Status of breeding and wintering Snowy Plovers in San Diego County, California, 1994–1999

Abstract

We conducted intensive surveys of breeding and wintering Snowy Plovers (Charadrius alexandrinus nivosus) in San Diego County from 1994 through the winter of 1999. We found Snowy Plovers using 11 sites within the study area for nesting and at least 18 sites were used during winter months. Estimated breeding populations of Snowy Plovers within San Diego County fluctuated among years, and males always outnumbered females; fewer than 325 Snowy Plovers were present during any breeding season. Two sites consistently supported 65% of nesting pairs during this study, both at military installations. Nesting sites with fewer than five breeding pairs were unlikely to produce fledglings. Nest success over the entire area ranged from 50–58% and reproductive success was on average fewer than 0.5 fledglings produced per adult plover. Approximately 227–367 Snowy Plovers wintered within San Diego County from 1995–1999, which is within the range of winter population estimates from the mid-1980s. Neither breeding nor wintering numbers of plovers in San Diego County have increased since the 1980s, and it is unlikely that populations can increase given the low rates of reproduction. In addition, the concentration of most nesting pairs at a few sites makes this population more vulnerable to local extirpation.