Geology topics

John Y. Takekawa

Publications and source records attributed to John Y. Takekawa.

At least 109 records · Page 6Linked to original sources

USGS2013

Wetland Accretion Rate Model of Ecosystem Resilience (WARMER) and its application to habitat sustainability for endangered species in the San Francisco Estuary

Salt marsh faunas are constrained by specific habitat requirements for marsh elevation relative to sea level and tidal range. As sea level rises, changes in relative elevation of the marsh plain will have differing impacts on the availability of habitat for marsh obligate species. The Wetland Accretion Rate Model for Ecosystem Resilience (WARMER) is a 1-D model of elevation that incorporates both biological and physical processes of vertical marsh accretion. Here, we use WARMER to evaluate changes in marsh surface elevation and the impact of these elevation changes on marsh habitat for specific species of concern. Model results were compared to elevation-based habitat criteria developed for marsh vegetation, the endangered California clapper rail (Rallus longirostris obsoletus), and the endangered salt marsh harvest mouse (Reithrodontomys raviventris) to determine the response of marsh habitat for each species to predicted >1-m sea-level rise by 2100. Feedback between vertical accretion mechanisms and elevation reduced the effect of initial elevation in the modeled scenarios. Elevation decreased nonlinearly with larger changes in elevation during the latter half of the century when the rate of sea-level rise increased. Model scenarios indicated that changes in elevation will degrade habitat quality within salt marshes in the San Francisco Estuary, and degradation will accelerate in the latter half of the century as the rate of sea-level rise accelerates. A sensitivity analysis of the model results showed that inorganic sediment accumulation and the rate of sea-level rise had the greatest influence over salt marsh sustainability.

California↗

USGS2013

Movements of wild ruddy shelducks in the Central Asian Flyway and their spatial relationship to outbreaks of highly pathogenic avian influenza H5N1

Highly pathogenic avian influenza H5N1 remains a serious concern for both poultry and human health. Wild waterfowl are considered to be the reservoir for low pathogenic avian influenza viruses; however, relatively little is known about their movement ecology in regions where HPAI H5N1 outbreaks regularly occur. We studied movements of the ruddy shelduck ( Tadorna ferruginea ), a wild migratory waterfowl species that was infected in the 2005 Qinghai Lake outbreak. We defined their migration with Brownian Bridge utilization distribution models and their breeding and wintering grounds with fixed kernel home ranges. We correlated their movements with HPAI H5N1 outbreaks, poultry density, land cover, and latitude in the Central Asian Flyway. Our Akaike Information Criterion analysis indicated that outbreaks were correlated with land cover, latitude, and poultry density. Although shelduck movements were included in the top two models, they were not a top parameter selected in AICc stepwise regression results. However, timing of outbreaks suggested that outbreaks in the flyway began during the winter in poultry with spillover to wild birds during the spring migration. Thus, studies of the movement ecology of wild birds in areas with persistent HPAI H5N1 outbreaks may contribute to understanding their role in transmission of this disease.

Viruses↗

USGS2013

Flying with the wind: Scale dependency of speed and direction measurements in modelling wind support in avian flight

Background : Understanding how environmental conditions, especially wind, influence birds' flight speeds is a prerequisite for understanding many important aspects of bird flight, including optimal migration strategies, navigation, and compensation for wind drift. Recent developments in tracking technology and the increased availability of data on large-scale weather patterns have made it possible to use path annotation to link the location of animals to environmental conditions such as wind speed and direction. However, there are various measures available for describing not only wind conditions but also the bird's flight direction and ground speed, and it is unclear which is best for determining the amount of wind support (the length of the wind vector in a bird’s flight direction) and the influence of cross-winds (the length of the wind vector perpendicular to a bird’s direction) throughout a bird's journey. Results : We compared relationships between cross-wind, wind support and bird movements, using path annotation derived from two different global weather reanalysis datasets and three different measures of direction and speed calculation for 288 individuals of nine bird species. Wind was a strong predictor of bird ground speed, explaining 10-66% of the variance, depending on species. Models using data from different weather sources gave qualitatively similar results; however, determining flight direction and speed from successive locations, even at short (15 min intervals), was inferior to using instantaneous GPS-based measures of speed and direction. Use of successive location data significantly underestimated the birds' ground and airspeed, and also resulted in mistaken associations between cross-winds, wind support, and their interactive effects, in relation to the birds' onward flight. Conclusions : Wind has strong effects on bird flight, and combining GPS technology with path annotation of weather variables allows us to quantify these effects for understanding flight behaviour. The potentially strong influence of scaling effects must be considered and implemented in developing sampling regimes and data analysis.

