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USGS2022

Underwater hearing in sea ducks with applications for reducing gillnet bycatch through acoustic deterrence

As diving foragers, sea ducks are vulnerable to underwater anthropogenic activity, including ships, underwater construction, seismic surveys and gillnet fisheries. Bycatch in gillnets is a contributing source of mortality for sea ducks, killing hundreds of thousands of individuals annually. We researched underwater hearing in sea duck species to increase knowledge of underwater avian acoustic sensitivity and to assist with possible development of gillnet bycatch mitigation strategies that include auditory deterrent devices. We used both psychoacoustic and electrophysiological techniques to investigate underwater duck hearing in several species including the long-tailed duck ( Clangula hyemalis ), surf scoter ( Melanitta perspicillata ) and common eider ( Somateria mollissima ). Psychoacoustic results demonstrated that all species tested share a common range of maximum auditory sensitivity of 1.0–3.0 kHz, with the long-tailed ducks and common eiders at the high end of that range (2.96 kHz), and surf scoters at the low end (1.0 kHz). In addition, our electrophysiological results from 4 surf scoters and 2 long-tailed ducks, while only tested at 0.5, 1 and 2 kHz, generally agree with the audiogram shape from our psychoacoustic testing. The results from this study are applicable to the development of effective acoustic deterrent devices or pingers in the 2–3 kHz range to deter sea ducks from anthropogenic threats.

Journal of Experimental Biology↗

USGS1982

Pharmacokinetics and tissue concentrations of tylosin in selected avian species

Tissue and plasma concentrations and the biological half-life of tylosin in avian species of a variety of body sizes and metabolic rates were studied. The species chosen were eastern bobwhite quail (Colinus virginianus virginianus), pigeons (Columba livia), greater sandhill cranes (Grus canadensis tabida), and emus (Dromaius novaehollandiae). In the 1st phase of this study, tylosin was administered IM to quail, pigeons, and emus at a dosage rate of 25 mg/kg of body weight and to cranes at a dosage rate of 15 mg/kg. The average peak plasma concentrations of tylosin in quail, pigeons, cranes, and emus were 4.31, 5.63, 3.62, and 3.26 microgram/ml, respectively. These peak concentrations occurred at 0.5 to 1.5 hours after administration. The biological half-life of tylosin averaged 1.2 hours in quail, pigeons, and cranes, and was 4.7 hours in emus. In the 2nd phase of this study, tylosin concentrations in the tissues of quail, pigeons, and cranes were markedly higher than were plasma concentrations at corresponding sampling times. Six hours after antibiotic administration, tissue concentrations of tylosin in all species remained within the minimum inhibitory concentration for most pathogenic organisms. Dosage regimens of 25 mg of tylosin/kg 4 times daily for quail and pigeons, 15 mg/kg 3 times daily for cranes, and 25 mg/kg 3 times daily for emus would be needed to establish and maintain therapeutic tissue concentrations.

American Journal of Veterinary Research↗

USGS2008

Avian movements and wetland connectivity in landscape conservation

The current conservation crisis calls for research and management to be carried out on a long-term, multi-species basis at large spatial scales. Unfortunately, scientists, managers, and agencies often are stymied in their effort to conduct these large-scale studies because of a lack of appropriate technology, methodology, and funding. This issue is of particular concern in wetland conservation, for which the standard landscape approach may include consideration of a large tract of land but fail to incorporate the suite of wetland sites frequently used by highly mobile organisms such as waterbirds (e.g., shorebirds, wading birds, waterfowl). Typically, these species have population dynamics that require use of multiple wetlands, but this aspect of their life history has often been ignored in planning for their conservation. We outline theoretical, empirical, modeling, and planning problems associated with this issue and suggest solutions to some current obstacles. These solutions represent a tradeoff between typical in-depth single-species studies and more generic multi-species studies. They include studying within- and among-season movements of waterbirds on a spatial scale appropriate to both widely dispersing and more stationary species; multi-species censuses at multiple sites; further development and use of technology such as satellite transmitters and population-specific molecular markers; development of spatially explicit population models that consider within-season movements of waterbirds; and recognition from funding agencies that landscape-level issues cannot adequately be addressed without support for these types of studies.

