California Gull population growth and ecological impacts in the San Francisco Bay estuary, 1980–2016

Abstract

The breeding population of California Gulls (Larus californicus) in the San Francisco Bay estuary increased from 24 individuals in 1980 to a peak of over 53,000 in 2014, then declined to 38,040 in 2016. The expansion of the breeding population may be related to the availability of suitable nesting sites in close proximity to anthropogenic food subsidies at landfills. Telemetry data indicate that California Gull movements are largely dictated by the two primary landfills in South San Francisco Bay. The large population of California Gulls has had negative effects on locally breeding shorebirds and terns, especially the Forster’s Tern (Sterna forsteri), American Avocet (Recurvirostra americana), and Western Snowy Plover (Charadrius nivosus nivosus). In South San Francisco Bay, California Gulls were responsible for 13% and 38% of egg predation events at nests of American Avocets and Snowy Plovers, respectively, and 55% and 54% of chick predation events of American Avocets and Forster’s Terns, respectively. The forced relocation of the largest gull colony (~24,000) at Pond A6 in 2010 resulted in increased survival of Forster’s Tern chicks at the adjacent colony at Pond A7 in 2011. The California Gull population and its effects on locally breeding shorebirds and terns are among the most pressing concerns for wetland managers within the San Francisco Bay estuary, especially for the South Bay Salt Pond Restoration Project. Further research is needed to evaluate the gull’s reproductive rates, habitat use, and annual movements and so to clarify its demographics and to quantify its effects on other breeding birds.

California Gull (Larus californicus) Space Use and Timing of Movements in Relation to Landfills and Breeding Colonies

“…Together, these three colonies made up 99% and 97% of all the breeding California Gulls in San Francisco Bay during 2007 (nearly 37,000 individuals) and 2008 (nearly 47,000 individuals), respectively (Burns et al 2018). During 2007 and 2008, approximately 60% of California Gulls bred at Alviso, 10% at Coyote Hills, 12% at Mowry 4/5, and 18% at Mowry 1/2 (Burns et al 2018). The habitats at the breeding colonies were sparsely vegetated levees within former salt evaporation ponds (Coyote Hills and Mowry) or the dry bed of a former salt pond (Alviso).…”

“…The California Gull (L. californicus) breeding population in the San Francisco Bay, California, USA, has increased from 24 individuals in 1980 to over 53,000 in 2014 (Strong et al 2004;Burns et al 2018). The San Francisco Bay contains one of the largest California Gull breeding populations in the world (Winkler 1996;Burns et al 2018).…”

“…The California Gull (L. californicus) breeding population in the San Francisco Bay, California, USA, has increased from 24 individuals in 1980 to over 53,000 in 2014 (Strong et al 2004;Burns et al 2018). The San Francisco Bay contains one of the largest California Gull breeding populations in the world (Winkler 1996;Burns et al 2018). California Gulls could be limiting productivity of several other waterbird species breeding within the estuary (Herring et al 2011;Ackerman et al 2014aAckerman et al , 2014bTakekawa et al 2015).…”

“…California Gulls could be limiting productivity of several other waterbird species breeding within the estuary (Herring et al 2011;Ackerman et al 2014aAckerman et al , 2014bTakekawa et al 2015). Because the San Francisco Bay is highly urbanized and California Gull colonies breed in close proximity to several large landfills, anthropogenic food resources derived from landfills may have subsidized the California Gull population's rapid growth and heavily influenced its use of the landscape (Burns et al 2018).…”

Recent trends in population size and distribution of Ring-billed and California gulls in the western United States

“…Overall, the Ring-billed Gull is more widespread, breeding across the northern United States and southern Canada (Pollet et al 2012), whereas the California Gull is restricted mainly to the Columbia and Klamath river basins, Intermountain West, and northern prairies of the western United States and southern Canada (Winkler 1996). Both species also breed in limited areas on the Pacific coast, but there the only substantial population of either species is of the California Gull in San Francisco Bay (Strong et al 2004, Burns et al 2018.…”