Movement Ecology↗

USGS2013

The paradox of extreme high-altitude migration in bar-headed geese Anser indicus

Bar-headed geese are renowned for migratory flights at extremely high altitudes over the world's tallest mountains, the Himalayas, where partial pressure of oxygen is dramatically reduced while flight costs, in terms of rate of oxygen consumption, are greatly increased. Such a mismatch is paradoxical, and it is not clear why geese might fly higher than is absolutely necessary. In addition, direct empirical measurements of high-altitude flight are lacking. We test whether migrating bar-headed geese actually minimize flight altitude and make use of favourable winds to reduce flight costs. By tracking 91 geese, we show that these birds typically travel through the valleys of the Himalayas and not over the summits. We report maximum flight altitudes of 7290 m and 6540 m for southbound and northbound geese, respectively, but with 95 per cent of locations received from less than 5489 m. Geese travelled along a route that was 112 km longer than the great circle (shortest distance) route, with transit ground speeds suggesting that they rarely profited from tailwinds. Bar-headed geese from these eastern populations generally travel only as high as the terrain beneath them dictates and rarely in profitable winds. Nevertheless, their migration represents an enormous challenge in conditions where humans and other mammals are only able to operate at levels well below their sea-level maxima.

Proceedings of the Royal Society B↗

USGS2013

Post-release survival of surf scoters following an oil spill: an experimental approach to evaluating rehabilitation success

Birds are often the most numerous vertebrates damaged and rehabilitated in marine oil spills; however, the efficacy of avian rehabilitation is frequently debated and rarely examined experimentally. We compared survival of three radio-marked treatment groups, oiled, rehabilitated (ORHB), un-oiled, rehabilitated (RHB), and un-oiled, non-rehabilitated (CON), in an experimental approach to examine post-release survival of surf scoters ( Melanitta perspicillata ) following the 2007 M/V Cosco Busan spill in San Francisco Bay. Live encounter-dead recovery modeling indicated that survival differed among treatment groups and over time since release. The survival estimate (±SE) for ORHB was 0.143 ± 0.107 compared to CON (0.498 ± 0.168) and RHB groups (0.772 ± 0.229), suggesting scoters tolerated the rehabilitation process itself well, but oiling resulted in markedly lower survival. Future efforts to understand the physiological effects of oil type and severity on scoters are needed to improve post-release survival of this species.

California↗

USGS2013

American Avocet (Recurvirostra americana)

This large, striking shorebird with long bluish-gray legs, a long recurved bill, and a black-and-white chevron pattern on its back and wings is one of four Avocet species in the world, the only one with distinct breeding and non-breeding plumages -- its grayish-white head and neck feathers become cinnamon in early spring as birds begin to form pairs and migrate to breeding areas.

