California Brown Pelican <em>Pelecanus occidentalis</em> Community Science Project: Potential for Population Monitoring

From 2016 to 2019, we monitored the distribution, abundance, and age structure of California Brown Pelican Pelecanus occidentalis californicus at nearshore communal roosts along the U.S. West Coast. This effort used “snapshot” surveys during spring and fall, simultaneously engaging up to 111 “community science” participants, i.e., volunteers, on single dates. Volunteers surveyed up to 89 sites and found as many as 22,000 Brown Pelicans. We derived abundance and population structure indices from these data and sought relationships to annual breeding season metrics and large-scale oceanographic indices in the California Current System (CCS). The proportion of immature birds increased during the study period, reflecting improved Brown Pelican productivity in the Southern California Bight after several years of low reproductive output. This increase in productivity coincided with a rise in the abundance of their primary prey, the Northern Anchovy Engraulis mordax. The proportion of immature Brown Pelicans observed in this survey was related to anchovy abundance. Compared to historical records, pelican distribution during fall had shifted north—consistent with climate change predictions—with a hotspot around 37°N. No single environmental driver explained the inter-annual variation in pelican abundance, which was affected by complex ecological dynamics and variable migration of pelicans from the Gulf of California, Mexico. The distribution of pelicans in the CCS suggested a coarse relationship with moderate upwelling and sea surface temperatures, in accord with habitat preferences of the anchovy, although we did not attempt to capture fine-scale predator-prey associations. Our results suggest that resuming the binational community science survey with some protocol improvements will be a valuable, inexpensive, and inclusive way to assess the general status of California Brown Pelicans. Population structure indices are likely to reflect annual variation in prey availability and pelican productivity in the CCS, while changes in total abundance will be more challenging to interpret and will require long-term datasets.