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USGS2002

Waterbird conservation for the Americas: The North American waterbird conservation plan, version 1

The North American Waterbird Conservation Plan (the Plan) is the product of an independent partnership of individuals and institutions having interest and responsibility for conservation of waterbirds and their habitats in the Americas. This partnership - Waterbird Conservation for the Americas - was created to support a vision in which the distribution, diversity, and abundance of populations and habitats of breeding, migratory, and nonbreeding waterbirds are sustained or restored throughout the lands and waters of North America, Central America, and the Caribbean. The Plan provides a continental-scale framework for the conservation and management of 210 species of waterbirds, including seabirds, coastal waterbirds, wading birds, and marshbirds utilizing aquatic habitats in 29 nations throughout North America, Central America, the islands and pelagic waters of the Caribbean Sea and western Atlantic, the U.S.-associated Pacific Islands and pelagic inland and pelagic waters of the Pacific. Birds as familiar as herons, loons, pelicans, and gulls, as well as the lesser known albatrosses, petrels, auks, and rails are among the species considered in the Plan. These birds' dependence on aquatic habitats such as wooded swamps, stream corridors, salt marshes, barrier islands, continental shelf waters and open pelagic waters make them especially vulnerable to the myriad threats facing water and wetland resources globally. In addition, the congregatory behavior of many waterbirds increases population risks by concentrating populations in limited areas.

Book↗

USGS2012

Waterbird nest monitoring program in San Francisco Bay (2005-10)

Historically, Forster’s Terns ( Sterna forsteri ), American Avocets ( Recurvirostra americana ), and Black-necked Stilts ( Himantopus mexicanus ) were uncommon residents of San Francisco Bay, California (Grinnell and others, 1918; Grinnell and Wythe, 1927; Sibley, 1952). Presently, however, avocets and stilts are the two most abundant breeding shorebirds in San Francisco Bay (Stenzel and others, 2002; Rintoul and others, 2003). More than 4,000 avocets and 1,000 stilts, roughly 20 percent of their San Francisco Bay wintering populations, breed within the estuary, making San Francisco Bay the largest breeding area for these species on the Pacific Coast (Stenzel and others, 2002; Rintoul and others, 2003). Forster’s Terns were first observed breeding in the San Francisco Bay in 1948 (110 nests); they had increased to over 4000 individuals by the 1980s (Sibley, 1952; Gill, 1977; Harvey and others, 1992; Carter and others, 1990) and were estimated at 2000–3000 for 1998–2002; (Strong and others, 2004). It is hypothesized that the relatively large size of the current waterbird breeding populations is a result of the creation of artificial salt evaporation ponds from the 1930s through the 1950s (Gill, 1977; Goals Project, 1999). Until recently, these salt ponds and associated islands used by waterbirds for nesting have been managed relatively similarly and have supported large breeding waterbird populations. Recently, the South Bay Salt Pond Restoration Project has implemented plans to convert 50–90 percent of the 15,000 acres of salt ponds in the South San Francisco Bay back to tidal marsh habitat. Therefore, there is concern that the Restoration Project, while benefiting other native species, could negatively influence local breeding populations of waterbirds that are reliant on salt pond habitats for both breeding and foraging. A primary goal of the South Bay Salt Pond Restoration Project is to maintain current breeding waterbird populations (South Bay Salt Pond Long-Term Restoration Project, 2004); thus, specific efforts are planned to ensure that the Restoration Project enhances the habitats of the remaining salt ponds for breeding waterbirds. Here, we provide a summary of nesting ecology data for Forster’s Terns, American Avocets, and Black-necked Stilts, collected from 2005 to 2010 in the areas of the South Bay Salt Pond Restoration Project, including lands managed by the Don Edwards San Francisco Bay National Wildlife Refuge and Eden Landing Ecological Reserve. These results provide baseline conditions for breeding waterbirds prior to implementation of most restoration actions and can be used to both guide future restoration actions as well as to determine the effect of the South Bay Salt Pond Restoration Project on breeding waterbirds. It is imperative to continue to collect nesting waterbird data annually to assess the response of birds to the South Bay Salt Pond Restoration Project.