Conservation Biology↗

USGS2014

Abdominally implanted satellite transmitters affect reproduction and survival rather than migration of large shorebirds

Satellite telemetry has become a common technique to investigate avian life-histories, but whether such tagging will affect fitness is a critical unknown. In this study, we evaluate multi-year effects of implanted transmitters on migratory timing and reproductive performance in shorebirds. Shorebirds increasingly are recognized as good models in ecology and evolution. That many of them are of conservation concern adds to the research responsibilities. In May 2009, we captured 56 female Black-tailed Godwits Limosa limosa limosa during late incubation in The Netherlands. Of these, 15 birds were equipped with 26-g satellite transmitters with a percutaneous antenna (7.8 % ± 0.2 SD of body mass), surgically implanted in the coelom. We compared immediate nest survival, timing of migration, subsequent nest site fidelity and reproductive behaviour including egg laying with those of the remaining birds, a comparison group of 41 females. We found no effects on immediate nest survival. Fledging success and subsequent southward and northward migration patterns of the implanted birds conformed to the expectations, and arrival time on the breeding grounds in 2010–2012 did not differ from the comparison group. Compared with the comparison group, in the year after implantation, implanted birds were equally faithful to the nest site and showed equal territorial behaviour, but a paucity of behaviours indicating nests or clutches. In the 3 years after implantation, the yearly apparent survival of implanted birds was 16 % points lower. Despite intense searching, we found only three eggs of two implanted birds; all were deformed. A similarly deformed egg was reported in a similarly implanted Whimbrel Numenius phaeopus returning to breed in central Alaska. The presence in the body cavity of an object slightly smaller than a normal egg may thus lead to egg malformation and, likely, reduced egg viability. That the use of implanted satellite transmitters in these large shorebirds reduced nesting propensity and might also lead to fertility losses argues against the use of implanted transmitters for studies on breeding biology, and for a careful evaluation of the methodology in studies of migration.

Friesl↗

USGS2012

Conservation implications when the nest predators are known

Conservation and management of passerines has largely focused on habitat manipulation or restoration because the natural communities on which these birds depend have been destroyed and fragmented. However, productivity is another important aspect of avian conservation, and nest predation can be a large source of nesting mortality for passerines. Recent studies using video surveillance to identify nest predators allow researchers to start evaluating what methods could be used to mitigate nest predation to help passerines of conservation concern. From recent studies, we identified latitudinal and habitat-related patterns in the importance of predator groups that depredate passerine nests. We then reviewed how knowledge of specific nest predators can benefit conservation of bird species of concern. Mammals were the dominant predator group in northern grasslands. Snakes were the dominant predator group in southern habitats. Fire ants were only a nest predator in southern latitudes. Differences in the importance of predator species or groups were likely the result of both their geographic patterns of distribution and habitat preferences. Some direct and indirect predator control measures developed for waterfowl management potentially could be used to benefit passerine productivity. We reviewed three examples-cowbirds, snakes in shrublands, and ground squirrels in grasslands-to illustrate how different predator control strategies may be needed in different situations. Mitigation of passerine nest predation will need to be based on knowledge of predator communities to be effective. This requires large samples of predation events with identified predators; video technology is essential for this task.

