California gull

In south San Francisco Bay, former salt ponds now managed as wildlife habitat support large populations of breeding waterbirds. In 2006, the South Bay Salt Pond Restoration Project began the process of converting 50% to 90% of these managed pond habitats into tidal marsh. We compared American Avocet (Recurvirostra americana) and Black-necked Stilt (Himantopus mexicanus) abundance in south San Francisco Bay before (2001) and after approximately 1,300 ha of managed ponds were breached to tidal action to begin tidal marsh restoration (2019). Over the 18-year period, American Avocet abundance declined 13.5% (2,765 in 2001 vs. 2,391 in 2019), and Black-necked Stilt abundance declined 30.0% (1,184 in 2001 vs. 828 in 2019). Forster’s Tern (Sterna forsteri) abundance was 2,675 birds in 2019. In 2019, managed ponds accounted for only 25.8% of suitable habitats, yet contained 53.9%, 38.6%, and 65.6% American Avocet, Black-necked Stilt, and Forster’s Tern observations, respectively. Conversely, tidal marsh and tidal mudflats accounted for 42.9% of suitable habitats, yet contained only 18.4%, 10.3%, and 19.8% of American Avocet, Black-necked Stilt, and Forster’s Tern observations, respectively. Using a separate nest-monitoring data set, we found that nest abundance in south San Francisco Bay declined for all three species from 2005–2019. Average annual nest abundance during 2017–2019 declined 53%, 71%, and 36%, for American Avocets, Back-necked Stilts, and Forster’s Terns, respectively, compared to 2005–2007. Loss of island nesting habitat as a result of tidal marsh conversion and an increasing population of predatory California Gulls (Larus californicus) are two potential causes of these declines. All three species established nesting colonies on newly constructed islands within remaining managed ponds; however, these new colonies did not make up for the steep declines observed at other historical nesting sites. For future wetland restoration, retaining more managed ponds that contain islands suitable for nesting may help to limit further declines in breeding waterbird populations.

Hartman, C. A, Ackerman, J. T, Schacter, C. R, Herzog, M. P, Tarjan, L. M, Wang, Y., et al. (2021). Breeding Waterbird Populations Have Declined in South San Francisco Bay: An Assessment Over Two Decades. San Francisco Estuary and Watershed Science, 19(3). http://dx.doi.org/10.15447/sfews.2021v19iss3art4 Retrieved from https://escholarship.org/uc/item/16n259mc

Keywords

birds

Pond Complex

Alviso

Eden Landing

Ravenswood

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San Francisco Estuary and Watershed Science, Volume 19, Issue 3

Mercury contamination and stable isotopes reveal variability in foraging ecology of generalist California gulls

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Mercury contamination and stable isotopes reveal variability in foraging ecology of generalist California gulls admin Wed, 11/22/2017 - 16:21

Document Category

Scientific Reports

Author(s)

Sarah H. Peterson

Joshua T. Ackerman

Collin A. Eagles-Smith

Date

2017

Keywords

California Gull Diet, Movements, and Use of Landfills in San Francisco Bay

admin — Thu, 23 Nov 2017 00:21:53 +0000

California Gull Diet, Movements, and Use of Landfills in San Francisco Bay admin Wed, 11/22/2017 - 16:21

Document Category

Scientific Reports

Author(s)

Joshua T. Ackerman

Dr. Sarah H. Peterson

Date

2017

Keywords

California gull

birds

Forster’s Tern Chick Survival in Response to a Managed Relocation of Predatory California Gulls

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Forster’s Tern Chick Survival in Response to a Managed Relocation of Predatory California Gulls admin Wed, 11/22/2017 - 16:21

Document Category

Scientific Reports

Author(s)

