AUTUMN POPULATIONS OF LANDBIRDS ALONG CENTRAL COASTAL CALIFORNIA 1976-1986

The autumn migration of 110 species or distinct races of birds was mon itored from 1976 to 1986 by a standardized mist-netting program on the coast of central California. A peak in migration numbers occurred bet ween mid-August and late October in a given year. Young birds were cap tured 9.1 times more frequently than adults. The number of birds bande d annually in the autumn was not correlated with the number banded in the summer. There was no correlation between the number of young and a dult birds banded in a given year. The 44 most common bird taxa had hi gh annual variation in numbers and young:adult ratios, sometimes by a factor >10. The young:adult ratios were higher for species of woodland habitat, breeders along the coast and interior mountains of Californi a, and much higher for neotropical migrants and permanent residents wi th a winter influx of individuals. Adults of species breeding in Calif ornia mountains varied greatly in annual capture rates. The high annua l variation emphazies that long-term studies are necessary to understa nd the importance of an area to individual or groups of species during migration periods. A higher diversity of species and greater number o f individuals were captured during autumn than summer, and habitat alo ng migratory routes may be as essential as breeding and wintering habi tat.