Studies in Avian Biology↗

USGS1981

Pharmocokinetics of cephalothin and cephalexin in selected avian species

Plasma concentrations and the biological half-lives of cephalothin and cephalexin in avian species of a variety of body sizes and metabolic rates were studied. The species chosen were eastern bobwhite quail (Colinus v virginianus), pigeons (Columba livia), hybrid rosybill ducks (Netta sp), greater sandhill cranes (Grus canadensis tabida), and emus (Dromiceius novaehollandiae). In the 1st phase of the study, cephalothin sodium was given IM in a dose of 100 mg/kg of body weight. Plasma concentrations reached peak (av 18 micrograms/ml) at 0.5 hour and were measurable 2.5 to 5.5 hours after drug administration. The biological half-life of cephalothin was 16 to 54 minutes; the half-life varied directly with increased species body weight, with the exception of the ducks studied. In the 2nd phase, cephalexin monohydrate was given orally in doses of 25, 35, and 50 mg/kg of body weight. Plasma concentrations reached peak (av 20 micrograms/ml) at 0.5 to 1 hour and were measurable 2.5 to 5.5 hours after drug administration. The biological half-life of cephalexin was 36 to 126 minutes. In the 3rd phase, differences in plasma concentrations and the half-lives of cephalexin between fed quail and fasted quail were insignificant. Dosage regimens for cephalothin of 100 mg/kg 4 times a day and for cephalexin of 35 to 50 mg/kg 4 times a day would be expected to establish and maintain therapeutic plasma concentrations in large birds (pigeons, cranes, and emus). These same doses, administered every 2 to 3 hours, would be expected to establish and maintain therapeutic plasma concentrations in smaller birds (quail, ducks).

American Journal of Veterinary Research↗

USGS2011

Rapid diagnosis of avian influenza virus in wild birds: Use of a portable rRT-PCR and freeze-dried reagents in the field

Wild birds have been implicated in the spread of highly pathogenic avian influenza (HPAI) of the H5N1 subtype, prompting surveillance along migratory flyways. Sampling of wild birds for avian influenza virus (AIV) is often conducted in remote regions, but results are often delayed because of the need to transport samples to a laboratory equipped for molecular testing. Real-time reverse transcriptase polymerase chain reaction (rRT-PCR) is a molecular technique that offers one of the most accurate and sensitive methods for diagnosis of AIV. The previously strict lab protocols needed for rRT-PCR are now being adapted for the field. Development of freeze-dried (lyophilized) reagents that do not require cold chain, with sensitivity at the level of wet reagents has brought on-site remote testing to a practical goal. Here we present a method for the rapid diagnosis of AIV in wild birds using an rRT-PCR unit (Ruggedized Advanced Pathogen Identification Device or RAPID, Idaho Technologies, Salt Lake City, UT) that employs lyophilized reagents (Influenza A Target 1 Taqman; ASAY-ASY-0109, Idaho Technologies). The reagents contain all of the necessary components for testing at appropriate concentrations in a single tube: primers, probes, enzymes, buffers and internal positive controls, eliminating errors associated with improper storage or handling of wet reagents. The portable unit performs a screen for Influenza A by targeting the matrix gene and yields results in 2-3 hours. Genetic subtyping is also possible with H5 and H7 primer sets that target the hemagglutinin gene. The system is suitable for use on cloacal and oropharyngeal samples collected from wild birds, as demonstrated here on the migratory shorebird species, the western sandpiper (Calidrus mauri) captured in Northern California. Animal handling followed protocols approved by the Animal Care and Use Committee of the U.S. Geological Survey Western Ecological Research Center and permits of the U.S. Geological Survey Bird Banding Laboratory. The primary advantage of this technique is to expedite diagnosis of wild birds, increasing the chances of containing an outbreak in a remote location. On-site diagnosis would also prove useful for identifying and studying infected individuals in wild populations. The opportunity to collect information on host biology (immunological and physiological response to infection) and spatial ecology (migratory performance of infected birds) will provide insights into the extent to which wild birds can act as vectors for AIV over long distances.

