Although many avian species in western North America have suffered recent population declines, a few have increased over the same period of time (Jehl and Johnson 1994). Many of the increases, such as parrots’ (Psittacidae), can be attributed strictly to anthropogenic influences (Johnston and Garrett 1994). Among those species showing apparent natural population increases in California is the Black Skimmer (Rynchops niger), which first occurred in the state in 1962 (Small 1963, 1994) and is now a resident breeder with a population in 1995 of about 1200 pairs. Recent studies in this region have documented its nocturnal activity pattern in the breeding season (Wilson 1995) and winter (Gazzaniga 1995, de la Cueva and Fernández 1996), food habits (Wilson 1995), and pattern of chick growth (Schew and Collins 1990, 1991). In this paper we review the status of the Black Skimmer in California with emphasis on the size and location of breeding colonies and overwintering aggregations (Figure 1). We also include a list of museum specimens of Black Skimmers taken in California (Appendix).