Forster’s tern

The South Bay Salt Pond Restoration Project aims to restore many former salt production ponds, now managed for wildlife and water quality, to tidal marsh. However, because managed ponds support large densities of breeding waterbirds, reduction of pond habitat may influence breeding waterbird distribution and abundance. We investigated habitat use associated with breeding, feeding, and roosting behaviors during the breeding season for American Avocets (Recurvirostra americana), Black-necked Stilts (Himantopus mexicanus), Forster’s Terns (Sterna forsteri), and Caspian Terns (Hydroprogne caspia) in south San Francisco Bay in 2019 after substantial tidal marsh restoration, and compared results to a 2001 survey (before restoration). In 2019, managed ponds (26% of currently available habitat) were selected by waterbirds engaged in breeding behaviors (> 39% of observations), foraging (> 42%), and roosting (> 73%). Waterbirds avoided tidal habitats (43% of available habitat), comprising < 17% of observations of breeding behavior, < 28% of foraging observations, and < 13% of roosting observations. Waterbird densities increased in managed ponds between 2001 and 2019, and decreased in active salt ponds, especially among feeding Avocets (92% decrease) and Stilts (100% decrease). Islands were important for waterbirds observed breeding and roosting (45% of Avocet and 53% of Tern observations). Avocets and Stilts fed primarily on wet bare ground (65% and 58%, respectively), whereas feeding Forster’s Terns and Caspian Terns used mostly open water (82% and 93%, respectively). Within ponds, Avocets were associated with islands (131 m closer than expected). Stilts and Forster’s Terns were also associated with islands (68 m and 161 m closer than expected), except when feeding (1 m closer and 90 m farther than expected). Avocets and Stilts were associated with pond levees (39 m and 41 m closer than expected), but Forster’s Terns were not (9 m closer than expected). Our results emphasize the importance of managed ponds for breeding and foraging waterbirds, including islands for breeding and roosting and levees for foraging.

Keywords

birds

waterbirds

Pond Complex

Alviso

Eden Landing

Ravenswood

Content available here

eScholarship link to paper

Monitoring Nesting Waterbirds for the South Bay Salt Pond Restoration Project: 2022 Breeding Season

admin — Wed, 05 Apr 2023 22:28:49 +0000

Monitoring Nesting Waterbirds for the South Bay Salt Pond Restoration Project: 2022 Breeding Season

Figure from: Ackerman, JT, CA Hartman, and MP Herzog. 2023. Monitoring nesting waterbirds for the South Bay Salt Pond Restoration Project: 2022 breeding season. U.S. Geological Survey Open-File Report

admin Wed, 04/05/2023 - 15:28

Document Category

Monitoring Reports

Author(s)

Joshua T. Ackerman

C. Alex Hartman

Mark P. Herzog

Date

2023-04-06

Summary

San Francisco Bay supports thousands of breeding waterbirds annually and historically has hosted large populations of American avocets (Recurvirostra americana), black-necked stilts (Himantopus mexicanus), and Forster’s terns (Sterna forsteri). These three species have relied largely on former agricultural salt ponds in South San Francisco Bay, which provide wetland foraging habitat as well as island nesting habitat. The South Bay Salt Pond Restoration Project is in the process of restoring up to 15,100 acres of these former salt ponds to tidal marsh and tidal mudflats. Although this restoration is expected to have numerous benefits including providing habitat for tidal wetland-dependent species, improved water quality, buffering against storm surge and protecting inland areas from sea level rise, the reduction in former salt pond habitat and nesting islands therein may negatively impact breeding waterbirds. To address this, the South Bay Salt Pond Restoration Project also includes enhancements to remaining pond habitat such as the construction of new islands for nesting. Moreover, the South Bay Salt Pond Restoration Project follows an adaptive management plan in which waterbird response to the changing landscape is monitored over time to ensure that existing breeding waterbird populations are maintained. In this report, we provide results of waterbird nest monitoring in South San Francisco Bay during the 2022 breeding season and present these results in the context of annual nest monitoring in South San Francisco Bay since 2005. Overall nest abundance remained at or near 18-year lows for American avocets (176 nests) and black-necked stilts (97 nests), but Forster’s tern nest abundance (1,727 nests) was at an 18-year high, reversing historically low abundance observed during 2015-2017. In 2022, there were only 6 American avocet, 3 blacknecked stilt, and 4 Forster’s tern major colony nesting sites, down from annual averages of 12.4, 6.6, and 6.6 observed during 2005-2009. Nest success (30% for American avocets, 29% for black-necked stilt, and 53% for Forster’s terns) was below 2005-2007 baseline values established for the South Bay Salt Pond Restoration Project. Average egg hatching success (98%, 100%, and 90%), and clutch sizes (3.68, 3.70, and 2.63 eggs) of American avocets, black-necked stilts, and Forster’s terns, respectively, were similar to values observed during 2005-2010. All three species exhibited notable shifts in nest initiation dates in 2022, with American avocets and Forster’s terns nesting 10-11 days earlier and black-necked stilts nesting 10 days later than during 2005-2010. Finally, the enhanced managed ponds with newly constructed islands (Ponds A16 and SF2) supported 86% of all the Forster’s tern nests recorded in South San Francisco Bay in 2022, the first time these managed ponds have hosted such a substantial number of tern nests.

