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USGS1999

Nest-site selection in the acorn woodpecker

Acorn Woodpeckers ( Melanerpes formicivorus ) at Hastings Reservation in central California prefer to nest in dead limbs in large, dead valley oaks ( Quercus lobata ) and California sycamores ( Platanus racemosa ) that are also frequently used as acorn storage trees. Based on 232 nest cavities used over an 18-year period, we tested whether preferred or modal nest-site characters were associated with increased reproductive success (the "nest-site quality" hypothesis). We also examined whether more successful nests were likely to experience more favorable microclimatic conditions or to be less accessible to terrestrial predators. We found only equivocal support for the nest-site quality hypothesis: only 1 of 5 preferred characters and 2 of 10 characters exhibiting a clear modality were correlated with higher reproductive success. All three characteristics of nests known or likely to be associated with a more favorable microclimate, and two of five characteristics likely to render nests less accessible to predators, were correlated with higher reproductive success. These results suggest that nest cavities in this population are built in part to take advantage of favorable microclimatic conditions and, to a lesser extent, to reduce access to predators. However, despite benefits of particular nest characteristics, birds frequently nested in apparently suboptimal cavities. We also found a significant relationship between mean group size and the history of occupancy of particular territories and the probability of nest cavities being built in microclimatically favorable live limbs, suggesting that larger groups residing on more stable territories were better able to construct nests with optimal characteristics. This indicates that there may be demographic, as well as ecological, constraints on nest-site selection in this primary cavity nester.

The Auk↗

USGS1987

Selenium in aquatic organisms from subsurface agricultural drainage water, San Joaquin Valley, California

Concentrations of total selenium were high in 1983 in water, sediment, organic detritus, aquatic plants and invertebrates, and mosquitofish ( Gambusia affinis ) from Kesterson Reservoir (San Joaquin Valley, California) and the San Luis Drain. Selenium concentrations in biota from the Reservoir and Drain (referred to here collectively as “Kesterson”) exceeded 300 (μg/g dry weight in some samples of algae, submerged rooted plants, chironomids, and mosquitofish, and were as high as 440 μg/g dry weight in decomposing detritus. Overall, selenium concentrations in samples from Kesterson averaged about 100-fold higher than those from the Volta Wildlife Area (here termed “Volta”), a nearby site that does not receive subsurface drainage water. Selenium concentrations generally increased from water to sediment to plants to animals. Spatial (geographic) patterns were observed for selenium concentrations in samples from Kesterson, but not in those from Volta. Higher concentrations were usually measured in samples from the San Luis Drain than from the evaporation ponds that comprise Kesterson Reservoir. At Kesterson, concentrations were usually higher in August than in May. The elevated levels of selenium measured in forage organisms from Kesterson are probably toxic to sensitive consumer animals, and may explain recent observations of dead and deformed embryos in eggs of aquatic birds that nest at the Reservoir. The effects of the selenium on fish living in subsurface agricultural drainage water are still poorly understood.

California↗

USGS2006

Forecasting selenium discharges to the San Francisco Bay-Delta Estuary: Ecological effects of a proposed San Luis Drain extension