Book chapter↗

USGS2013

Final report for sea-level rise response modeling for San Francisco Bay estuary tidal marshes

The International Panel on Climate Change has identified coastal ecosystems as areas that will be disproportionally affected by climate change. Current sea-level rise projections range widely with 0.57 to 1.9 meters increase in mea sea level by 2100. The expected accelerated rate of sea-level rise through the 21 st century will put many coastal ecosystems at risk, especially those in topographically low-gradient areas. We assessed marsh accretion and plant community state changes through 2100 at 12 tidal salt marshes around San Francisco Bay estuary with a sea-level rise response model. Detailed ground elevation, vegetation, and water level data were collected at all sites between 2008 and 2011 and used as model inputs. Sediment cores (taken by Callaway and others, 2012) at four sites around San Francisco Bay estuary were used to estimate accretion rates. A modification of the Callaway and others (1996) model, the Wetland Accretion Rate Model for Ecosystem Resilience (WARMER), was utilized to run sea-level rise response models for all sites. With a mean sea level rise of 1.24 m by 2100, WARMER projected that the vast majority, 95.8 percent (1,942 hectares), of marsh area in our study will lose marsh plant communities by 2100 and to transition to a relative elevation range consistent with mudflat habitat. Three marshes were projected to maintain marsh vegetation to 2100, but they only composed 4.2 percent (85 hectares) of the total marsh area surveyed.

California↗

USGS2013

Internal nutrient sources and nutrient distributions in Alviso Pond A3W, California

Within the Alviso Salt Pond complex, California, currently undergoing avian-habitat restoration, pore-water profilers (U.S. Patent 8,051,727 B1) were deployed in triplicate at two contrasting sites in Pond A3W (“Inlet”, near the inflow, and “Deep”, near the middle of the pond; figs. 1 and 2; table 1, note that tables in this report are provided online only as a .xlsx workbook at http://pubs.usgs.gov/of/2013/1128/). Deployments were conducted in 2010 and 2012 during the summer algal-growth season. Specifically, three deployments, each about 7 weeks apart, were undertaken each summer. This study provides the first measurements of the diffusive flux of nutrients across the interface between the pond bed and water column (that is, benthic nutrient flux). These nutrient fluxes are crucial to pond restoration efforts because they typically represent a major (if not the greatest) source of nutrients to the water column in both ponds and other lentic systems. For soluble reactive phosphorus (SRP, the most biologically available form in solution), benthic flux was positive both years (that is, out of the sediment into the water column; table 2), with the exception of the August 2010 deployment, which exhibited nearly negligible but negative flux. Overall, the average SRP flux was significantly greater at Deep (23.9 ± 8.6 micromoles per square meter per hour (µmol-m -2 -h -1 ); all errors shown reflect the 95-percent confidence interval) than Inlet (12.6 ± 4.9 µmol-m -2 -h -1 ). There was much greater temporal variability in SRP flux in the pond than reported for the lower estuary (Topping and others, 2001). For dissolved ammonia, benthic flux was consistently positive on all six sampling trips, and similar to SRP, the fluxes at Deep (258 ± 49 µmol-m -2 -h -1 ) were consistently greater than those at Inlet (28 ± 11 µmol-m -2 -h -1 ). Dissolved ammonia fluxes reported for South San Francisco Bay by Topping and others (2001) fall in between these values. Once again, greater variability for benthic fluxes determined in the pond was observed relative to adjacent South San Francisco Bay. With the near absence of any measurable concentration gradient, dissolved-nitrate fluxes were consistently negligible in the pond. Silica fluxes are often used to represent sediment diagenetic processes that biogeochemically cycle silica (an important algal macronutrient) between biogenic and inorganic phases (Fanning and Pilson, 1974; Emerson and others, 1984). For South San Francisco Bay, those values are consistently positive from core-incubation experiments. In Pond A3W, dissolved-silica fluxes averaged 49 ± 25 µmol-m -2 -h -1 at Inlet and were much higher at Deep (482 ± 370 µmol-m -2 -h -1 ), similar to the spatially variability observed for SRP and dissolved ammonia. An elevated silica flux can stimulate diatom production and subsequent eutrophication effects. Variability in these silica fluxes is consistent with season patterns in pond primary productivity. On the basis of comparisons of dissolved-oxygen flux measurements by profilers and core incubations, it appears that diffusive flux estimates for the sediment in this pond, as one might expected in such benthically productive environments, result in a significant underestimation of true sediment oxygen demand. Therefore, a core incubation experiment was conducted to better quantify the demand. To complement these benthic-flux studies, a diurnal study of nutrient advective flux into and out of the pond was measured during neap and spring tides to provide comparative estimates for allochthonous solute transport (Garret, 2012). Using the two different tides as the probable upper and lower boundaries, we can estimate a range of probable values throughout the year. After converting this advective flux into kg/yr, we can compare it directly to benthic flux estimates for the pond extrapolated over the 2.27 square kilometer (km 2 ) pond surface. Benthic flux of nitrogen species, averaged over all sites and dates, was about 80,000 kilograms per year (kg/yr), well above the adjective flux range of -50 to 1,500 kg/yr. By contrast, the average benthic flux of orthophosphate was about 12,000 kg/yr, well below the advective flux range of 21,500 to 30,000 kg/yr. Initial benthic flux estimates were also made for trace metals, including copper, nickel, iron, and manganese. These analyses indicated that the two sites, Inlet and Deep, have different pore-water profiles, with Inlet exhibiting much higher benthic flux estimates for nickel, iron, and manganese. These initial benthic-flux values reported for macronutrients are particularly impressive in magnitude when one considers that diffusive flux of dissolved solutes based on pore-water profiles provides a conservative determination that may be enhanced by other biogeochemical processes. These enhancement processes (Boudreau and Jorgensen, 2001) include bioturbation, bioirrigation, wind resuspension, and potential groundwater inflows, some of which are captured in core-incubation experiments (Kuwabara and others, 2009). Hence, the values reported herein represent lower bounds to indicate the potential importance of such internal solute sources. The elevated diffusive fluxes for nutrients in the pond relative to the adjacent estuary indicate that vertical nutrient transport between the pond bed and water column is consistently an important (and at times the most important) source of nutrients that stimulate phytoplankton growth in the water column. One might therefore reasonably hypothesize that this benthic transport of biologically reactive solutes (both nutrients and toxicants) represents the most important step at the base of the food web for trophic transfer.