Journal of Visualized Experiments↗

USGS2022

The potential of semi-structured citizen science data as a supplement for conservation decision-making: Validating the performance of eBird against targeted avian monitoring efforts

Methods are being developed to capitalize on citizen science data for research and monitoring, but these data are rarely used within established decision-making frameworks of wildlife agencies. Citizen science data are often collected at higher resolution and extent than targeted monitoring programs, and may provide complementary information. Here, we demonstrate that carefully filtered semi-structured citizen science observations, when paired with targeted survey data, can produce ecological predictions at higher resolution and extent than targeted surveys alone, and both datasets can represent complementary aspects of species' ecology. We present case studies demonstrating how citizen science data can enhance or supplement decision-making of government and conservation organizations. First, we show how the continuous spatial coverage of citizen science projects, when coupled with targeted surveys, can improve estimates of metrics used by the U.S. Fish and Wildlife Service in regulatory processes to estimate population size, and inform take limits of federally managed species nationwide. Second, we show that the spatial coverage of citizen science accommodates dynamic avian space use patterns during key times of the year, relative to standardized monitoring protocols carried out by the Illinois Natural History Survey. Lastly, we demonstrate that citizen science information can replicate estimates of migratory chronologies for the Illinois Natural History Survey and the U.S. Fish and Wildlife Service for some waterfowl species, and in some contexts can supplement missing data on abundance. These findings illustrate the value of integrating validated information from semi-structured citizen science into the current evidence base used to justify, inform, and evaluate conservation decision-making.

California, Illinois, Iowa, Missouri↗

USGS2025

Laying sequence and oceanographic factors affect egg size in Scripps's Murrelets Synthliboramphus scrippsi at Santa Barbara Island

Egg size is an important avian life history parameter, with larger eggs indicating greater investment of resources in the chick. Prey availability can affect such investment. We investigated the effects of oceanographic conditions and laying sequence on Scripps's Murrelet Synthliboramphus scrippsi egg size at Santa Barbara Island, California during 2009-2017. We evaluated oceanographic covariates characterizing marine productivity for their effect on egg size, including large-scale oceanographic indices such as the Pacific Decadal Oscillation (PDO) index, Oceanic Niño Index (ONI), and North Pacific Gyre Oscillation (NPGO) index. We also evaluated a larval anchovy catch-per-unit-effort (ANCHL) index and the Biologically Effective Upwelling Transport Index (BEUTI) as region-wide indices, and sea surface temperature (SST) as a local index. We evaluated oceanographic conditions over the entire year and during the breeding season only. We also considered the contribution of lagged effects to oceanographic conditions. Our results generally ran counter to our hypothesis that increased ocean productivity should increase egg size. Based on Akaike's Information Criterion, the four top-ranked models provided support for an association between larger eggs and conditions indicative of lower oceanographic productivity, including lower values of BEUTI and NPGO, and higher values of ONI, PDO, and SST. The only result that supported our hypothesis was a positive relationship between ANCHL and egg size, although the 95% confidence interval for the effect included 0. The strongest relationship detected was between laying sequence and egg size, as second eggs were considerably larger than first eggs. Our results indicate substantial complexity in the relationship between ocean productivity and seabird demography. A better understanding of how ocean productivity affects seabird breeding outcomes through multiple mechanisms will help improve predictions of how seabirds will respond to changing ocean conditions.

California↗

USGS2014

Nutritional stress affects corticosterone deposition in feathers of Caspian tern chicks

Stressful environmental conditions affect the adrenocortical function of developing animals, which can have consequences for their fitness. Discovery of the avian stress hormone corticosterone (CORT) in feathers has the potential to broaden the application of endocrine research in ecological and evolutionary studies of wild birds by providing a long-term measure of CORT secretion. Mechanisms of CORT deposition in feathers are not well known and few studies have related feather CORT to circulating plasma CORT during feather growth. Our objective was to experimentally test the validity of using feather CORT as a measure of CORT secretion in developing birds experiencing nutritional stress. Caspian tern Hydroprogne caspia chicks were fed ad libitum or restricted (35% less than ad libitum) diets for four weeks. We measured CORT in feathers from these chicks to examine the relationship between feather CORT concentrations and nutritional limitation, circulating plasma CORT, and feather development. We found that feather CORT was higher in controls fed ad libitum than in restricted individuals, despite higher levels of plasma CORT in restricted chicks compared to controls. Feather mass and growth rates were strongly and positively related to feather CORT concentrations in both treatments. This is the first experimental study to show that feather CORT concentrations can be lower in response to nutritional stress, even when plasma CORT concentrations are elevated. Our results indicate that CORT deposition in feathers may be confounded when feather mass and growth rates are compromised by nutritional stress. We conclude that feather CORT can be used for assessing nutritional stress in growing birds, but the direction of response depends on how strongly stress affects feather development.