Selenium discharges to the San Francisco Bay-Delta Estuary (Bay-Delta) could change significantly if federal and state agencies (1) approve an extension of the San Luis Drain to convey agricultural drainage from the western San Joaquin Valley to the North Bay (Suisun Bay, Carquinez Strait, and San Pablo Bay); (2) allow changes in flow patterns of the lower San Joaquin River and Bay-Delta while using an existing portion of the San Luis Drain to convey agricultural drainage to a tributary of the San Joaquin River; or (3) revise selenium criteria for the protection of aquatic life or issue criteria for the protection of wildlife. Understanding the biotransfer of selenium is essential to evaluating effects of selenium on Bay-Delta ecosystems. Confusion about selenium threats to fish and wildlife stem from (1) monitoring programs that do not address specific protocols necessary for an element that bioaccumulates; and (2) failure to consider the full complexity of the processes that result in selenium toxicity. Past studies show that predators are more at risk from selenium contamination than their prey, making it difficult to use traditional methods to predict risk from environmental concentrations alone. This report presents an approach to conceptualize and model the fate and effects of selenium under various load scenarios from the San Joaquin Valley. For each potential load, progressive forecasts show resulting (1) water-column concentration; (2) speciation; (3) transformation to particulate form; (4) particulate concentration; (5) bioaccumulation by invertebrates; (6) trophic transfer to predators; and (7) effects on those predators. Enough is known to establish a first-order understanding of relevant conditions, biological response, and ecological risks should selenium be discharged directly into the North Bay through a conveyance such as a proposed extension of the San Luis Drain. The approach presented here, the Bay-Delta selenium model, determines the mass, fate, and effects of selenium released to the Bay-Delta through use of (1) historical land-use, drainage, alluvial-fill, and runoff databases; (2) existing knowledge concerning biogeochemical reactions and physiological parameters of selenium (e.g., speciation, partitioning between dissolved and particulate forms, and bivalve assimilation efficiency); and (3) site-specific data mainly from 1986 to 1996 for clams and bottom-feeding fish and birds. Selenium load scenarios consider effluents from North Bay oil refineries and discharges of agricultural drainage from the San Joaquin Valley to enable calculation of (a) a composite freshwater endmember selenium concentration at the head of the estuary; and (b) a selenium concentration at a selected seawater location (Carquinez Strait) as a foundation for modeling. Analysis of selenium effects also takes into account the mode of conveyance for agricultural drainage (i.e., the San Luis Drain or San Joaquin River); and flows of the Sacramento River and San Joaquin River on a seasonal or monthly basis. Load scenarios for San Joaquin Valley mirror predictions made since 1955 of a worsening salt (and by inference, selenium) build-up exacerbated by an arid climate and massive irrigation. The reservoir of selenium in the San Joaquin Valley is sufficient to provide loading at an annual rate of approximately 42,500 pounds of selenium to a Bay-Delta disposal point for 63 to 304 years at the lower range of projections presented here, even if influx of selenium from the California Coast Ranges could be curtailed. Disposal of wastewaters on an annual basis outside of the San Joaquin Valley may slow the degradation of valley resources, but drainage alone cannot alleviate the salt and selenium build-up in the San Joaquin Valley, at least within a century. Load scenarios also show the different proportions of selenium loading to the Bay-Delta. Oil refinery loads from 1986 to 1992 ranged from 8.5 to 20 pounds of selenium per day; with treatment and cleanup, loads decreased to 3.0 pounds of selenium per day in 1999. In contrast, San Joaquin Valley agricultural drainage loads disposed of in a San Luis Drain extension could range from 45 to 117 pounds of selenium per day across a set of historical and future conditions. Components of this valley-wide load include five source subareas (i.e., Grassland, Westlands, Tulare, Kern, and Northern) defined by water and drainage management. Loads vary per subarea mainly because of proximity of the subarea to geologic sources of selenium and irrigation history. Loads from the Sacramento River, depending on flow conditions, range from 0.8 to 10 pounds of selenium per day. Loads from the San Joaquin River vary depending on restoration and flow conditions, which are considered. A consistent picture of ecological risk emerges under modeled selenium discharges from a proposed San Luis Drain extension. The threat to the estuary is greatest during low flow seasons and critically dry years. Where selenium undergoes reactions typical of low flow or longer residence time, highly problematic bioaccumulation in prey (food) is forecast. Surf scoter, greater and lesser scaup, and white sturgeon appear to be most at risk because these Bay-Delta predators feed on deposit and filter-feeding bivalves. Recent findings add Sacramento splittail and Dungeness crab to that list. During the low flow season of critically dry years, forecasted selenium concentrations in water, particulate matter, prey (diet), and predator tissue exceed guidelines with a high certainty of producing adverse effects under the most likely load scenario from a proposed San Luis Drain extension. High flows afford some protection under certain conditions in modeled San Joaquin River scenarios. However, meeting a combined goal of releasing a specific load during maximum flows and keeping selenium concentrations in the river below a certain objective to protect against bioaccumulation may not always be attainable. Management of the San Joaquin River on a constant concentration basis also could create problematic bioaccumulation during a wet year, especially during the low flow season, because high flows translate to high loads that are not always offset by seasonal river inflows. Prior to refinery cleanup, selenium contamination was sufficient to threaten reproduction in key species within the Bay-Delta ecosystems and human health advisories were posted based on selenium concentrations in tissues of diving ducks. During this time, selenium concentrations in the Bay-Delta were well below the most stringent recommended water quality criterion [1 microgram per liter (1 µg/L)]. Enhanced biogeochemical transformations to bioavailable particulate selenium and efficient bioaccumulation by bivalves characterized the system. If these biogeochemical conditions continue to prevail and agricultural selenium sources replace or exceed refinery sources, ecological forecasts suggest the risk of adverse effects will be difficult to eliminate under an out-of-valley resolution to the selenium problem. The Bay-Delta selenium model presented here is a systematic approach for conducting forecasts of the ecological effects from selenium on aquatic food webs. It is a new tool that links and models the major processes leading from loads through consumer organisms to predators. It also is a feasible approach for site-specific analysis and could provide a framework for developing new protective selenium foodweb guidelines and predator criteria. Model components that help ensure understanding ecosystems and the basis of environmental protection are (1) contaminant concentrations and speciation in sources, such as particulate material, that most influence bioavailability; (2) bioaccumulation models that calculate concentrations in diet, specifically in bivalves of the Bay-Delta that act as sensitive indicators of selenium contamination; (3) food-web type that determines what animals are threatened and when; and (4) multiple media concentrations (water, particulate material, and tissue of prey and predators) that, in-combination, determine risk or hazard.