Date

2014

Summary

Gull populations can severely limit the productivity of waterbirds. Relocating gull colonies may reduce their effects on nearby breeding waterbirds, but there are few examples of this management strategy. We examined gull predation and survival of Forster’s tern (Sterna forsteri) chicks before (2010) and after (2011) the managed relocation of the largest California gull (Larus californicus) colony (24,000 adults) in San Francisco Bay, California. Overall, survival of radio-marked Forster’s tern chicks from hatching to fledging was 0.220.03 (meanSE), and daily survival rates increased with age. Gulls were the predominant predator of tern chicks, potentially causing 54% of chick deaths. Prior to the gull colony relocation, 56% of radio-marked and 20% of banded tern chicks from the nearest tern colony were recovered dead in the gull colony, compared to only 15% of radio-marked and 4% of banded chicks recovered dead from all other tern colonies. The managed relocation of the gull colony substantially increased tern chick survival (by 900%) in the nearby (<1 km) colony from 0.040.02 in 2010 to 0.400.12 in 2011 but not at the more distant (>3.8 km) reference tern colony (0.290.10 in 2010 and 0.250.09 in 2011). Among 19 tern nesting islands, fledging success was higher when gull abundance was lower at nearby colonies and when gull colonies were farther from the tern colony. Our results indicate that the managed relocation of gull colonies away from preferred nesting areas of sensitive waterbirds can improve local reproductive success, but this conservation strategy may shift gull predation pressure to other areas or species. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

Keywords

Impact of Salt Ponds Restoration on California Gull Displacement and Predation on Breeding Waterbirds

admin — Thu, 23 Nov 2017 00:21:53 +0000

Impact of Salt Ponds Restoration on California Gull Displacement and Predation on Breeding Waterbirds admin Wed, 11/22/2017 - 16:21

Document Category

Scientific Reports

Author(s)

Caitlin W. Robinson-Nilsen

Date

2013-06-30

Summary

The California Gull (Larus californicus) population in the South San Francisco Bay has increased from fewer to 200 breeding Gulls in 1982, to a peak of 52,172 in 2012. Specific to this study there were 46,030 breeding Gulls in 2010 and 37,716 breeding Gulls in 2011.

Keywords

Impact of Salt Pond Restoration on California Gull Displacement and Predation on Breeding Waterbirds - Annual Report 2010

admin — Thu, 23 Nov 2017 00:21:53 +0000

Impact of Salt Pond Restoration on California Gull Displacement and Predation on Breeding Waterbirds - Annual Report 2010 admin Wed, 11/22/2017 - 16:21

Document Category

Scientific Reports

Author(s)

Joshua T. Ackerman

Jill D. Bluso-Demers

Mark P. Herzog

Caitlin W. Robinson-Nilsen

Garth Herring

Date

2010-12

Summary

Our objectives are to determine the impact of gulls on breeding snowy plovers and Forster’s terns.; Color-mark California gulls at A6 to determine potential nesting distributions after restoration of A6.; Continue our California gull colony surveys to document current population size. Herein, we provide an update of fiscal expenditures and a summary of recent research findings as they pertain to the objectives of this project.

Keywords

California Gull Distribution, Abundance, and Predation on Waterbird Eggs and Chicks in South San Francisco Bay

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California Gull Distribution, Abundance, and Predation on Waterbird Eggs and Chicks in South San Francisco Bay admin Wed, 11/22/2017 - 16:21

Document Category

Scientific Reports

Author(s)

Date

2006-12

Summary

We examined the distribution and abundance of California Gulls throughout the South Bay salt ponds and associated landfills and determined their impact on the reproductive success of American Avocets and Black-necked Stilts.

Keywords

birds

California gull

California Gull Movements in Relation to Nesting Waterbirds and Landfills: Implications for the South Bay Salt Pond Restoration Project

admin — Thu, 23 Nov 2017 00:21:53 +0000

California Gull Movements in Relation to Nesting Waterbirds and Landfills: Implications for the South Bay Salt Pond Restoration Project admin Wed, 11/22/2017 - 16:21

Document Category

Scientific Reports

Author(s)

Joshua T. Ackerman

Collin A. Eagles-Smith

Date

2009

Keywords

birds

California gull