California↗

USGS2013

Mapping risk of avian influenza transmission at the interface of domestic poultry and wild birds

Emergence of avian influenza viruses with high lethality to humans, such as the currently circulating highly pathogenic A(H5N1) (emerged in 1996) and A(H7N9) cause serious concern for the global economic and public health sectors. Understanding the spatial and temporal interface between wild and domestic populations, from which these viruses emerge, is fundamental to taking action. This information, however, is rarely considered in influenza risk models, partly due to a lack of data. We aim to identify areas of high transmission risk between domestic poultry and wild waterfowl in China, the epicenter of both viruses. Two levels of models were developed: one that predicts hotspots of novel virus emergence between domestic and wild birds, and one that incorporates H5N1 risk factors, for which input data exists. Models were produced at 1 and 30 km spatial resolution, and two temporal seasons. Patterns of risk varied between seasons with higher risk in the northeast, central-east, and western regions of China during spring and summer, and in the central and southeastern regions during winter. Monte-Carlo uncertainty analyses indicated varying levels of model confidence, with lowest errors in the densely populated regions of eastern and southern China. Applications and limitations of the models are discussed within.

Frontiers in Public Health↗

USGS2013

GPS location history data mining and anomalous detection: the scenario of bar-headed geese migration

It is important to discover common movement sequences and uncommon behaviors during the migration of wild birds. In this paper, we propose a new approach to analyze the GPS location history data of migratory birds. The stopover sites are first extracted from the location history data of birds, and their movement sequences are generated automatically. Then, a consistency calculation method is introduced for calculating the movement sequence consistency degrees among the birds. The common movement sequences and uncommon behaviors can be recognized on the basis of consistency. We conducted experiments on the data collected from bar-headed geese captured in the Qinghai Lake region. The experiment results indicate the correctness of our approach.