California↗

USGS2015

Golden Eagle mortality at a utility-scale wind energy facility near Palm Springs, California

Golden Eagle ( Aquila chrysaetos ) mortality associated with wind energy turbines and infrastructure is under-reported and weakly substantiated in the published literature. I report two cases of mortality at a utility-scale renewable energy facility near Palm Springs, California. The facility has been in operation since 1984 and included 460 65KW turbines mounted on 24.4 m or 42.7 m lattice-style towers with 8 m rotor diameters. One mortality event involved a juvenile eagle that was struck and killed by a spinning turbine blade on 31 August, 1995. The tower was 24.4 m high. The other involved an immature female that was struck by a spinning blade on another 24.4 m tower on 17 April, 1997 and was later euthanized due to the extent of internal injuries. Other raptor mortalities incidentally observed at the site, and likely attributable to turbines, included three Red-tailed Hawks ( Buteo jamaicensis ) found near turbines.

California↗

USGS2023

Demographics and gross pathology of scoters and scaups killed by the Cosco Busan oil spill in California

Unusual wildlife mortality events provide a unique opportunity to collect information on demographics, disease, and body condition in affected wildlife, which may be useful for informing oil spill damage assessments and future spill responses. In November 2007, the Cosco Busan Oil Spill occurred in San Francisco Bay, California, a globally important wintering area for waterfowl. The spill resulted in the mortality of scoters Melanitta spp. and scaups Aythya spp., species that have declined significantly over recent decades. We examined the demography (sex and age ratios) and prevalence of grossly apparent disease (acanthocephalan parasite infection and mycotic disease) in 288 Surf Scoters M. perspicillata , White-winged Scoters M. deglandi , Greater Scaup A. marila , and Lesser Scaup A. affinis killed in the oil spill. The proportions of females and juveniles in examined Surf Scoters was unexpectedly high (0.98:1, females:males, 0.73:1 juveniles:adults) for this species with normally strong male- and adult-biased populations. This disproportionate mortality of female Surf Scoters could result in a greater population impact on this female-limited species, suggesting a mechanism for steep declines in San Francisco Bay scoter numbers in the years after the Cosco Busan oil spill. Significantly greater rates of acanthocephalan infection in juvenile vs. adult Surf Scoters indicated a possible interaction between acanthocephalan parasitism and juvenile-biased mortality in our sample. Birds that died during rehabilitation had significantly greater rates of mycotic disease (10% infected) than birds found dead in the field (3%), indicating that infections began or worsened during rehabilitation. Greater Scaup had proportionally greater rates of infection with mycotic disease (26% of individuals) than other species, indicating that they may be particularly susceptible to the disease. We encourage the documentation of demographics and disease as a regular part of future responses to oil spills, or other mortality events, to gain insight into population impacts and improve rehabilitation efforts of affected populations.

California↗

USGS1985

Determining age and sex of American coots

Reliable techniques for age and sex determination of migrating and wintering American Coots ( Fulica americana ) have not been available. Breeding coots can be ages through age 3 by tarsal color (birds 4 years and older were placed in a 4+ age class) (Crawford 1978), and males and females have sex-specific behaviors and calls while on breeding territories (Gullion 1950, 1952). Externally, juvenile coots differ from adults in having gray (as opposed to white) bills and brown (as opposed to red) eyes to an age of 75 days (Gullion 1954-394). Bill color changes to white by about 120 days. No quantitative data have been available, however, on the proportion of juveniles retaining these traits throughout fall and early winter. Nonbreeding coots can be ages as juvenile or adult by internal examination of the thickness of the wall of the bursa of Fabricius, although bursal depth does not predictably decline with age (Fredrickson 1968). Attempts to sex coots by single external measurements of combinations of measurements have met with mixed success. Eight-five percent of 101 fall migrants in Wisconsin could be sexed by the length of the metatarsus-midtoe including claw by using 139.5 mm as a cutoff point (Burton 1959), whereas 88% of 67 coots in California were correctly sexed by the length of the metatarsus-midtoe without claw using 127.5 mm as the cutoff point (Gullion 1952). Two-hundred-thirty-two of 291 coots collected in Iowa, however, were in the zone of overlap between the sexes for this measurement (Fredrickson 1968). Previous studies attempting to develop aging and sexing techniques for American Coots have been limited to a few study sites or to 1 season or year, often failing to take geographical, annual, and seasonal morphological variation into account (e.g., Visser 1976, Fjeldsa 1977). We designed the present study to refine and quantify external and internal age and sex criteria for postbreeding coots, with the objective of defining techniques applicable for all seasons over a wide geographical area.