California↗

USGS2021

Aerial strip-transect surveys: Indexing autumn–winter waterbird abundance and distribution in South Carolina

Aerial surveys integrating probability-based sample designs have been implemented successfully to estimate relative abundance of wintering ducks in Arkansas, Louisiana, Mississippi, and Missouri, but these approaches have not been evaluated in the Atlantic Flyway except for American black ducks ( Anas rubripes ) along the Atlantic coast. Furthermore, these surveys have not been used to index abundance of other nonbreeding waterbirds. Given elimination or reduction of resources allocated to the Midwinter Waterfowl Survey in the Atlantic Flyway and elsewhere, the South Carolina Department of Natural Resources (SCDNR) expressed a need for reliable surveys to monitor waterfowl and other waterbirds during autumn through winter. We designed stratified aerial strip-transect surveys to estimate population indices for migrating and wintering dabbling ducks (Anatini), diving ducks (Aythini, Mergini, Oxyurini), pelagic and piscivorous waterbirds (Anhingidae, Laridae, Pelicanidae, Phalacrocoracidae), and wading birds (Ardeidae, Ciconiidae, Threskiornithidae) in coastal and inland regions of South Carolina during autumn-winter 2017–2019. We used unequal probability random sampling to estimate population indices with deemed adequate precision (i.e., coefficient of variation [CV] ≤ 20%) and estimated theoretical survey efforts needed to achieve desired precision for future aerial surveys. Indices met our goal for precision in September and January 2018 for wading birds, in February and November 2018 for pelagic waterbirds, and in February 2018 for diving ducks, but never for other ducks during South Carolina waterfowl hunting season. We detected peak abundance of dabbling and diving ducks in January and wading birds and wood storks ( Mycteria americana ) in September. We estimated ~2.5 times greater survey effort was needed across waterbird taxa than was expended to achieve a CV=20%. We also used survey data to depict spatiotemporal variation in waterbird distributions across the study area. Our surveys are applicable for the SCDNR and other agencies seeking to monitor autumn-winter waterbird populations. Although survey refinements are necessary to increase precision in South Carolina, our waterbird indices are useful to assess population trends through time, guide habitat management and restoration efforts, refine local harvest regulations, inform law enforcement to detected illicit activities (e.g., baiting), and monitor possible shifting waterbird distributions in response to land-use and climate change.

South Carolina↗

USGS2015

Waterbird use of catfish ponds and migratory bird habitat initiative wetlands in Mississippi

Aquaculture can provide important surrogate habitats for waterbirds. In response to the 2010 Deepwater Horizon oil spill, the National Resource Conservation Service enacted the Migratory Bird Habitat Initiative through which incentivized landowners provided wetland habitats for migrating waterbirds. Diversity and abundance of waterbirds in six production and four idled aquaculture facilities in the Mississippi Alluvial Valley were estimated during the winters of 2011–2013. Wintering waterbirds exhibited similar densities on production (i.e., &sim;22 birds/ha) and idled (i.e., &sim;20 birds/ha) sites. A total of 42 species were found using both types of aquaculture wetlands combined, but there was considerable departure in bird guilds occupying the two wetland types. The primary users of production ponds were diving and dabbling ducks and American coots. However, idled ponds, with varying water depths (e.g., mudflats to 20 cm) and diverse emergent vegetation-water interspersion, attracted over 30 species of waterbirds and, on average, had more species of waterbirds from fall through early spring than catfish production ponds. Conservation through the Migratory Bird Habitat Initiative was likely responsible for this difference. Our results suggest production and idled Migratory Bird Habitat Initiative aquaculture impoundments produced suitable conditions for various waterbird species and highlight the importance of conservation programs on private lands that promote diversity in vegetation structure and water depths to enhance waterbird diversity.

