Ptarmigan (L. m. evermanni) on a portion of Attu Island, Alaska, from 2003 through 2009. Populations were 8.5 birds/km2 in 2003, decreased by approximately one-half in 2004 (3.8 birds/km2), and continued to decrease in 2005 (1.9 birds/km2), 2006 (0.8 birds/km2), and 2007 (0.6 birds/km2), reaching a low of 0.3 birds/km2 in 2009. The overall decrease from 2003 through 2007, and 2009 was approximately 97%. We conclude the most reasonable explanation for the decline was poor recruitment (90% decrease from 2003 to 2006) of young (subadult = yearling) to the spring population, possibly related to natural cycling of the population. We could not identify specific factors to explain the low recruitment.