Journal of Field Ornithology↗

USGS2025

Sex differences in migration routes and non-breeding areas of a declining shorebird

Migratory birds face different threats and pressures across their annual cycle, and understanding the impact of these factors on individuals is critical to the conservation of avian populations. Individuals from the same breeding population may share the same non-breeding areas, and thus experience similar conditions, or they may travel to different habitats or regions during migration and the stationary non-breeding period. Marbled Godwits ( Limosa fedoa ) breeding in the Northern Great Plains, which have experienced steep population declines, are thought to spend the non-breeding period primarily on the Pacific Coast of the United States and Mexico. However, little is known about migratory routes, stopover sites, and non-breeding locations of specific breeding populations, nor whether individuals from the same breeding population remain together throughout the year. We deployed satellite transmitters on four mated pairs of godwits breeding in southern Alberta, Canada, with individuals tracked over a mean of 2.2 annual cycles (range 0.6–5.6, excluding one unit that stopped transmitting immediately following deployment). Counter to our expectations, females and males separated completely following breeding, with females traveling to non-breeding areas along the coast of California, United States, and males stopping over at Great Salt Lake, Utah, United States, and spending the non-breeding period in Baja California Sur, Mexico, a distance of ~1300 km from their mates. Despite spending nine months apart, individuals from this breeding population have previously been shown to have high mate fidelity. Interestingly, individuals mostly used protected areas during the non-breeding period, in contrast to the human-modified agricultural landscapes that make up the majority of their breeding grounds. Despite a small sample size, our results suggest a strong pattern of differential migration based on sex, with implications for the specific environmental conditions, and potentially threats, faced by female and male godwits across the annual cycle.

Avian Conservation and Ecology↗

USGS2012

A synthesis of aquatic science for management of Lakes Mead and Mohave

Lakes Mead and Mohave, which are the centerpieces of Lake Mead National Recreation Area, provide many significant benefits that have made the modern development of the Southwestern United States possible. Lake Mead is the largest reservoir by volume in the nation and it supplies critical storage of water supplies for more than 25 million people in three Western States (California, Arizona, and Nevada). Storage within Lake Mead supplies drinking water and the hydropower to provide electricity for major cities including Las Vegas, Phoenix, Los Angeles, Tucson, and San Diego, and irrigation of more than 2.5 million acres of croplands. Lake Mead is arguably the most important reservoir in the nation because of its size and the services it delivers to the Western United States. This Circular includes seven chapters. Chapter 1 provides a short summary of the overall findings and management implications for Lakes Mead and Mohave that can be used to guide the reader through the rest of the Circular. Chapter 2 introduces the environmental setting and characteristics of Lakes Mead and Mohave and provides a brief management context of the lakes within the Colorado River system as well as overviews of the geological bedrock and sediment accumulations of the lakes. Chapter 3 contains summaries of the operational and hydrologic characteristics of Lakes Mead and Mohave. Chapter 4 provides information on water quality, including discussion on the monitoring of contaminants and sediments within the reservoirs. Chapter 5 describes aquatic biota and wildlife, including food-web dynamics, plankton, invertebrates, fish, aquatic birds, and aquatic vegetation. Chapter 6 outlines threats and stressors to the health of Lake Mead aquatic ecosystems that include a range of environmental contaminants, invasive species, and climate change. Chapter 7 provides a more detailed summary of overall findings that are presented in Chapter 1; and it contains a more detailed discussion on associated management implications, additional research, and monitoring needs.

