Interim Summary: Nesting Counts of Ospreys and Brown Pelicans in Northwestern Mexico, 2006

Abstract

The distribution and abundance of nesting populations of California brown pelicans (Pelecanus occidentalis californicus) and ospreys (Pandion haliaetus) were documented in 2006 in northwestern Mexico. For ospreys only, the 2006 data were compared to population estimates from two previous surveys (one conducted in 1977 and another conducted in the period 1992-1993). Overall, the total osprey nesting population increased from 1977 to 1992-1993 and then only changed slightly by 2006, but included regions with localized declines, increases, and stable populations. Preliminary population estimates for California brown pelicans suggest a large and apparently healthy breeding population. Problem Statement and Implications California brown pelicans (Pelecanus occidentalis californicus) and osprey (Pandion haliaetus) nesting along the coast of northwestern Mexico, including the Gulf of California, are an important component of Pacific Coast populations. Surveys of the osprey nesting population were conducted in 1977 and 1992-93 by Charles Henny (CJH) and Daniel Anderson (DWA), the same observers for this study, which provides a strong basis for comparisons over 29 years. No complete, range-wide survey of nesting California brown pelicans has been conducted in the past, and the subspecies is currently listed as endangered under the Endangered Species Act. The most recent published information for pelicans in the region is from the mid-1970s. Information about the current nesting population size and distribution are a priority need for a delisting analysis. The overall nesting population of ospreys in northwestern Mexico increased 68% from 810 ± 55 (95% C.I.) pairs in 1977 to 1,362 ± 278 pairs in 1992-93, but the population nesting along the Gulf Coast of Baja California remained stationary (255 versus 236 pairs). This atypical pattern of population recovery warrants additional investigation.