Journal of Avian Biology↗

USGS2017

The Partners in Flight handbook on species assessment Version 2017

Partners in Flight (PIF) is a cooperative venture of federal, state, provincial, and territorial agencies, industry, non-governmental organizations, researchers, and many others whose common goal is the conservation of North American birds (www.partnersinflight.org). While PIF has focused primarily on landbirds, it works in conjunction with other bird partners to promote coordinated conservation of all birds. PIF follows an iterative, adaptive planning approach that develops a sound scientific basis for decision-making and a logical process for setting, implementing, and evaluating conservation objectives (Pashley et al. 2000, Rich et al. 2004, Berlanga et al. 2010). The steps include: 1. Assessing conservation vulnerability of all bird species; 2. Identifying species most in need of conservation attention at continental and regional scales; 3. Setting of numerical population objectives for species of continental and regional importance; 4. Identifying conservation needs and recommended actions for species and habitats of importance; 5. Implementing strategies for meeting species and habitat objectives at continental and regional scales; 6. Evaluating success, making revisions, and setting new objectives for the future. The 2017 PIF Handbook on Species Assessment (2017 PIF Handbook) documents assessment rules and scores used in the Partners in Flight Landbird Conservation Plan: 2016 Revision for Canada and Continental United States (Rosenberg et al. 2016) and The State of North America’s Birds 2016 (NABCI 2016). It updates previous versions of the handbook (Panjabi et al. 2012, 2005, 2001) developed to accompany other PIF applications including Saving Our Shared Birds: Partners in Flight Tri-National Vision for Landbird Conservation (Berlanga et al. 2010) and the North American Landbird Conservation Plan (Rich et al. 2004). All current and past scores, data sources, and other related information are contained in databases hosted by the Bird Conservancy of the Rockies. Scores can be viewed online and downloaded as excel files, including archived versions (http://pif.birdconservancy.org/acad). The current accompanying Avian Conservation Assessment Database (ACAD) holds assessment scores and data for all 1585 native and 18 well-established non-native bird species found in mainland North America south to Panama plus adjacent islands and oceans. The taxonomy follows the American Ornithological Society’s 7th Edition Checklist of North and Middle American Birds, including updates though the 57th supplement, published in 2016 (http://checklist.aou.org/). The ACAD builds on archived PIF databases that hosted only data on the 882 landbirds native to Canada, USA and Mexico. This handbook is presented in two principal sections. Part I details the factors and scoring used by PIF to assess the vulnerability of species at continental and regional scales (i.e. step 1 of the planning approach above). Each assessment factor is based on biological criteria that evaluate distinct components of vulnerability throughout the life cycle of each species across its range. Part II describes the process of how the factors and the corresponding scores can be combined to highlight conservation needs (i.e. step 2 of the planning approach above). Both the scores and the process have evolved over time (Hunter et al. 1992, Carter et al. 2000, Panjabi et al. 2001, 2005, 2012) and continue to be updated in response to external review (Beissinger et al. 2000), broad partner expertise, and the emergence of new data and analytical tools.

