eWestern BirdsThe Quarterly Journal of Western Field Ornithologists
Vol. 38, No. 2
Western Field Ornithologists
Breeding Avifaunal Changes in the San Francisco Bay Area 1927–2005
William G. Bousman
ABSTRACT: I compare the breeding avifauna of the San Francisco Bay area prior to 1927 with the current breeding avifauna. There were 172 breeding species known in the San Francisco Bay area prior to 1927, whereas today there are 215. Four species have been extirpated, whereas 47 are new. Most of the species added to the breeding avifauna are casual, irregular, or accidental, but 17 of these now breed regularly. The reasons for these avifaunal changes are diverse but in many cases are related to range expansions or contractions. Factors contributing to expansions include rebound of populations following cessation of commercial harvesting, conversion of salt marshes to salt-evaporation ponds, maturation of second-growth forests, urban adaptation, exploitation of artificial reservoirs, and habitat protection.