Mississippi↗

USGS1996

Effects of a legal drain clean-out on wetlands and waterbirds: a recent case history

Repairs to legal drains in the United States may be regulated to protect adjacent wetlands under Section 404 of the Federal Water Pollution Control Act, commonly known as the Clean Water Act (CWA). However, few studies have examined effects of legal drain clean-outs on adjacent wetlands and associated migratory waterbird populations. I compare water regimes, cover-to-open water ratios, and waterbird use on Bruns, Big, Meszaros, and Kraft sloughs (BBMK) in Sargent County, North Dakota before and after the clean-out of Crete-Cogswell Drain No. 11, and relate wetland habitat loss to observed disease-related mortality among staging waterfowl in fall 1990 and spring 1991. Water regimes of BBMK were exceptionally stable, with few records of drawdowns before 1984 when the clean-out began. After the clean-out (1987-90), BBM were dry by mid-summer in all years and open area declined by 96% by 1990, whereas Kraft Slough (a control area) had water throughout all years and percent open area did not change. Numerous species of waterbirds nested in BBMK before the clean-out, and mean ranks of waterbird density were similar. After the clean-out, waterbirds failed to breed successfully in all years at BBM, and use as major waterfowl staging areas and for waterfowl hunting also ended. At Kraft Slough, use by breeding and staging waterbirds continued in all years, as did waterfowl hunting. Reduced access to fresh water after the Drain No. 11 clean-out may have contributed to a dieoff of 487 lesser snow geese (Chen caerulescens) from necrotic enteritis in Kraft Slough in November 1990. Loss of three major staging areas in Sargent County as a result of the drain clean-out has further concentrated migrant waterfowl, particularly during drought periods, increasing the magnitude of risk when epizootics occur in southeastern North Dakota. Ducks and geese banded in Sargent County have been recovered from 34 and 14 states, 7 and 6 provinces of Canada, and 13 and 1 other countries, respectively, indicating waterfowl populations from a wide area are potentially vulnerable to epizootics when crowded into limited roosting habitat. Despite causing the loss of wetland habitat for thousands of midcontinent waterfowl and other waterbirds, a Federal Court in North Dakota ruled that the clean-out of Drain No. 11 met the criteria necessary to be considered maintenance under Section 404 clause (f)(1)(c) and was not recaptured under clause (f)(2). This outcome suggests current law does not protect wetland functions needed to support migratory waterbird populations or associated recreational values when sites have become naturally restored through lack of maintenance of legal drains.

Wetlands↗

USGS2017

Projected impacts of climate, urbanization, water management, and wetland restoration on waterbird habitat in California’s Central Valley

The Central Valley of California is one of the most important regions for wintering waterbirds in North America despite extensive anthropogenic landscape modification and decline of historical wetlands there. Like many other mediterranean-climate ecosystems across the globe, the Central Valley has been subject to a burgeoning human population and expansion and intensification of agricultural and urban development that have impacted wildlife habitats. Future effects of urban development, changes in water supply management, and precipitation and air temperature related to global climate change on area of waterbird habitat in the Central Valley are uncertain, yet potentially substantial. Therefore, we modeled area of waterbird habitats for 17 climate, urbanization, water supply management, and wetland restoration scenarios for years 2006–2099 using a water resources and scenario modeling framework. Planned wetland restoration largely compensated for adverse effects of climate, urbanization, and water supply management changes on habitat areas through 2065, but fell short thereafter for all except one scenario. Projected habitat reductions due to climate models were more frequent and greater than under the recent historical climate and their magnitude increased through time. After 2065, area of waterbird habitat in all scenarios that included severe warmer, drier climate was projected to be >15% less than in the “existing” landscape most years. The greatest reduction in waterbird habitat occurred in scenarios that combined warmer, drier climate and plausible water supply management options affecting priority and delivery of water available for waterbird habitats. This scenario modeling addresses the complexity and uncertainties in the Central Valley landscape, use and management of related water supplies, and climate to inform waterbird habitat conservation and other resource management planning. Results indicate that increased wetland restoration and additional conservation and climate change adaptation strategies may be warranted to maintain habitat adequate to support waterbirds in the Central Valley.

