Abstract
The thaw came very late to Jackson Hole in 2011, with snow melt-out on May 15th. This year shares with 2008 and 2010 the claim of the latest spring over recent decades. The spring snow melt-out is a function of both accumulated snowfall and spring temperatures. A second measure of the advent of spring is the accumulation of growing degree-days (GDD); GDD finally exceeded 225 (°F; 125 °C) on June 23rd, that value being a predictor of 90% leaf-out in aspens. As is usual in late years, overall species richness and total bird density were generally lower across most park habitats. In particular, the foliage insectivores of the deciduous habitats, such as warblers and vireos in willows, aspens and cottonwoods, were much reduced in density (by as much as 50%). Sagebrush habitats, where snow persists longer in late springs and where most species feed on the ground early in the breeding season, were the most impoverished. In two such monitoring sites, #4 (Jackson Lake Junction Grass-sage) and #6 (Airport Sage), there were 1/4 to 1/3 fewer species present respectively, and bird densities were reduced to 43% and 39% of long-term averages for the sites.