Arizona, Nevada↗

USGS2021

Informing wetland management with waterfowl movement and sanctuary use responses to human-induced disturbance

Long-term environmental management to prevent waterfowl population declines is informed by ecology, movement behavior and habitat use patterns. Extrinsic factors, such as human-induced disturbance, can cause behavioral changes which may influence movement and resource needs, driving variation that affects management efficacy. To better understand the relationship between human-based disturbance and animal movement and habitat use, and their potential effects on management, we GPS tracked 15 dabbling ducks in California over ~4-weeks before, during and after the start of a recreational hunting season in October/November 2018. We recorded locations at 2-min intervals across three separate 24-h tracking phases: Phase 1) two weeks before the start of the hunting season (control (undisturbed) movement); Phase 2) the hunting season opening weekend; and Phase 3) a hunting weekend two weeks after opening weekend. We used GLMM models to analyze variation in movement and habitat use under hunting pressure compared with ‘normal’ observed patterns prior to commencement of hunting. We also compared responses to differing levels of disturbance related to the time of day (high - shooting/~daytime); moderate - non-lethal (~crepuscular); and low - night). During opening weekend flight (% time and distance) more than doubled during moderate and low disturbance and increased by ~50% during high disturbance compared with the pre-season weekend. Sanctuary use tripled during moderate and low disturbance and increased ~50% during high disturbance. Two weeks later flight decreased in all disturbance levels but was only less than the pre-season levels during high disturbance. In contrast, sanctuary use only decreased at night, although not to pre-season levels, while daytime doubled from ~45% to >80%. Birds adjust rapidly to disturbance and our results have implications for energetics models that estimate population food requirements. Management would benefit from reassessing the juxtaposition of essential sanctuary and feeding habitats to optimize wetland management for waterfowl.

Journal of Environmental Management↗

USGS2020

Transmitter effects on growth and survival of Forster’s tern chicks

Radio‐telemetry is a commonly used scientific technique that allows researchers to collect detailed movement, habitat use, and survival data of animals; however, evidence indicates that using telemetry can affect behavior and survival. Using multiple breeding colonies and years, we investigated the effects of attached radio‐transmitters on growth and survival of Forster's tern ( Sterna forsteri ) chicks in San Francisco Bay, California, USA, 2010–2011. We tested these potential effects at isolated islands that allowed for high re‐capture rates (typically >85%) in radio‐marked and banded‐only chicks. Modeled Gompertz growth curves suggested that transmitters had a small negative effect on some of the asymptotic growth parameters of tern chicks; tarsus (−1.5 ± 0.7% [SE]), culmen (−1.7 ± 1.2%), and wing (−4.9 ± 2.0%) lengths were shorter for radio‐marked chicks compared to banded‐only chicks. In contrast, there was no difference in asymptotic mass between radio‐marked chicks and banded‐only chicks. Survival from hatching to fledging was lower for radio‐marked chicks than banded‐only chicks during 2010 (banded‐only = 0.313 ± 0.162 vs. radio‐marked = 0.250 ± 0.165) and 2011 (0.193 ± 0.030 vs. 0.123 ± 0.027). Most of the transmitter effect occurred within the first week after hatching, rather than in older chicks. Notably, the effect of transmitters on chick survival was primarily additive, indicating that the effect of transmitters on radio‐marked chicks was not influenced by other ecological covariates. Given the effect radio‐transmitters had on survival did not change across temporal or ecological gradients, transmitters can still be used to evaluate ecological factors affecting survival and timing of mortality and radio‐marked birds can be used to make inferences to the general population.

California↗

USGS2023

Insectivorous bat foraging tracks the availability of aquatic flies (Diptera)

Rivers and their adjacent riparian zones are model ecosystems for observing cross-ecosystem energy transfers. Aquatic insects emerging from streams, for example, are resource subsidies that support riparian consumers such as birds, spiders, lizards, and bats. We collaborated with recreational river runners in Grand Canyon, Arizona, USA, to record acoustic bat activity and sample riparian insects using light traps at dusk from April through October 2017–2020. River runners collected these data on 1,428 events over 611 sampling nights at 410 sites throughout a 470-km segment of the Colorado River. We documented 71 insect taxa in light traps and recorded 19 bat species with acoustic detectors. We hypothesized that bat activity along this highly regulated river segment would be influenced primarily by variation in prey availability, as compared to other habitat descriptors. We predicted that bat activity would be positively related to aquatic insect catch rates and unrelated to terrestrial insect abundance. We fit Bayesian regression models to test these hypotheses and to quantify the relationship between bat activity and a suite of environmental variables: time of year, time of day, distance from perennial tributaries, distance from rapids, channel width, geomorphic reach, tall vegetation cover, air temperature, and lunar phase. Bat activity was positively related to the abundance of aquatic flies (Diptera), which outcompeted all other prey categories and structural habitat descriptors in our models. Within our dusk sampling period, activity of small myotis (California myotis [ Myotis californicus ] and Yuma myotis [ M. yumanensis ]) was high late in the evening and canyon bats ( Parastrellus hesperus ), conversely, were more active early in the evening. Activity of canyon bats varied seasonally, with peak activity in August. Our results support the hypothesis that aquatic prey, specifically aquatic flies, are key predictors of bat activity along a large, regulated river corridor and demonstrate the power of community science as a tool for ecosystem monitoring.