California↗

USGS2020

Shallow lake management enhanced habitat and attracted waterbirds during fall migration

Lake water levels are often managed in shallow lakes in order to improve water quality and promote aquatic vegetation that presumably benefits water birds. We aimed to understand whether waterbird abundance and species richness during fall migrations were positively influenced by managed lake water levels at 32 shallow lakes over 10 years. We conducted annual waterbird surveys that totaled 6 million birds counted and we repeatedly measured several in-lake habitat variables. Lakes with water level management had lower water depths, greater water quality and clarity, more submerged aquatic vegetation (SAV), and more wild rice (Zizania palustris) compared to unmanaged lakes. Redundancy analysis and regressions revealed that the waterbird community and several waterbird species were positively correlated to water level management and SAV; however, waterbirds were apparently responding principally to abundant SAV regardless of water depth or management. Two presented case studies of turbid-state lakes also highlighted that water level management rehabilitated lake habitat and waterbird use for a few years. We concluded that water level management can be an effective tool for increasing SAV and migrating waterbirds but noted large bird communities can also occur on unmanaged, deeper wetlands with existing SAV coverage of >80%.

Minnesota↗

USGS2017

Effects of local shoreline and subestuary watershed condition on waterbird community integrity: Influences of geospatial scale and season in the Chesapeake Bay

In many coastal regions throughout the world, there is increasing pressure to harden shorelines to protect human infrastructures against sea level rise, storm surge, and erosion. This study examines waterbird community integrity in relation to shoreline hardening and land use characteristics at three geospatial scales: (1) the shoreline scale characterized by seven shoreline types: bulkhead, riprap, developed, natural marsh, Phragmites- dominated marsh, sandy beach, and forest; (2) the local subestuary landscape scale including land up to 500 m inland of the shoreline; and (3) the watershed scale >500 m from the shoreline. From 2010 to 2014, we conducted waterbird surveys along the shoreline and open water within 21 subestuaries throughout the Chesapeake Bay during two seasons to encompass post-breeding shorebirds and colonial waterbirds in late summer and migrating and wintering waterfowl in late fall. We employed an Index of Waterbird Community Integrity (IWCI) derived from mean abundance of individual waterbird species and scores of six key species attributes describing each species’ sensitivity to human disturbance, and then used this index to characterize communities in each subestuary and season. IWCI scores ranged from 14.3 to 19.7. Multivariate regression model selection showed that the local shoreline scale had the strongest influence on IWCI scores. At this scale, percent coverage of bulkhead and Phragmites along shorelines were the strongest predictors of IWCI, both with negative relationships. Recursive partitioning revealed that when subestuary shoreline coverage exceeded thresholds of approximately 5% Phragmites or 8% bulkhead, IWCI scores decreased. Our results indicate that development at the shoreline scale has an important effect on waterbird community integrity, and that shoreline hardening and invasive Phragmites each have a negative effect on waterbirds using subestuarine systems.

Chesapeake Bay↗

USGS2023

Habitat use by breeding waterbirds in relation to tidal marsh restoration in the San Francisco Bay estuary

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.