Book chapter↗

USGS2013

Storm surges and climate change implications for tidal marshes: Insight from the San Francisco Bay Estuary, California, USA

Tidal marshes are dynamic ecosystems, which are influenced by oceanic and freshwater processes and daily changes in sea level. Projected sea-level rise and changes in storm frequency and intensity will affect tidal marshes by altering suspended sediment supply, plant communities, and the inundation duration and depth of the marsh platform. The objective of this research was to evaluate if regional weather conditions resulting in low-pressure storms changed tidal conditions locally within three tidal marshes. We hypothesized that regional storms will increase sea level heights locally, resulting in increased inundation of the tidal marsh platform and plant communities. Using site-level measurements of elevation, plant communities, and water levels, we present results from two storm events in 2010 and 2011 from the San Francisco Bay Estuary (SFBE), California, USA. The January 2010 storm had the lowest recorded sea level pressure in the last 30 years for this region. During the storm episodes, the duration of tidal marsh inundation was 1.8 and 3.1 times greater than average for that time of year, respectively. At peak storm surges, over 65% in 2010 and 93% in 2011 of the plant community was under water. We also discuss the implications of these types of storms and projected sea-level rise on the structure and function of the tidal marshes and how that will impact the hydro-geomorphic processes and marsh biotic communities.

California↗

USGS2012

Migration strategy affects avian influenza dynamics in mallards ( Anas platyrhynchos ).

Studies of pathogen transmission typically overlook that wildlife hosts can include both migrant and resident populations when attempting to model circulation. Through the application of stable isotopes in flight feathers, we estimated the migration strategy of mallards ( Anas platyrhynchos ) occurring on California wintering grounds. Our study demonstrates that mallards- a principal host of avian influenza virus (AIV) in nature, contribute differently to virus gene flow depending on migration strategy. No difference in AIV prevalence was detected between resident (9.6%), intermediate-distance (9.6%) and long-distance migrants (7.4%). Viral diversity among the three groups was also comparable, possibly owing to viral pool mixing when birds converge at wetlands during winter. However, migrants and residents contributed differently to the virus gene pool at wintering wetlands. Migrants introduced virus from northern breeding grounds (Alaska and the NW Pacific Rim) into the wintering population, facilitating gene flow at continental scales, but circulation of imported virus appeared to be limited. In contrast, resident mallards acted as AIV reservoirs facilitating year-round circulation of limited subtypes (i.e. H5N2) at lower latitudes. This study supports a model of virus exchange in temperate regions driven by the convergence of wild birds with separate geographic origins and exposure histories.

Molecular Ecology↗

USGS2012

Range-wide patterns of migratory connectivity in the western sandpiper Calidris mauri

Understanding the population dynamics of migratory animals and predicting the consequences of environmental change requires knowing how populations are spatially connected between different periods of the annual cycle. We used stable isotopes to examine patterns of migratory connectivity across the range of the western sandpiper Calidris mauri . First, we developed a winter isotope basemap from stable-hydrogen (δD), -carbon (δ 13 C), and -nitrogen (δ 15 N) isotopes of feathers grown in wintering areas. δD and δ 15 N values from wintering individuals varied with the latitude and longitude of capture location, while δ 13 C varied with longitude only. We then tested the ability of the basemap to assign known-origin individuals. Sixty percent of wintering individuals were correctly assigned to their region of origin out of seven possible regions. Finally, we estimated the winter origins of breeding and migrant individuals and compared the resulting empirical distribution against the distribution that would be expected based on patterns of winter relative abundance. For breeding birds, the distribution of winter origins differed from expected only among males in the Yukon-Kuskokwim (Y-K) Delta and Nome, Alaska. Males in the Y-K Delta originated overwhelmingly from western Mexico, while in Nome, there were fewer males from western North America and more from the Baja Peninsula than expected. An unexpectedly high proportion of migrants captured at a stopover site in the interior United States originated from eastern and southern wintering areas, while none originated from western North America. In general, we document substantial mixing between the breeding and wintering populations of both sexes, which will buffer the global population of western sandpipers from the effects of local habitat loss on both breeding and wintering grounds.

