Abstract During drought, the tree subpopulations (such as size or vigour classes) that suffer disproportionate mortality can be conceptually arrayed along a continuum defined by actions of biotic agents, particularly insects. At one extreme, stress dominates: insects are absent simply kill most physiologically stressed trees. opposite host selection outbreaking trees independently their stress, instead selecting based on other traits. Intermediate responses also possible. Yet for...

We assessed methylmercury (MeHg) demethylation in the livers of adults and chicks four waterbird species that commonly breed San Francisco Bay: American avocets, black-necked stilts, Caspian terns, Forster's terns. In (all combined), we found strong evidence for a threshold model where MeHg occurred above hepatic total mercury concentration 8.51 +/- 0.93 microg/g dry weight, there was decline %MeHg values as (THg) concentrations increased weight. Conversely, no chicks, declined linearly with...

Abstract Birds are used as bioindicators of environmental mercury (Hg) contamination, and toxicity reference values needed for injury assessments. We conducted a comprehensive review, summarized data from 168 studies, performed series Bayesian hierarchical meta‐analyses, developed new the effects methylmercury (MeHg) on birds using benchmark dose analysis framework. Lethal sublethal MeHg were categorized into nine biologically relevant endpoint categories three age classes. Effective Hg...

The development of anthropogenic structures, especially those related to energy resources, in sagebrush ecosystems is an important concern among developers, conservationists, and land managers relation greater sage-grouse (Centrocercus urophasianus; hereafter, sage-grouse) populations. Sage-grouse are dependent on meet their seasonal life-phase requirements, research indicates that structures can adversely affect Land management agencies have attempted reduce the negative effects by...

Renewable energy production can kill individual birds, but little is known about how it affects avian populations. We assessed the vulnerability of populations for 23 priority bird species killed at wind and solar facilities in California, USA. Bayesian hierarchical models suggested that 48% these were vulnerable to population-level effects from added fatalities caused by renewables other sources. Effects extended far beyond location impact distant regions across continental migration...

We investigated the effect of recent habitat changes in California's Central Valley on wintering Pacific greater white-fronted geese (Anser albifrons frontalis) by comparing roost-to-feed distances, distributions, population range sizes, and use during 1987–1990 1998–2000. These included wetland restoration agricultural land enhancement due to 1990 implementation Joint Venture, increased area used for rice (Oryza sativa) production, practice flooding, rather than burning, straw residues...

Following field observations of wild Agassiz's desert tortoises (Gopherus agassizii) with oral lesions similar to those seen in captive herpesvirus infection, we measured the prevalence antibodies Testudinid (TeHV) 3 populations California. The survey revealed 30.9% antibody prevalence. In 2009 and 2010, two adult male tortoises, gross consistent trauma puncture wounds, respectively, were necropsied. Tortoise 1 was from central Mojave Desert tortoise 2 northeastern Desert. We extracted DNA...

Abstract Extensive global estuarine wetland losses have prompted intensive focus on restoration of these habitats. In California, substantial tracts freshwater, brackish and tidal wetlands been lost. Given the anthropogenic footprint development urbanization in this region, must rely conversion existing habitat types rather than adding new wetlands. These restorations can cause conflicts among stakeholders species that win or lose depending identified priorities. Suisun Marsh San Francisco...

Significance Kelp forests are declining worldwide due to varied combinations of environmental change and the trophic downgrading urchin-controlling predators. These processes have increased frequency extent rapid, nonlinear shifts so-called urchin barrens whose ecological functioning services reduced relative those kelp forests. Understanding factors that regulate kelp-forest tipping points switches between states is key their management. Here we demonstrate substrate complexity (surface...

ABSTRACT The influence of habitat, waterfowl abundance, and hunting on winter survival is not well understood. We studied late August‐March 163 after‐hatch‐year (AHY) 128 hatch‐year (HY) female mallards ( Anas platyrhynchos ) radiotagged in Sacramento Valley (SACV) 885 AHY northern pintails A. acuta throughout the Central California, USA, relative to flooded habitat (HAB), January abundance each species (JMAL or JPIN), hunter‐days (HDY), a pressure index (HPI) that combined these variables....

Bird eggs are commonly used in contaminant monitoring programs and toxicological risk assessments, but intraclutch variation sampling methodology could influence interpretability. The authors examined the of egg-laying sequence on egg mercury concentrations burdens American avocets, black-necked stilts, Forster's terns. average decline between first last laid was 33% for 22% terns, 11% most this occurred second (24% 18% 9% avocets). Trends size with order were inconsistent among species,...

ABSTRACT The recovery of large carnivore species from over‐exploitation can have socioecological effects; thus, reliable estimates potential abundance and distribution represent a valuable tool for developing management objectives criteria. For sea otters ( Enhydra lutris ), as with many apex predators, equilibrium is not constant across space but rather varies function local habitat quality resource dynamics, thereby complicating the extrapolation carrying capacity K ) one location to...

Numerous factors have contributed to declines in populations of the federally threatened Agassiz's Desert Tortoise (Gopherus agassizii) and continue limit recovery. In 2010, we surveyed a low-density population on military test facility northwestern Mojave California, USA, evaluate status identify potential contributing distribution low densities. Estimated densities live tortoises ranged spatially from 1.2/km2 15.1/km2. Although only one death breeding-age tortoise was recorded for 4-yr...

ABSTRACT Waterfowl managers lack the information needed to fully evaluate biological effects of their habitat conservation programs. We studied body condition dabbling ducks shot by hunters at public hunting areas throughout Central Valley California during 2006–2008 compared with from 1979 1993. These time periods coincide increases due Joint Venture programs and changing agricultural practices; we modeled ascertain whether differed among waterfowl these periods. Three dataset comparisons...

Breeding success should increase with prior knowledge of the surrounding environment, which is dependent upon an animal's ability to evaluate habitat. Prospecting for nesting locations and migratory stopover sites are well-established behaviours among bird species. We assessed whether three species California dabbling ducks – mallards, Anas platyrhynchos, gadwall, Mareca strepera, cinnamon teal, Spatula cyanoptera in Suisun Marsh, California, U.S.A., a brackish marsh, prospect suitable...

We quantified patterns in stream temperature a northern coastal California river using thermal infrared (TIR) imaging and in-stream monitoring related to the historical present distributions of juvenile coho salmon (Oncorhynchus kisutch). In Redwood Creek, California, water increased from headwaters about 60 km downstream, then gradually decreased over next 40 as approaches Pacific Ocean. Despite lack fish migration barriers, are currently only observed downstream-most 20 km, whereas...

First posted September 24, 2019 For additional information, contact: Director, Western Ecological Research CenterU.S. Geological Survey3020 State University Drive EastSacramento, California 95819 The census of southern sea otters (Enhydra lutris nereis), also known as otters, was conducted from early May to July along the mainland coast central and in April at San Nicolas Island California. range-wide index, defined 3-year average combined counts range Island, 2,962, a decrease 166 index for...

ABSTRACT Agassiz’s desert tortoise ( Gopherus agassizii ), a threatened species of the southwestern United States, has severely declined to point where 76% populations in critical habitat (Tortoise Conservation Areas) are below viability. The potential for rapid recovery wild is low because females require 12–20 years reach reproductive maturity and produce few eggs annually. We report on 34‐year mark‐recapture study tortoises initiated 1979 at Desert Tortoise Research Natural Area western...