California↗

USGS1996

The relevance of the Mediterranean Region to colonial waterbird conservation

The Mediterranean Sea is the largest partially enclosed sea in the world and provides habitat to more than 100 species of waterbirds from the Palearctic-North African-Middle Eastern regions. Even though the Mediterranean suffers from pollution, has little tidal influence, and is oligotrophic, more than half of the western Palearctic populations of numerous waterfowl species winter in the region. Thirty-three species of colonial waterbirds breed along the 46,000 km Mediterranean coastline with nine species considered threatened or endangered, mostly because of wetland loss and degradation. The long history of human activity and scientific investigations in the region has taught some valuable lessons. In the area of colonial waterbird biology and conservation, we have learned important lessons about the value of long-term monitoring and research on selected populations. From marking studies of Greater Flamingos (Phoenicopterus ruber roseus) and Little Egrets (Egretta garzetta) results have been used to derive useful information about metapopulation dynamics. Involvement of both African and European biologists allowed year-round Studies of these species that yielded valuable spin-offs for training in avian and wetland conservation. We have also learned the value of man-made wetlands as feeding and nesting sites for some colonial waterbirds. Careful evaluations of the habitat quality of different types of wetlands are required, as in contaminant levels such as lead shot and pesticides. Wetland conservationists have also learned from some instructive mistakes. Dam construction and agricultural incentive programs sponsored by the European Community, the World Bank, and others from the past have largely ignored impacts on wetlands and wildlife. In some areas, economic ventures such as aquaculture operations and salt mining have not involved waterbird habitat needs in their planning. Research and conservation needs include: (1) establishing regional monitoring programs and data banks for seabirds, wading birds, ducks, and geese; (2) implementing a wetland inventory for many Countries with little quantitative data on wetlands; (3) improving habitat quality assessments; (4) improving relationships with industry, the private citizenry, and government officials to further an appreciation for the value of wetlands and waterbirds; (5) enhancing training efforts, especially in underdeveloped Countries; (6) evaluating the effects of hunting and other disturbances to nesting and feeding waterbirds in different regions; (7) setting up 'sister-reserve' (twinned) sites in Europe and Africa to foster international linkages and training; and (8) fostering local-regional conservation programs to preserve reed beds, wet woodlots, and other key habitats.

Book chapter↗

USGS2026

Global change and threats to waterbirds in the Asian flyways

Avian migration represents one of nature’s most spectacular phenomena, providing critical ecological services and acting as an indicator of environmental change. Flyways are geographical ranges through which migrating bird species move, and the flyway concept has been used to identify countries that share species to highlight their collective responsibility for conservation. Of the nine recognized global waterbird flyways, the Central Asian Flyway (CAF) and the East Asian–Australasian Flyway (EAAF) are among the most important areas in Eurasia, supporting millions of waterbirds across a vast network of habitats. We proposed this special issue in Avian Research entitled “Global Change and Threats to Waterbirds in the Asian Flyways” to synthesize recent findings from 12 papers covering a wide range of topics. The CAF stretches from the Siberian tundra through Central Asia including Mongolia, the Qinghai-Tibet Plateau, the Trans-Caucasus, and the Himalayas, extending south to the Indian subcontinent and parts of the Middle East. The EAAF spans eastern Siberia and Alaska to Southeast Asia, Australia, and New Zealand, including China, Japan, the Korean Peninsula, and the Russian Far East. These two flyways include 47 countries comprising critical wetlands, river basins, and coastal areas, which are vital breeding, stopover, and wintering grounds for waterbirds. Seasonal migration in these flyways is fundamentally influenced by climate and weather conditions, land cover dynamics, and anthropogenic activities, and contributes significantly to ecological processes such as pest control, nutrient cycling, and organism dispersal. However, migratory waterbirds and their habitats are undergoing enormous challenges. Changes in climate, habitat availability and connectivity, and human activities are altering the phenology, distribution, population dynamics, and health of the migratory bird populations. As migratory waterbirds travel across international boundaries, understanding their movements and responses to environmental change requires collaborative, cross-border research efforts that promote knowledge sharing and interdisciplinary approaches.

Avian Research↗

USGS2023

Monitoring nesting waterbirds for the South Bay Salt Pond Restoration Project—2022 breeding season