Journal of Avian Biology↗

USGS2012

Eco-virological approach for assessing the role of wild birds in the spread of avian influenza H5N1 along the central Asian flyway

A unique pattern of highly pathogenic avian influenza (HPAI) H5N1 outbreaks has emerged along the Central Asia Flyway, where infection of wild birds has been reported with steady frequency since 2005. We assessed the potential for two hosts of HPAI H5N1, the bar-headed goose ( Anser indicus ) and ruddy shelduck ( Tadorna tadorna ), to act as agents for virus dispersal along this ‘thoroughfare’. We used an eco-virological approach to compare the migration of 141 birds marked with GPS satellite transmitters during 2005–2010 with: 1) the spatio-temporal patterns of poultry and wild bird outbreaks of HPAI H5N1, and 2) the trajectory of the virus in the outbreak region based on phylogeographic mapping. We found that biweekly utilization distributions (UDs) for 19.2% of bar-headed geese and 46.2% of ruddy shelduck were significantly associated with outbreaks. Ruddy shelduck showed highest correlation with poultry outbreaks owing to their wintering distribution in South Asia, where there is considerable opportunity for HPAI H5N1 spillover from poultry. Both species showed correlation with wild bird outbreaks during the spring migration, suggesting they may be involved in the northward movement of the virus. However, phylogeographic mapping of HPAI H5N1 clades 2.2 and 2.3 did not support dissemination of the virus in a northern direction along the migration corridor. In particular, two subclades (2.2.1 and 2.3.2) moved in a strictly southern direction in contrast to our spatio-temporal analysis of bird migration. Our attempt to reconcile the disciplines of wild bird ecology and HPAI H5N1 virology highlights prospects offered by both approaches as well as their limitations.

PLoS ONE↗

USGS2012

Will inundation and salinity levels associated with projected sea level rise reduce the survival, growth, and reproductive capacity of Sarcocornia pacifica (pickleweed)?

In the San Francisco Bay Estuary, CA, USA, sea level rise (SLR) is projected to increase by 1.4 m during the next 90 years resulting in increased inundation and salt water intrusion up-estuary. Since inundation and salinity are critical factors that drive vegetation structure and composition in coastal wetlands, we asked whether inundation and salinity levels associated with SLR would reduce the survival, growth, and reproductive capacity of a dominant halophyte, Sarcocornia pacifica (pickleweed). We conducted a 4 × 4 factorial greenhouse experiment to examine the effects of a range of inundation periods (25, 50, 75, and 100%) and water salinities (0, 10, 20, 30 psu) on individual S. pacifica adults and seedlings. We found that inundation and salinity treatments affected the height of adults and seedlings combined. When examined separately, adult height was negatively affected by inundation ≥75%, while seedling height was affected by the interaction of both inundation and salinity. Adult belowground biomass was negatively affected by complete inundation. Seedling aboveground biomass decreased 46% at the highest salinity (30 psu) and belowground biomass decreased at salinities ≥20 psu. Adult flower production was not affected by treatments but was reduced by 38% at 30 psu salinity for seedlings. While adult survival was 99%, seedling survival was 56% with greatest mortality at low (25%) inundation, possibly because their roots were more susceptible to desiccation. Vegetation structure of the marsh platform comprised of S. pacifica adults will be susceptible to greater inundation rates associated with SLR. Our results suggest that adults may grow less tall, thus altering the vegetation structure and likely the tidal marsh wildlife that rely on these habitats.

Aquatic Botany↗

USGS2012

Trajectory of early tidal marsh restoration: elevation, sedimentation and colonization of breached salt ponds in the northern San Francisco Bay

