Widlife Relations — Abstract of Paper


Factors Affecting the Abundance and Distribution of European Starlings at the San Joaquin Experimental Range
Kathryn L. Purcell,¹ Jared Verner,¹ and Sylvia R. Mori²


We examined population trends and factors related to the abundance and presence of European starlings (Sturnus vulgaris) at the San Joaquin Experimental Range in the foothills of the western Sierra Nevada, 31 km east of Madera, California. Starlings first appeared there in low numbers in the late 1960s and are now abundant breeders. Simple models examining trends in starling numbers and presence/absence using point-counting data from 210 counting stations from 1985 through 2000 showed significantly increasing yearly trends in starling abundance and distribution. The yearly trend in abundance, however, became nonsignificant when weather patterns were included. Similarly, starling presence/absence showed an increasing trend over years, but the trend became sinusoidal when weather and habitat variables were included. Our data show that spurious results may occur when appropriate explanatory variables are not included in the analysis of population trends. Starlings were more abundant after years with cool summers, warm, wet winters, and on early and late count dates. Starling presence was related to habitat attributes generally considered necessary for foraging—level, open woodlands with fairly well-developed, accessible soil. Summer is the time of year when resources are most limiting for starlings in the foothill oak woodlands, as they primarily forage on arthropods in moist soils. Cool summers and wet winters permit the soils, especially swales, to remain moist and productive longer, thereby promoting higher starling abundance. Research is needed on the potential effects of starlings on native species of birds and the conservation and production values of the ecosystems they have invaded.