Brown Pelicans, Pelecanus occidentalis californicus (Aves: Pelecanidae): Five decades with ENSO, dynamic nesting, and contemporary breeding status in the Gulf of California

Abstract

The California Brown Pelican subspecies (Pelecanus occidentalis californicus) was removed from the US endangered species list in 2009, along with the entire species of Brown Pelican throughout North America. The Gulf of California subpopulation within the entire metapopulation (= subspecies) comprises the majority of nesting (~76% of P. o. californicus). The US classifications were based on pollution effects in the Southern California Bight (SCB) during the early 1970s; official listing-recognition in Mexico (NOM-059-SEMARNAT-2010) occurred in 2010 and it continues. Unfortunately, Brown Pelican conservation across the US/Mexico border has been largely uncoordinated. Recent declines in the SCB subpopulation are not well-documented, whereas representative subpopulations in the Gulf of California have received continual study since the US listing. Until the early 2000s, Gulf pelican breeding populations changed little. El Niño/Southern Oscillation continues to be a major factor driving annual pelican breeding intensity and success, with a slightly weaker effect to the north. Nest attempts (NA) in the southern Midriff zone and to the south of our monitoring zone have declined in the last decade, in especially extreme and unprecedented ways in a period of unusual warming in the last 3 years (2014–2016), termed by some as the “Blob”. Other factors (such as human disturbance and commercial fishing) have likely exacerbated recent warming effects in some areas. Recent data also suggest the pelican is in a process of minor range-shifting toward the northern Gulf, and there are no definitive indications of a recent NA decline in that zone. Monitoring over the entire range, past 2016, will be important to determine whether populations have begun a long-term decline or will recover to normal baseline levels. The health of pelican populations is an important indicator of overall ecological health in the Pacific region and not an isolated phenomenon.