Distribution, Status, and Origin of Water Pipits Breeding in California

Abstract

We investigated the racial identity, distribution, and abundance of Water Pipits (Anthus spinoletta) breeding in the mountains of California. This common nesting species of alpine tundra was not known to breed in California until the 1970s; a review of historical evidence suggests recent colonization. Mensural and plumage comparisons show California populations to be A. s. alticola, the breeding race of the Rocky Mountains. This is of biogeographical interest, because the abundant wintering and migratory pipit of California is A. s. pacificus, while alticola normally occurs hundreds of miles to the east. Water Pipits currently nest in mesic alpine vegetation throughout much of the southern and central Sierra Nevada. Breeding densities are highest and most uniform in the southernmost part of this range. The only known breeding population in California outside of the Sierra Nevada occurs on San Gorgonio Mountain in southern California. We hypothesize that the previous absence or rarity of breeding Water Pipits in the Sierra Nevada may be attributable to the most recent paleoclimatic xerothermic period, the Hypsithermal (ca. 5,000 to 2,900 years BP), which impoverished many alpine biotas of arctic-old cordilleran affinity. Climate and habitat differences may prevent pacificus from breeding in California, and geographic barriers may have hindered colonization by alticola. The occurrence and timing of the present colonization may be fortuitous. Alternatively, it is possible that prior colonization of Great Basin ranges by alticola facilitated eventual dispersal to the Sierra Nevada.