Report↗

USGS2012

Hatching and fledging times from grassland passerine nests

1 day and was positively correlated with clutch size. Length of the fledging period for a brood was usually <1 day, and in nearly half the nests, fledging was completed within <2 hr. Video surveillance has proven to be a useful tool for providing new information and for corroborating published statements related to hatching and fledging chronology. Comparison of data collected from video and nest visits showed that carefully conducted nest visits generally can provide reliable data for deriving estimates of survival."}" data-sheets-userformat="{"2":8403202,"4":[null,2,16777215],"11":4,"14":[null,2,0],"15":"Inconsolata, monospace, arial, sans, sans-serif","16":11,"26":400}" data-sheets-formula="=VLOOKUP(R[0]C[-5],Fixed!R2C[-6]:C[-4],3,false)">Accurate estimates of fledging age are needed in field studies to avoid inducing premature fledging or missing the fledging event. Both may lead to misinterpretation of nest fate. Correctly assessing nest fate and length of the nestling period can be critical for accurate calculation of nest survival rates. For researchers who mark nestlings, knowing the age at which their activities may cause young to leave nests prematurely could prevent introducing bias to their studies. We obtained estimates of fledging age using data from grassland bird nests monitored from hatching through fledging with video-surveillance systems in North Dakota and Minnesota during 1996–2001. We compared these values to those obtained from traditional nest visits and from available literature. Mean and modal fledging ages for video-monitored nests were generally similar to those for visited nests, although Clay-colored Sparrows (Spizella pallida) typically fledged 1 day earlier from visited nests. Average fledging ages from both video and nest visits occurred within ranges reported in the literature, but expanded by 1–2 days the upper age limit for Clay-colored Sparrows and the lower age limit for Bobolinks (Dolichonyx oryzivorus). Video showed that eggs hatched throughout the day whereas most young fledged in the morning (06:30–12:30 CDT). Length of the hatching period for a clutch was usually >1 day and was positively correlated with clutch size. Length of the fledging period for a brood was usually <1 day, and in nearly half the nests, fledging was completed within <2 hr. Video surveillance has proven to be a useful tool for providing new information and for corroborating published statements related to hatching and fledging chronology. Comparison of data collected from video and nest visits showed that carefully conducted nest visits generally can provide reliable data for deriving estimates of survival.

Studies in Avian Biology↗

USGS2010

Geographic variation in the plumage coloration of willow flycatchers Empidonax traillii

The ability to identify distinct taxonomic groups of birds (species, subspecies, geographic races) can advance ecological research efforts by determining connectivity between the non-breeding and breeding grounds for migrant species, identifying the origin of migrants, and helping to refine boundaries between subspecies or geographic races. Multiple methods are available to identify taxonomic groups (e.g., morphology, genetics), and one that has played an important role for avian taxonomists over the years is plumage coloration. With the advent of electronic devices that can quickly and accurately quantify plumage coloration, the potential of using coloration as an identifier for distinct taxonomic groups, even when differences are subtle, becomes possible. In this study, we evaluated the degree to which plumage coloration differs among the four subspecies of the willow flycatcher Empidonax traillii, evaluated sources of variation, and considered the utility of plumage coloration to assign subspecies membership for individuals of unknown origin. We used a colorimeter to measure plumage coloration of 374 adult willow flycatchers from 29 locations across their breeding range in 2004 and 2005. We found strong statistical differences among the mean plumage coloration values of the four subspecies; however, while individuals tended to group around their respective subspecies' mean color value, the dispersion of individuals around such means overlapped. Mean color values for each breeding site of the three western subspecies clustered together, but the eastern subspecies' color values were dispersed among the other subspecies, rather than distinctly clustered. Additionally, sites along boundaries showed evidence of intergradation and intermediate coloration patterns. We evaluated the predictive power of colorimeter measurements on flycatchers by constructing a canonical discriminant model to predict subspecies origin of migrants passing through the southwestern U.S. Considering only western subspecies, we found that individuals can be assigned with reasonable certainty. Applying the model to migrants sampled along the Colorado River in Mexico and the U.S. suggests different migration patterns for the three western subspecies. We believe that the use of plumage coloration, as measured by electronic devices, can provide a powerful tool to look at ecological questions in a wide range of avian species.