Journal of Wildlife Management↗

USGS2003

Chromium geochemistry of serpentinous sediment in the Willow core, Santa Clara County, California

A preliminary investigation of Cr geochemistry in serpentinous sediment completed for a multiple-aquifer ground-water monitoring well (Willow core of Santa Clara County, CA) determined sediment at depths >225 meters contains Cr concentrations ranging from 195 to 1155 mg/kg. Serpentinous sediment from this site is a potential source of non-anthropogenic Cr contamination. Chromium-bearing minerals such as Cr-spinel appear to be the main source of Cr in the sediment; however, Cr-bearing silicates and clay minerals are additional Cr sources. Aqueous Cr concentrations in the sediment are <4.6 mg/L; however, the valence of Cr was not identified in the solutions or in the sediment. Although there is no indication of Cr(VI) contamination derived from the serpentinous sediment, elevated Cr concentrations in the sediment, the observed ‘dissolution’ textures of the Cr-bearing minerals, the estimated redox environment, and water chemistry indicate the formation of Cr(VI) is potentially favorable.

California↗

USGS2002

Use of restored riparian habitat by the endangered least Bell's vireo (Vireo bellii pusillus)

A primary objective of riparian restoration in California is the creation of habitat for endangered species. Four restoration sites in San Diego County were monitored between 1989 and 1993 and evaluated for their suitability as nesting habitat for Vireo bellii pusillus (Least Bell's Vireo), a state and federally endangered obligate riparian breeder. Vegetation structure at each site was quantified annually and compared to a model of canopy architecture derived from Least Bell's Vireo territories in natural habitat. Vireo use of restored habitat was documented through systematic surveys and nest monitoring. By 1993, only one site in its entirety met the habitat suitability criteria of the model, but portions of each site during all years did so. Differences between sites in the time required to develop suitable habitat—well-developed layered vegetation from the ground to under 8m in height)—were attributable largely to variation in annual rainfall. Vireos visited restoration sites to forage as early as the first growing season, but they did not establish territories or nest there until at least part of the site supported suitable habitat as determined from the model. Placement of territories and nests coincided with patches of dense vegetation characteristic of natural nesting areas. Occupation of restored sites was accelerated by the presence of adjacent mature riparian habitat, which afforded birds nest sites and/or foraging habitat lacking in the planted vegetation. Vireos nesting in restored habitat achieved success comparable to that of vireos nesting in surrounding natural habitat, and there was no evidence that productivity was reduced in created areas. These findings indicate that creating nesting habitat for this target species is feasible and suggest that the critical components of vireo nesting habitat have been captured in both the design and quantitative assessment of restoration sites.

Restoration Ecology↗

USGS2006

Effects of El Niño on distribution and reproductive performance of Black Brant

Climate in low-latitude wintering areas may influence temperate and high-latitude breeding populations of birds, but demonstrations of such relationships have been rare because of difficulties in linking wintering with breeding populations. We used long-term aerial surveys in Mexican wintering areas and breeding areas in Alaska, USA, to assess numbers of Black Brant ( Branta bernicla nigricans ; hereafter brant) on their principal wintering and breeding area in El Niño and non-El Niño years. We used Pollock's robust design to directly estimate probability of breeding and apparent annual survival of individually marked brant at the Tutakoke River (TR) colony, Alaska, in each year between 1988 and 2001. Fewer brant wintered in Mexico during every El Niño event since 1965. Fewer brant were observed on the principal breeding area following each El Niño since surveys began in 1985. Probability of breeding was negatively related to January sea surface temperature along the subtropical coast of North America during the preceding winter. Between 23% (five-year-olds or older) and 30% (three-year-olds) fewer brant nested in 1998 following the strong El Niño event in the winter of 1997–1998 than in non-El Niño years. This finding is consistent with life history theory, which predicts that longer-lived species preserve adult survival at the expense of reproduction. Oceanographic conditions off Baja California, apparently by their effect on Zostera marina (eelgrass), strongly influence winter distribution of brant geese and their reproduction (but not survival), which in turn affects ecosystem dynamics in Alaska.

