Breeding Habitat:Woodland
Nest Type:Open-cup nesting passerine
Migration Status:Short distance migrant
Nest Location:Ground-low nesting
A widespread occupant of coniferous and mixed woodlands, the status and distribution of Hermit Thrushes has not markedly changed during recent decades. Noticeable expansions or contractions of its breeding range have not been reported, only increases or declines in local populations in response to habitat availability. This information suggests that its populations have remained reasonably stable.
Hermit Thrushes are widely distributed across Canada and the northern United States, and within coniferous forests at higher elevations in the western mountains and northern Appalachians. Along BBS routes, this species is most numerous in southern Canada and the adjacent United States from eastern Manitoba eastward, and locally throughout the western mountains (Relative Abundance Map). These thrushes are also widely distributed in northern Canada and Alaska, populations that are not effectively surveyed by the BBS.
During the entire survey period, the BBS trends are generally positive including significant increases in the Eastern BBS Region, United States, and survey-wide population (Trend List). Increases also occur in 7 states/provinces and 5 physiographic strata, primarily within the Eastern BBS Region. These positive trends generally reflect the trends of Hermit Thrush populations after 1980, when significant increases have occurred in 11 states/provinces, 8 strata, the Eastern BBS Region, United States, Canada, and survey-wide population. In contrast, their trends tend to be more negative during 1966-1979 when there are significant increases in only one strata while declines are evident in 4 states/provinces, one strata, and the United States.
The trend map reflects the increases in the Hermit Thrush populations of eastern North America. These increases are most apparent from the northern Appalachians through New England, and from Minnesota across southern Canada to the Maritime Provinces (Trend Map). In the western mountains, the trends are mixed with scattered increases and declines, reflecting the generally non-significant trend estimates in this region.
Hermit Thrushes are short-distance migrants, with the majority of their populations wintering in the southern United States. As is true for most short-distance migrants, these thrushes may be subjected to unusually high mortality during winters with severe weather. For example, Robbins et al. (1986) reported declines in their populations in eastern North America following the winters of 1976-1978. The declines during these winters are somewhat apparent in the survey-wide indices, although declines of similar magnitudes have occurred during other years (Survey-wide Annual Indices). Within states/provinces and physiographic strata, Hermit Thrush populations exhibit a variety of temporal patterns in trends. In eastern North America, the Maine population declines through the mid-1980s, followed by an increase (Maine Annual Indices). The New York population has been slowly increasing, while the opposite trends have occurred in Vermont (New York Annual Indices). (Vermont Annual Indices). Declines during 1976-1978 are evident in the indices from Maine and Vermont, but not in New York. They also occur in the indices from the Northern New England and Northern Spruce-Hardwoods strata (Northern New England Annual Indices). (N. Spruce-Hardwoods Annual Indices). However, similar short-term declines occur during other years, especially in the mid-1980s. Whether these declines are the result of excessive mortality during winter, or other factors is unknown.
In western North America, the Hermit Thrush populations tend to exhibit considerable annual fluctuations in abundance, with noticeable increases and declines occurring at regular intervals. Examples include the Central Rockies and Dissected Rockies strata (Central Rockies Annual Indices). (Dissected Rockies Annual Indices). In California, populations increased between the late 1970s and mid-1980s, followed by a slight decline (California Annual Indices). Increases are also evident in the Pitt-Klamath Plateau stratum (Pitt-Klamath Plateau Annual Indices). However, populations in most states/provinces vary considerably from year to year with little consistency in their trends (Colorado Annual Indices). (Oregon Annual Indices). This variability suggests that these western populations are fluctuating in response to local conditions that are not uniformly present across the region.
Robbins, C.S., D. Bystrak, and P.H. Geissler. 1986. The breeding
bird survey: its first fifteen years 1965-1979. U.S. Fish and
Wildl. Serv. Res. Publ. No. 157. 196 pp.