Dynamics of the winter distribution of rosy finches, Leucosticte arctoa, in Montana.

Abstract

During the winter of 1977-1978 rosy finches were reported across the eastern prairies of Montana, whereas in 1978-79 they were limited to grasslands adjacent to the western mountains. Winter snowfall and days of snow cover on the prairies were similar during both winters. January-July precipitation in 1977 was 23% below normal, whereas it was 50% above normal in 1978. Variability in the winter distribution appeared to be a function of early spring and summer precipitation on the prairies (more rain produced more seeds and taller plants) and snow depth relative to plant height (which affected food availability). When food was scarce the finches moved farther onto the prairies.-Authors