Alaska↗

USGS2023

Interstate 15 wildlife crossing design considerations for focal wildlife species - Santa Ana-Palomar Mountains Linkage southern California

The Nature Conservancy (TNC) and the California Department of Transportation (Caltrans), along with landowners including San Diego State University, California Department of Fish and Wildlife, Western Riverside Regional Conservation Authority and Riverside County Flood Control District are developing wildlife crossing infrastructure projects along a 3-mile stretch of Interstate 15 (I-15) in the Santa Ana-Palomar Mountains Linkage (hereafter ‘Linkage’) in southern California. These crossings will provide a critical missing link that will help reconnect wildlife in the coastal Santa Ana Mountains west of I-15 with those in the interior Palomar and Eastern Peninsular ranges to the east of I-15. The Linkage supports intact and diverse habitats including coastal sage scrub, grasslands, chaparral, and oak and riparian woodlands, and has been a focus of regional conservation efforts for the last 30 years. The three wildlife crossing infrastructure projects include enhancement of the existing Temecula Creek I-15 Bridge, construction of a new vegetated wildlife overcrossing, and construction of a new stand-alone wildlife culvert. Given the challenges and level of financial investment required to secure wildlife crossings for I-15 in the Linkage, TNC and Caltrans proposed that planning efforts would benefit from input by taxonomic experts on design concepts that meet the needs of the broadest range of wildlife. While wildlife crossings are becoming more common, optimal designs that meet the needs of a variety of wildlife species are largely unknown and can be site specific. To address this challenge, we held a workshop in February 2022 that brought together over 50 wildlife experts to brainstorm and identify specific design considerations for various focal wildlife species groups (medium/large mammals, small animals, birds, bats, plants, and invertebrates) that might use the identified I-15 wildlife crossings (The Nature Conservancy 2022). Lead experts for each focal species group worked together to identify specific wildlife crossing features or attributes for each of the three proposed wildlife crossings. Specific attributes evaluated by experts for each crossing type and species group included, at a minimum: • Crossing Structure Attributes; o Habitat features? (cover, habitat structure, substrate, moisture, light and noise mitigation) • Crossing Approach Area Features; o Habitat features (cover type/density, substrate, water, light and noise mitigation) • Barrier design to reduce roadkill and/or to funnel wildlife to the crossing; • Additional research to resolve uncertainties related to crossing design Based on the design considerations for each potential crossing type, the experts then weighed in on the suitability of the existing location and probability of use by their focal species or groups of species. With proposed design features, Temecula Creek Bridge has moderate or high probability of use by 27 of the 36 focal wildlife species assessed, while the vegetated overcrossing could meet the needs of 26 of the 36 species. When combined, Temecula Creek Bridge and the vegetated overcrossing have a moderate or high probability of use for 34 of the 36 species. The wildlife culvert has a moderate or high level of expected use by 10 of the 36 focal species and could serve connectivity needs for representative species from all but the bird and plant species groups.

California↗

USGS2001

Contaminant profiles of two species of shorebirds foraging together at two neighboring sites in south San Francisco Bay, California

The San Francisco Bay estuary isused by over one million shorebirds during springmigration and is home to several hundred thousandduring the winter. Most shorebird use occurs in thesouthern reach of the estuary (South Bay). Thereduced water circulation and discharge fromindustrial sources in the South Bay are responsiblefor the highest levels of some trace elements in theestuary. Wintering shorebirds have been found to havestrong site fidelity to areas as small as a fewkilometers in the South Bay, which may increase theirexposure to contaminants near local point sources. Inaddition, different shorebird species foraging at thesame site have been shown to have differentcontaminant burdens. Thus, our objectives were totest whether contaminant burdens differed by species,or whether contaminant burdens differed in shorebirdscollected at adjacent sites. We examined thecontaminant profiles of two species of shorebirds,long-billed dowitchers ( Limnodromus scolopaceus )and western sandpipers ( Calidris mauri ) thatforage together at two sites, Hayward and Newark,separated by 8 km in the South Bay. We usedmultivariate analysis of variance tests to compare thecomposition of 14 elemental analytes in their livertissues and estimated their molar ratios of Hg and Se. Composite samples were used for contaminant analysesbecause of the small body size of the shorebirds. Seven elemental analytes (Ag, Ba, Be, Cr, Ni, Pb, V)were below detection limits in a majority of thesamples so statistical analyses were precluded. Inthe measurable analytes (As, Cd, Cu, Hg, Mn, Se, Zn),we found no significant intra-site differences ofcontaminant profiles for the two species. We pooledthe samples to examine inter-site differences andfound significant differences in contaminant profilesbetween shorebirds at the neighboring sites ( P = 0.03). Shorebirds at Newark had higher ( P < 0.05) concentrations of As, Cd, and Se than those at Hayward. Dowitchers at Newark had concentrations of Hg and Se which were highly correlated ( P < 0.003) in a mean molar ratio of 1:19, similar tothat reported in other birds. In the larger dowitcherspecies, we also examined exposure to 20organochlorine compounds. Organic analyses showedthat the dowitchers had been exposed to DDE, PCBs,dieldrin and trans-nonachlor, but with no significantdifferences in concentrations between Hayward andNewark ( P > 0.05).