The San Francisco Bay supports thousands of breeding waterbirds annually and hosts 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 commercial salt ponds in South San Francisco Bay, which provide wetland foraging habitat and island nesting habitat. The South Bay Salt Pond Restoration Project is in the process of restoring 50–90 percent of 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, improving water quality, buffering against storm surge, and protecting inland areas from sea level rise, the reduction in former salt pond habitat and nesting islands may negatively affect breeding waterbirds. To address the reduction in former salt pond habitat available to waterbirds, 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 in 2022 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, 4 black-necked stilt, and 4 Forster’s tern major colony nesting sites, which is down from annual averages of 12.4, 6.6, and 6.6 observed during 2005–2009. Nest success (30 percent for American avocets, 29 percent for black-necked stilt, and 53 percent for Forster’s terns) was below the 2005–2007 baseline values established for the South Bay Salt Pond Restoration Project. Average egg-hatching success (98 percent, 100 percent, and 90 percent), 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 displayed 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 percent of all the Forster’s tern nests recorded in South San Francisco Bay in 2022, which is the first time these managed ponds have hosted such a substantial number of tern nests.

California↗

USGS2026

Monitoring nesting waterbirds for the South Bay Salt Pond Restoration Project—2024 breeding season

The San Francisco Bay supports thousands of breeding waterbirds annually and hosts 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 commercial salt ponds in south San Francisco Bay, which provide wetland foraging habitat and island nesting habitat. The South Bay Salt Pond Restoration Project is in the process of restoring as much as 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, improving water quality, buffering against storm surge, and protecting inland areas from sea level rise, the reduction in former salt-pond habitat and nesting islands may negatively affect breeding waterbirds. To address the reduction in former salt-pond habitat available to waterbirds, the South Bay Salt Pond Restoration Project will maintain some pond habitat for wildlife and provide enhancements such as the construction of new islands for nesting. 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 2024 breeding season and present these results in the context of annual nest monitoring in south San Francisco Bay since 2005. Overall, Forster’s tern nest abundance in 2024 (1,808 nests) was the highest recorded between 2005 and 2024, and it maintained the high abundance first observed in 2022 (1,727 nests), which reversed the historically low abundance observed during 2015–17. In contrast, nest abundance remained at or near 20-year lows for American avocets (222 nests) and black-necked stilts (126 nests) in 2024, but both species had small increases in their nesting population sizes compared to 2022. In 2024, there were only 3 Forster’s tern, 5 American avocet, and 3 black-necked stilt major colony nesting sites, which is down from the annual averages of 6.6, 12.4, and 6.6 observed during 2005–09. Nest success (73 percent for American avocets, 54 percent for black-necked stilt, and 64 percent for Forster’s terns) increased compared to 2022 (30 percent for American avocets, 29 percent for black-necked stilt, and 53 percent for Forster’s terns) and during 2005–10 (37 percent for American avocets, 24 percent for black-necked stilt, and 61 percent for Forster’s terns). Nest success in 2024 was above (American avocets and black-necked stilts) or slightly below (Forster’s terns) baseline values established for the South Bay Salt Pond Restoration Project. Average egg-hatching success was lower for American avocets (86 percent) and Forster’s terns (86 percent) and similar for black-necked stilts (96 percent) than the values observed during 2005–10. Average clutch sizes for American avocets (3.87 eggs), black-necked stilts (3.88 eggs), and Forster’s terns (2.73 eggs) were greater than what was observed in 2022 and during 2005–10. Average nest-initiation dates in 2024 were substantially earlier among all three species (April 19 for American avocets, April 25 for black-necked stilts, and May 12 for Forster’s terns) than in 2022 (May 4 for American avocets, May 13 for black-necked stilts, and May 20 for Forster’s terns) and during 2005–10 (May 15 for American avocets, May 3 for black-necked stilts, and May 30 for Forster’s terns). Finally, the enhanced managed ponds with newly constructed islands (Ponds A16 and SF2) supported 52 percent of American avocet nests, 47 percent of black-necked stilt nests, and 94 percent of all the Forster’s tern nests recorded in south San Francisco Bay in 2024.