Table 1: USGS has monitored nesting waterbird populations and their reproductive success in the South Bay Salt Pond Restoration Project area since 2005 (2005-2022). This table represents demographic rates and nesting habitat parameters for American avocets, black-necked stilts, and Forster’s terns in San Francisco Bay during 2022.
Species	Number of nests	Clutch size	Nest success	Egg hatching success	Nest initiation date	Vegetation height (cm) at the nest	Percent vegetation cover at the nest	Percent bare ground at the nest
American avocet	176	3.68 (3.56 - 3.85)	30% (17 - 44%)	98% (95 - 100%)	May 4 (April 9 - June 5)	6.5 (5.8 – 7.3)	41.7% (36.5 – 47.0%)	58.2% (53.2 – 63.2%)
Black-necked stilt	97	3.70 (3.55 - 3.85)	29% (13 - 46%)	100% (100 - 100%)	May 13 (May 1 - June 25)	12.0 (10.4 – 13.5)	77.0% (70.2 – 83.7%)	22.1% (15.7 – 28.6%)
Forster's tern	1727	2.63 (2.56 - 2.69)	53% (41 - 63%)	90% (86% - 93%)	May 20 (May 11 – June 10)	8.0 (7.5 – 8.4)	56.4% (52.8 – 59.9%)	44.1% (40.9 – 47.3%)

Keywords

Pond Complex

Alviso

Eden Landing

Ravenswood

Breeding Waterbird Populations Have Declined in South San Francisco Bay: An Assessment Over Two Decades

ariela — Tue, 28 Sep 2021 17:03:30 +0000

Breeding Waterbird Populations Have Declined in South San Francisco Bay: An Assessment Over Two Decades ariela Tue, 09/28/2021 - 10:03

Document Category

Scientific Reports

Author(s)

Date

2021-09

Summary

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

Pond Complex

Alviso

Eden Landing

Ravenswood

Content available here

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

Establishing Forster’s Tern (Sterna forsteri) Nesting Sites at Pond A16 Using Social Attraction for the South Bay Salt Pond Restoration Project

ariela — Mon, 10 Aug 2020 18:52:54 +0000

Establishing Forster’s Tern (Sterna forsteri) Nesting Sites at Pond A16 Using Social Attraction for the South Bay Salt Pond Restoration Project

Cover of Forster's tern report

ariela Mon, 08/10/2020 - 11:52

Document Category

Scientific Reports

Author(s)

Date

2020-07

Summary

Abstract

Forster’s terns (Sterna forsteri), historically one of the most numerous colonial-breeding waterbirds in South San Francisco Bay, California, have experienced recent decreases in the number of nesting colonies and overall breeding population size. The South Bay Salt Pond Restoration Project aims to restore 50–90 percent of former salt evaporation ponds to tidal marsh habitat in South San Francisco Bay. During phase 1 of the South Bay Salt Pond Restoration Project, the breaching of several pond levees to begin the process of tidal marsh restoration inundated island nesting habitat that had been used by Forster’s terns, American avocets (Recurvirostra americana), and other waterbirds. Additional nesting habitat could be lost as more managed ponds are converted to tidal marsh in the future. To address this issue, the South Bay Salt Pond Restoration Project organized the construction of new nesting islands in managed ponds that will not be restored to tidal marsh, thereby providing enduring island nesting habitat for waterbirds. In 2012, 16 new islands were constructed in Pond A16 in the Alviso complex of the Don Edwards San Francisco Bay National Wildlife Refuge, which increased the number of islands in this pond from 4 to 20. However, despite a long history of nesting on the four islands in Pond A16 before the 2012 construction activities, no Forster’s terns have nested in Pond A16 during the 7-year period (2012–18) after island construction.

During the 2017 and 2019 breeding seasons, we used social attraction measures (decoys and colony call playback systems) to attract Forster’s terns to islands within Pond A16 to re-establish nesting colonies. We maintained these systems from March through August in each year. To evaluate the effect of these social attraction measures, we completed surveys (between April and August) where we recorded the number and location of all Forster’s terns and other waterbirds using Pond A16, and we monitored waterbird nests. We compared bird survey and nest monitoring data collected in 2017 and 2019 to data collected in 2015 and 2016, prior to the implementation of social attraction measures, allowing for direct evaluation of the effect of social attraction efforts on Forster’s terns.