Environmental Monitoring and Assessment↗

USGS2008

An evaluation of the evolution of the latest miocene to earliest pliocene bouse lake system in the lower Colorado river valley, southwestern USA

The upper Miocene to lower Pliocene Bouse Formation in the lower Colorado River trough of the American Southwest was deposited in three basins - from north to south, the Mohave, Havasu, and Blythe Basins - that were formed by extensional fault ing in the early to middle Miocene. Fossils of marine, brackish, and freshwater organ isms in the Bouse Formation have been interpreted to indicate an estuarine environment associated with early opening of the nearby Gulf of California. Regional uplift since 5 Ma is required to position the estuarine Bouse Formation at present elevations as high as 555 m, where greater uplift is required in the north. We present a compilation of Bouse Formation elevations that is consistent with Bouse deposition in lakes, with an abrupt 225 m northward increase in maximum Bouse elevations at Topock gorge north of Lake Havasu. Within Blythe and Havasu Basins, maximum Bouse elevations are 330 m above sea level in three widely spaced areas and reveal no evidence of regional tilting. To the north in Mohave Basin, numerous Bouse outcrops above 480 m elevation include three widely spaced sites where the Bouse Formation is exposed at 536-555 m. Numerical simulations of initial Colorado River inflow to a sequence of closed basins along the lower Colorado River corridor model a history of lake filling, spilling, evaporation and salt concentration, and outflow-channel incision. The simulations support the plausibility of evaporative concentration of Colorado River water to seawater-level salinities in Blythe Basin and indicate that such salinities could have remained stable for as long as 20-30 k.y. We infer that fossil marine organ isms in the Bouse Formation, restricted to the southern (Blythe) basin, reflect coloniza tion of a salty lake by a small number of species that were transported by birds.

Conference Paper↗

USGS2018

Modeling resource selection of bobcats (Lynx rufus) and vertebrate species distributions in Orange County, southern California

For nature reserves in urban settings, wildlife and wildlife habitats may be affected by recreational activities and intensive, adjacent development. Sustaining biodiversity in such reserves is a challenge for land and natural resource managers, but identification of core areas and key resources for wildlife species may help in planning for current and emerging threats. To help identify core areas and resources, we conducted spatial analyses and predictive modeling of vertebrate distributions for a network of nature reserves in densely populated Orange County, California. We primarily focused on bobcats ( Lynx rufus ), a species with a strong association with natural habitat. Bobcat space use has been correlated with broad, simple land-use categories, but relatively little is known about the influence of greater landscape complexity on habitat suitability for bobcats. To examine habitat selection by bobcats, we developed spatial data layers representing environmental factors that might influence this species, and we used previously collected Global Positioning System tracking data for 30 male and 21 female bobcats to indicate bobcat response to complex landscape factors. We examined these inputs using Resource Selection Function (RSF) modeling and developed spatially explicit models of the probability of bobcat use (selection or avoidance) of landscape characteristics. RSF models highlighted the general importance of reserve habitat for bobcats, but suggested that female bobcats were more dependent that male bobcats on habitat within designated reserves. Male bobcats, which range more widely than female bobcats, were associated with undeveloped areas both within and outside reserves. Small areas were present outside reserves that seemed to provide additional suitable habitat or movement areas for bobcats, potentially through restoration, connectivity, or reduced edge effects. Although bobcat RSFs suggested areas of high value to this species and potentially other species, taxa can differ greatly in their resource-selection and spatial requirements. Thus, for several species of reptiles, amphibians, and birds, we adapted species distribution models based on occurrence data to examine the response of other vertebrates to the landscape. To identify potential High-Value Areas (HVAs) for single or multiple species, we then developed a step-wise filtering process that can be applied to a series of spatial data layers. We provide examples of alternative decision models for HVAs that capture different elements of biodiversity and a range of management considerations. As landscape and management challenges change, these spatial layers and decision rules can be adjusted based on new information. Our approach thus establishes a general framework for identifying high-value habitat that can be used for current management decisions and refined in the future, depending on management interests and goals and the availability of suitable quality data or adequate surrogate information.

California↗