California↗

USGS2013

Changes in types and area of postharvest flooded fields available to waterbirds in Tulare Basin, California

Conservation efforts to restore historic waterbird distribution and abundance in the Central Valley of California require information on current and historic areas of waterbird habitat. To provide this information, we mapped the area of agricultural fields in the vicinity of the historic Tulare Lake Bed in the Tulare Basin, California, that were treated postharvest with two different flooding regimes that varied in depth and duration of water applied (, 1 cm to 1.5 m water for longer than 1 wk [FLD]; , 1 to 15 cm water for 1 wk or less [IRG]) during August–March 1991–1994 and 2005–2006. We compared our results with published estimates for 1976–1980 and 1981–1987. Area and crops treated postharvest with FLD or IRG flooding differed among years and months. Overall for August through March, weekly area of FLD fields averaged 1,671 ha in 1976–1980 but declined to about half that in later years; the decline was most severe during January–March. Cotton was primarily treated with IRG flooding and comprised 47–95% of the total IRG field area. Other crops were primarily treated with FLD flooding; tomato replaced safflower in 2005–2006. These documented declines since the 1970s in area of FLD fields and changes in crops being flooded postharvest reduce the carrying capacity of the Tulare Basin for waterbirds, a situation that will need to be reversed for restoration of historic waterbird distribution in the Central Valley to be viable. If maintaining agricultural production is a priority and agricultural drainage waters can be disposed of safely, then increasing the extent of FLD grain fields would provide the most benefit for wintering waterbirds; otherwise, restoring and providing adequate water supplies to managed wetlands would most benefit waterbirds

California↗

USGS1995

Colonial waterbirds

Colonial waterbirds, that is, seabirds (gulls, terns, cormorants, pelicans) and wading birds (herons, egrets, ibises), have attracted the attention of scientists, conservationists, and the public since the turn of the century when plume hunters nearly drove many species to extinction. The first national wildlife refuge at Pelican Island, Florida, was founded to conserve a large nesting colony of the brown pelican ( Pelecanus occidentalis ). The National Audubon Society also established a game warden system to monitor and protect important waterbird colonies. These efforts helped establish federal laws to protect migratory birds and their nesting habitats in North America. Although the populations of many species rebounded in the early part of the 20th century, major losses and alteration of coastal wetlands still threaten the long-term sustainability of many colonial waterbirds. A national, coordinated monitoring program is needed to monitor population status and trends in colonial waterbirds (Erwin et al. 1993). The Canadian Wildlife Service has recently established a national seabird monitoring program (D. Nettleship, CWS, personal communication). In addition, better coordination and cooperation for monitoring waterbirds are needed on both their breeding grounds in North America and their wintering grounds in Latin America where wetland loss is also a critical problem (Erwin et al. 1993). This article summarizes the status and trends of selected waterbird species in North America, but excludes Alaska, Hawaii, and the Pacific coast, which are described elsewhere.

Book chapter↗

USGS2025

Habitat features influencing waterbird use of managed wetlands enrolled in a public-private partnership for land conservation: The California Waterfowl Habitat Program

Draining, water diversion, and development have greatly reduced the availability of freshwater wetland habitat around the world, and many remaining wetlands are on private lands. Public–private partnership programs can be an important means for promoting habitat conservation and management on private lands. We investigated bird use of 117 wetlands enrolled in the California Waterfowl Habitat Program in California's Central Valley, where two-thirds of wetlands are under private ownership and management. Specifically, we quantified the influence of wetland habitat features and surrounding land cover on waterbird density and diversity in late winter and early spring and during the waterfowl breeding season. Dabbling duck and shorebird densities were highest in wetlands that had water depths < 20 cm, and waterbird densities decreased with water depth. Greater amounts of emergent vegetation, especially tall and dense emergent vegetation, had a negative effect on total waterbird density but a positive effect on species richness and secretive marsh bird density. Shorebird and breeding duck densities were lower in wetlands with a large number of trees and other potential perch sites, and waterbird densities decreased with the amount of nearby wetland habitat on the landscape. Overall, we estimated that during late winter and early spring, private properties that were enrolled in the California Waterfowl Habitat Program (8000–8500 ha each year) supported 480,000 birds per day during extreme drought conditions in 2022 and 280,000 birds per day in more normal, non-drought conditions in 2023. Over the 76-day winter and early spring survey period, this amounted to more than 20 million bird use days on wetlands enrolled in the California Waterfowl Habitat Program during late winter and early spring. These results demonstrate the value of public–private wetland conservation partnerships, the influence of wetland habitat features and surrounding land cover on waterbird abundance, and the benefits of habitat features that could be incorporated into management plans and wetland selection criteria for enrollment into public–private conservation programs.