Journal of Avian Biology↗

USGS2015

The effects of heterospecifics and climatic conditions on incubation behavior within a mixed-species colony

Parental incubation behavior largely influences nest survival, a critical demographic process in avian population dynamics, and behaviors vary across species with different life history breeding strategies. Although research has identified nest survival advantages of mixing colonies, behavioral mechanisms that might explain these effects is largely lacking. We examined parental incubation behavior using video-monitoring techniques on Alcatraz Island, California, of black-crowned night-heron Nycticorax nycticorax (hereinafter, night-heron) in a mixed-species colony with California gulls Larus californicus and western gulls L. occidentalis . We first quantified general nesting behaviors (i.e. incubation constancy, and nest attendance), and a suite of specific nesting behaviors (i.e. inactivity, vigilance, preening, and nest maintenance) with respect to six different daily time periods. We employed linear mixed effects models to investigate environmental and temporal factors as sources of variation in incubation constancy and nest attendance using 211 nest days across three nesting seasons (2010–2012). We found incubation constancy (percent of time on the eggs) and nest attendance (percent of time at the nest) were lower for nests that were located < 3 m from one or more gull nest, which indirectly supports the predator protection hypothesis, whereby heterospecifics provide protection allowing more time for foraging and other self-maintenance activities. To our knowledge, this is the first empirical evidence of the influence of one nesting species on the incubation behavior of another. We also identified distinct differences between incubation constancy and nest attentiveness, indicating that these biparental incubating species do not share similar energetic constraints as those that are observed for uniparental species. Additionally, we found that variation in incubation behavior was a function of temperature and precipitation, where the strength of these effects was dependent on the time of day. Overall, these findings strengthen our understanding of incubation behavior and nest ecology of a colonial-nesting species.

California↗

USGS2023

Selenium hazards in the Salton Sea environment—Summary of current knowledge to inform future wetland management

