Date of this Version
The Prairie Naturalist 52:45-57; 2020
Average winter temperatures in the north-central United States have been increasing since the 1970s, and this warming might influence winter distributions of birds in the region. Species potentially influenced by such winter warming include short-distance migrants for which the northern boundary of the winter range is influenced by temperature, such as hermit thrush (Catharus guttatus), yellow-rumped warbler (Setophaga coronata), and fox sparrow (Passerella iliaca). We examined winter records during 1974–2017 from a citizen-science bird observation database for South Dakota to determine recent trends in winter records for these three species. We compared their occurrence patterns with those for three benchmark species (i.e., American black duck [Anas rubripes], Townsend’s solitaire [Myadestes townsendi], and varied thrush [Ixoreus naevius]), for which winter records are not expected to respond to warming winters in South Dakota. All three study species showed marked recent increases in the number of winter records in South Dakota. Logistic regression with model selection identified year as an important predictor of occurrence for all three study species, with higher probabilities of occurrence in recent years. This contrasted with winter occurrence patterns for benchmark species, for which year was positively associated with winter occurrence only for Townsend’s solitaire. Early winter temperatures were included in competitive models for hermit thrush and yellow-rumped warbler, with increased probabilities of occurrence in years with higher temperatures. For benchmark species, only winter occurrence of American black duck was positively associated with early winter temperatures. These data suggest that all three study species are expanding their ranges northward in the north-central United States during a period of winter warming, but other factors in addition to winter temperature are also influencing this trend.