Tidal marsh restoration projects that cover large areas are critical for maintaining target species, yet few large sites have been studied and their restoration trajectories remain uncertain. A tidal marsh restoration project in the northern San Francisco Bay consisting of three breached salt ponds (≥300 ha each; 1175 ha total) is one of the largest on the west coast of North America. These diked sites were subsided and required extensive sedimentation for vegetation colonization, yet it was unclear whether they would accrete sediment and vegetate within a reasonable timeframe. We conducted bathymetric surveys to map substrate elevations using digital elevation models and surveyed colonizing Pacific cordgrass ( Spartina foliosa ). The average elevation of Pond 3 was 0.96 ± 0.19 m (mean ± SD; meters NAVD88) in 2005. In 2008–2009, average pond elevations were 1.05 ± 0.25 m in Pond 3, 0.81 ± 0.26 m in Pond 4, and 0.84 ± 0.24 m in Pond 5 (means ± SD; meters NAVD88). The largest site (Pond 3; 508 ha) accreted 9.5 ± 0.2 cm (mean ± SD) over 4 years, but accretion varied spatially and ranged from sediment loss in borrow ditches and adjacent to an unplanned, early breach to sediment gains up to 33 cm in more sheltered regions. The mean elevation of colonizing S. foliosa varied by pond (F = 71.20, df = 84, P < 0.0001) and was significantly lower in Ponds 4 and 5 compared with Pond 3 which corresponded with greater tidal muting in those ponds. We estimated 16% of Pond 3, 13% of Pond 4, and 24% of Pond 5 were greater than or equal to the median elevation of S. foliosa . Our results suggest that sedimentation to elevations that enable vegetation colonization is feasible in large sites with sufficient sediment loads although may occur more slowly compared with smaller sites.

California↗

USGS2012

Does mercury contamination reduce body condition of endangered California clapper rails?

We examined mercury exposure in 133 endangered California clapper rails ( Rallus longirostris obsoletus ) within tidal marsh habitats of San Francisco Bay, California from 2006 to 2010. Mean total mercury concentrations were 0.56 μg/g ww in blood (range: 0.15–1.43), 9.87 μg/g fw in head feathers (3.37–22.0), 9.04 μg/g fw in breast feathers (3.68–20.2), and 0.57 μg/g fww in abandoned eggs (0.15–2.70). We recaptured 21 clapper rails and most had low within-individual variation in mercury. Differences in mercury concentrations were largely attributed to tidal marsh site, with some evidence for year and quadratic date effects. Mercury concentrations in feathers were correlated with blood, and slopes differed between sexes ( R 2 = 0.58–0.76). Body condition was negatively related to mercury concentrations. Model averaged estimates indicated a potential decrease in body mass of 20–22 g (5–7%) over the observed range of mercury concentrations. Our results indicate the potential for detrimental effects of mercury contamination on endangered California clapper rails in tidal marsh habitats.

California↗

USGS2012

Cross-seasonal patterns of avian influenza virus in breeding and wintering migratory birds: a flyway perspective

The spread of avian influenza viruses (AIV) in nature is intrinsically linked with the movements of wild birds. Wild birds are the reservoirs for the virus and their migration may facilitate the circulation of AIV between breeding and wintering areas. This cycle of dispersal has become widely accepted; however, there are few AIV studies that present cross-seasonal information. A flyway perspective is critical for understanding how wild birds contribute to the persistence of AIV over large spatial and temporal scales, with implications for how to focus surveillance efforts and identify risks to public health. This study characterized spatio-temporal infection patterns in 10,389 waterfowl at two important locations within the Pacific Flyway--breeding sites in Interior Alaska and wintering sites in California's Central Valley during 2007-2009. Among the dabbling ducks sampled, the northern shoveler (Anas clypeata) had the highest prevalence of AIV at both breeding (32.2%) and wintering (5.2%) locations. This is in contrast to surveillance studies conducted in other flyways that have identified the mallard (Anas platyrhynchos) and northern pintail (Anas acuta) as hosts with the highest prevalence. A higher diversity of AIV subtypes was apparent at wintering (n=42) compared with breeding sites (n=17), with evidence of mixed infections at both locations. Our study suggests that wintering sites may act as an important mixing bowl for transmission among waterfowl in a flyway, creating opportunities for the reassortment of the virus. Our findings shed light on how the dynamics of AIV infection of wild bird populations can vary between the two ends of a migratory flyway.

Vector-Borne and Zoonotic Diseases↗