Occurrence, morphometrics, and plumage variability among Leach’s Storm-Petrels Oceanodroma leucorhoa in the California Channel Islands, 1976–2015

Abstract

We mist-netted and examined Leach’s Storm-Petrels Oceanodroma leucorhoa (LESP) caught during 1991–2015 at three locations in the California Channel Islands (CCI): Prince Island, Santa Barbara-Sutil islands and Scorpion Rock. Although mist-netting methods and effort varied between two study periods (1991–1995, 2004–2007 and 2015), during 750 h effort we captured 41 LESP during April–August, with two of these recaptured after initial banding. The majority (78%) were classified as likely breeders based on a well-developed incubation patch. We summarize island-specific efforts, capture rates and morphological measurements made at these three CCI locations. Captured LESP displayed a multimodal distribution in the overall degree of white rump plumage, with 28% classified as mostly “dark-rumped.” The majority of LESP (72%) captured in the CCI have variable white rumps, similar to what has been reported for northern California and the Farallon Islands. However, the relative proportions of “dark-rumped” individuals captured in the northern CCI is intermediate, within the shift starting at the Farallon Islands and increasing in prevalence toward the San Benito Islands, Baja California. More remains to be learned about LESP in the CCI, for which additional mist-netting efforts are needed, using a standardized approach that targets LESP.