To increase the visibility and stakeholder involvement of this project, we engaged in multiple outreach activities in 2017, 2019, and 2020, including the development of a project website and educational video; publication of popular articles in 2017 and 2020; the development of outreach materials describing the project to the general public; and public presentations to relay findings to managers, stakeholders, and the general public.

The relative abundance of Forster’s terns in Pond A16, after adjusting for the overall South San Francisco Bay breeding population each year, was higher during the nesting period in 2017 and 2019 (when social attraction was used) than in 2015 and 2016 (before social attraction was used). Furthermore, more Forster’s terns were observed during the pre-nesting and nesting periods in the areas of Pond A16 where decoys and call systems were deployed. Although no Forster’s tern nests were observed in Pond A16 before social attraction was implemented (2015, 2016), or during the first-year social attraction was implemented (2017), 35 Forster’s tern nests were recorded during the second year of social attraction implementation in 2019. These 35 nests represent a re-establishment of a Forster’s tern nesting colony to Pond A16 for the first time in 8 years. As social attraction efforts often benefit from multiple years of decoy and call system deployment, results from 2017 and 2019 suggest that continued implementation of social attraction measures could help to ensure Forster’s tern breeding colonies persist in Pond A16 and other areas of South San Francisco Bay.

Suggested Citation

Hartman, C.A., Ackerman, J.T., Herzog, M.P., Wang, Y., and Strong, C., 2020, Establishing Forster’s Tern (Sterna forsteri) nesting sites at pond A16 using social attraction for the South Bay Salt Pond restoration project: U.S. Geological Survey Open-File Report 2020–1081, 28 p., https://doi.org/10.3133/ofr20201081.

ISSN: 2331-1258 (online)

Keywords

Pond Complex

Alviso

Evaluation of social attraction measures to establish Forster's tern (Sterna forsteri) nesting colonies for the South Bay Salt Pond Restoration Project, San Francisco Bay, California--2017 Annual Report

Dave Halsing — Wed, 22 Jan 2020 21:05:37 +0000

Evaluation of social attraction measures to establish Forster's tern (Sterna forsteri) nesting colonies for the South Bay Salt Pond Restoration Project, San Francisco Bay, California--2017 Annual Report Dave Halsing Wed, 01/22/2020 - 13:05

Document Category

Scientific Reports

Author(s)

Date

2018-05-31

Keywords

Forster’s tern

social attraction

nesting density

Pond Complex

Alviso

Content available here

USGS Publications

Egg turning behavior and incubation temperature in Forster's terns in relation to mercury contamination

Dave Halsing — Wed, 22 Jan 2020 20:56:58 +0000

Egg turning behavior and incubation temperature in Forster's terns in relation to mercury contamination Dave Halsing Wed, 01/22/2020 - 12:56

Document Category

Scientific Reports

Author(s)

Gregory T. Taylor

Joshua T. Ackerman

Scott A. Shaffer

Date

2018-02-15

Keywords

Forster’s tern

bird eggs

mercury

Pond Complex

Alviso

Ravenswood

Content available here

PLOS One Website

Prey fish returned to Forster's tern colonies suggest spatial and temporal differences in fish composition and availability

Dave Halsing — Wed, 22 Jan 2020 20:35:26 +0000

Prey fish returned to Forster's tern colonies suggest spatial and temporal differences in fish composition and availability Dave Halsing Wed, 01/22/2020 - 12:35

Document Category

Scientific Reports

Author(s)

Sarah H. Peterson

Joshua T. Ackerman

Collin A. Eagles-Smith

Mark P. Herzog

C. Alex Hartman

Date

2018-03-15

Keywords

Forster’s tern

waterbirds

Pond Complex

Alviso

Eden Landing

Ravenswood

Content available here

PLOS One Website

Calabazas-San Tomas Aquino Pond A8 reconnection: Preliminary scenario simulations

Biruk — Mon, 21 Oct 2019 16:18:28 +0000

Calabazas-San Tomas Aquino Pond A8 reconnection: Preliminary scenario simulations Biruk Mon, 10/21/2019 - 09:18

Document Category

Scientific Reports

Author(s)

Björn R. Röbke

Mick van der Wegen

Date

2018

Keywords

Pond Complex

Alviso

Waterbird Nest-Site Selection is Influenced by Neighboring Nests and Island Topography

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

Waterbird Nest-Site Selection is Influenced by Neighboring Nests and Island Topography admin Wed, 11/22/2017 - 16:21

Document Category

Scientific Reports

Author(s)

Date

2016

Keywords

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

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

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