Quaternary marine and continental shales in the western United States are sources of selenium that can be loaded into the aquatic environment through mining, agricultural, and energy production processes. The mobilization of selenium from shales through agricultural irrigation has been recognized since the 1930s; however, discovery of deformities in birds and other wildlife using agricultural habitats during the 1980s spurred studies to determine the extent and effects of the contamination. Through these early studies, researchers determined that biota in the Salton Sea drainage basin was at risk from legacy selenium contamination in the Colorado River watershed. The Salton Sea and its surrounding managed and unmanaged wetlands provide vital inland habitat and trophic support for diverse assemblages of resident and migratory wildlife, and understanding regional selenium hazards for these trust species is a priority for many Federal and State agencies. The modern Salton Sea is a shallow, landlocked saline lake in Riverside and Imperial Counties (not shown) of California that is sustained by irrigation return and perennial river inflow. Changes in water transfer agreements under the 2003 Quantification Settlement Agreement (QSA) have resulted in reduced irrigation flow, declining lake levels, and the evolution of unmanaged wetlands in areas where drains and rivers no longer reach the Salton Sea. These wetlands provide additional habitat for some species of concern, but their potential to increase selenium hazards for trust species is largely unknown. From the 1980s to 2020, efforts to document selenium contamination and effects throughout the region have resulted in a considerable amount of selenium data from the Salton Sea and its surrounding drainage basin; however, no long-term (greater than 20 years), consistent sampling program has been established, and all data have been collected by different entities using a variety of protocols and analytical techniques. This lack of coordination has been previously documented in regional management plans and has led to difficulty in reliably assessing selenium hazards in the Salton Sea environment. This report provides a summary of the available disparate selenium information collected from water, sediment, and biota in the Salton Sea region since the 1980s and to identify data gaps that need to be filled to understand the potential effects of selenium on species of concern, including federally endangered desert pupfish ( Cyprinodon macularius ) and Yuma Ridgway’s Rail ( Rallus obsoletus yumanensis; formerly Yuma Clapper Rail, Rallus longirostris yumanensis ). Available data from the Salton Sea drainage basin show that water from the Colorado River has the lowest selenium concentration of all surface water sources. All other surface water flowing into the Salton Sea has elevated selenium concentrations due to evaporation and evapotranspiration that occurs in agricultural fields and associated water delivery infrastructure or leaching of selenium from irrigated farmland soils. The Salton Sea has lower selenium concentrations because of various biogeochemical processes that recycle selenium into the sediment or volatilize it to the atmosphere; however, these mechanisms are not well defined, and it is not clear if selenium cycling will change in response to possible changes in the oxidation state of the Salton Sea bottom waters as water levels decline. Agricultural drains have the highest average selenium concentrations, but few drains have been sampled since changes in irrigation practices have occurred (due to the 2003 QSA). Groundwater selenium concentrations are variable; some wells south of the Salton Sea have selenium concentrations as high as 300 micrograms per liter (µg/L), whereas selenium concentrations are below detection in other wells. Groundwater and surface-water geothermal discharge zones around the margins of the Salton Sea and in unmanaged wetlands have not been studied in detail, and published selenium measurements are not available for these surface features. Selenium concentrations in the sediment of the Salton Sea drainage basin are highest in wetland particulate organic matter and the Salton Sea lakebed, indicating that removal of selenium from the water to the sediment has been a primary mechanism for keeping selenium concentrations low in the water column. Sediment selenium concentrations in wetlands are lower than in the Salton Sea but higher than inflowing drains and rivers, indicating the lentic wetland sites also may be important sinks for selenium because of biogeochemical processes. Sediment selenium data have not been collected in agricultural drains since changes in irrigation practices occurred (due to the 2003 QSA), and it is unknown if selenium sequestration from the water column has changed in these systems. We divided biological data into broad taxonomic categories, including primary producers, invertebrates, herpetofauna, mammals, fishes, and birds to facilitate evaluation of selenium concentrations and spatiotemporal trends observed in the Salton Sea. Overall, selenium concentrations were substantially greater in algae samples compared to all vascular plant samples combined. Median selenium concentrations in several invertebrate taxa (Chironomidae, Formicidae, Corixidae, Corbiculidae and Nereididae, and Decapoda) exceeded the maximum suggested dietary threshold of 3.0–4.0 micrograms per gram (µg/g) dry weight (dw) for predators consuming invertebrates in aquatic food webs. The greatest number of samples were collected from fish, and selenium distributions among species and locations showed that the range for most samples was lower than the U.S. Environmental Protection Agency selenium criterion for aquatic life (8.5 µg/g dw whole body, 11.3 µg/g dw fillets). The median selenium concentrations for whole body fish were below the selenium criterion in most locations, except for bairdiella ( Bairdiella icistia ) from the Salton Sea and irrigation drains, a few individual tilapia spp. (family Cichlidae, including genera Tilapia, Oreochromis , and their hybrids) from the river and river outlets, and several western mosquitofish ( Gambusia affinis ) and sailfin molly ( Poecilia latipinna ) from irrigation drain outlets. For avian samples combined among years and locations, median selenium concentrations in livers from all families except waders and Ibis (family Threskiornithidae) were higher than levels expected to cause selenium toxicosis (10–20 µg/g dw), and all median egg concentrations were above or near 6.0 μg/g dw, which is a conservative threshold value for reproductive impairment. Most knowledge gaps we identified for water, sediment, and biota were interrelated, and the use of integrated approaches to address knowledge gaps can provide greater insight into the drivers behind selenium hazards. Integrated water, sediment, and biota studies could help identify cost-effective management solutions that serve multiple purposes. A comprehensive analysis of the hydrology, biogeochemistry, and food-web processes in wetlands and other habitats can inform predictive models to identify drivers of selenium bioavailability, uptake from the environment and subsequent trophic transfer, ultimately forming the basis for experimental habitat management manipulations to minimize selenium hazards to wildlife. Furthermore, a comprehensive, long-term sampling and analytical laboratory plan would enable comparison of data among different entities that are sampling at the Salton Sea. Such efforts are well suited to help fill knowledge gaps that preclude understanding of selenium hazards and future management options for biota using Salton Sea habitats, including newly formed wetlands throughout the region. All data compiled for this report are available in two U.S. Geological Survey data releases: Groover and others (2022) for water and sediment samples and De La Cruz and others (2022) for biological samples. The data releases include all publicly available data for selenium concentrations in water, sediment, and biological samples collected in and around the Salton Sea, including the Coachella and Imperial Valleys. The data releases also include previously unpublished data.

California↗