California↗

USGS2016

Island characteristics within wetlands influence waterbird nest success and abundance

Coastal waterbird populations are threatened by habitat loss and degradation from urban and agricultural development and forecasted sea level rise associated with climate change. Remaining wetlands often must be managed to ensure that waterbird habitat needs, and other ecosystem functions, are met. For many waterbirds, the availability of island nesting habitat is important for conserving breeding populations. We used linear mixed models to investigate the influence of pond and island landscape characteristics on nest abundance and nest success of American avocets ( Recurvirostra americana ), black-necked stilts ( Himantopus mexicanus ), and Forster's terns ( Sterna forsteri ) in San Francisco Bay, California, USA, based on a 9-year dataset that included >9,000 nests. Nest abundance and nest success were greatest within ponds and on individual islands located either <1 km or >4 km from San Francisco Bay. Further, nest abundance was greater within ponds with relatively few islands, and on linear-shaped, highly elongated islands compared to more rounded islands. Nest success was greater on islands located away from the nearest surrounding pond levee. Compared to more rounded islands, linear islands contained more near-water habitat preferred by many nesting waterbirds. Islands located away from pond levees may provide greater protection from terrestrial egg and chick predators. Our results indicate that creating and maintaining a few, relatively small, highly elongated and narrow islands away from mainland levees, in as many wetland ponds as possible would be effective at providing waterbirds with preferred nesting habitat.

California↗

USGS2015

Species richness and distributions of boreal waterbirds in relation to nesting and brood-rearing habitats

Identification of ecological factors that drive animal distributions allows us to understand why distributions vary temporally and spatially, and to develop models to predict future changes to populations–vital tools for effective wildlife management and conservation. For waterbird broods in the boreal forest, distributions are likely driven by factors affecting quality of nesting and brood-rearing habitats, and the influence of these factors may extend beyond singles species, affecting the entire waterbird community. We used occupancy models to assess factors influencing species richness of waterbird broods on 72 boreal lakes, along with brood distributions of 3 species of conservation concern: lesser scaup ( Aythya affinis ), white-winged scoters ( Melanitta fusca ), and horned grebe ( Podiceps auritus ). Factors examined included abundance of invertebrate foods (Amphipoda, Diptera, Gastropoda, Hemiptera, Odonata), physical lake attributes (lake area, emergent vegetation), water chemistry (nitrogen, phosphorus, chlorophyll a concentrations), and nesting habitats (water edge, non-forest cover). Of the 5 invertebrates, only amphipod density was related to richness and occupancy, consistently having a large and positive relationship. Despite this importance to waterbirds, amphipods were the most patchily distributed invertebrate, with 17% of the study lakes containing 70% of collected amphipods. Lake area was the only other covariate that strongly and positively influenced species richness and occupancy of scaup, scoters, and grebes. All 3 water chemistry covariates, which provided alternative measures of lake productivity, were positively related to species richness but had little effect on scaup, scoter, and grebe occupancy. Conversely, emergent vegetation was negatively related to richness, reflecting avoidance of overgrown lakes by broods. Finally, nesting habitats had no influence on richness and occupancy, indicating that, at a broad spatial scale, brood distributions are largely driven by the presence of quality brood-rearing lakes, not nesting habitats. Our findings are relevant to generating conservation plans or management goals; specifically, boreal lakes with abundant amphipods and surface areas >25 ha are important habitat for waterbird broods and merit conservation, especially given the patchy distribution of amphipods. Moreover, these high quality brood-rearing lakes are much rarer, and thus more constraining, than are quality nesting habitats, which are likely abundant in the boreal.

Alaska↗