American avocet

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

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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%)