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At least 919 records · Page 51Linked to original sources

USGS2021

Oral sylvatic plague vaccine does not adequately protect prairie dogs (Cynomys spp.) for endangered black-footed ferret (Mustela nigripes) conservation

The plague bacterium Yersinia pestis is lethal to endangered black-footed ferrets ( Mustela nigripes , BFF) and the prairie dogs ( Cynomys spp., PD) on which they depend for habitat and prey. We assessed the effectiveness of an oral sylvatic plague vaccine delivered in baits to black-tailed PD ( Cynomys ludovicianus , BTPD) from 2013 to 2017 on the Charles M. Russell National Wildlife Refuge (CMR) in northcentral Montana. We permanently marked BTPD on four paired vaccine ( N = 1,349 individuals) and placebo plots ( N = 926; 7,027 total captures). We analyzed capture–recapture data under a Cormack–Jolly–Seber model to estimate annual apparent survival. Overall, survival averaged 0.05 lower on vaccine plots than on paired placebo plots. Immediately before noticeable die-offs and detecting plague on pairs CMR1 and CMR2, 89% of BTPD sampled on vaccine plots had consumed at least one bait and the immune systems (pleural) of 40% were likely boosted by consuming baits over multiple years. Survival to the following year was 0.16 and 0.05 on the vaccine plots and 0.19 and 0.06 on the placebo plots for pairs CMR1 and CMR2, respectively. These rates were markedly lower than 0.63, the overall average estimate on those same plots during the previous 3 years. PD populations subjected to such large die-offs would not be expected to sustain a BFF population. An overriding limitation to achieving sufficient protection rests with vaccine delivery constraints. Late summer/fall bait distribution results in the highest bait uptake rates. However, the PD birth pulse each spring can double the size of populations in most years, greatly reducing the proportion of vaccinates in populations and diminishing potential herd immunity benefits. In addition to nonvaccinated juveniles and PD that do not consume bait, incomplete vaccine protection and time required for immunity to develop leaves a large majority of PD populations vulnerable to plague for 6–7 months or more each year.

Montana↗

USGS1966

A method of shipping live larvae of Simulium vittatum long distances (Diptera: Simuliidae)

During studies on the biology and ecology of black flies (Simuliidae) at the Seney National Wildlife Refuge, Seney, Michigan, and at the Patuxent Wildlife Research Center, Laurel, Maryland, larvae of 3 species of black fly ( Simulium vittatum Zetterstedt, S. aureum Fries, and S. decorum Walker) were collected and transported for distances of up to 50 miles in nonagitated jars of water. In each case the water used to transport the larvae was removed from the waterway where the particular larvae were taken. However, on numerous occasions it was found that larvae could not be kept alive in nonagitated water jars for more than 6 hr.

Annals of the Entomological Society of America↗

USGS1968

Collecting and rearing black flies

This paper, based on a study carried out at the Seney National Wildlife Refuge, Seney, Michigan, and the Patuxent Wildlife Research Center, Laurel, Maryland, describes methods and techniques for collecting, storing, and rearing 8 species of Simuliidae. Included in the study were Cnephia dacotensis (Dyar & Shannon), C. mutata (Malloch), Prosimulium fuscum Syme & Davies, Simulium aureum Fries, S. decorum (Walker), S. venustum Say, S. verecundum Stone & Jamnback, and S. vittattum Zetterstedt. Simuliid eggs collected from a variety of habitats, packed with wet materials in plastic bags and held at 4°C, have remained viable, thus far, up to 424 days. Eggs held at 0° to −70°C failed to hatch when placed in rearing aquariums. Air-dried eggs held at 4°C for 339–535 days failed to hatch after being held in aquariums for 166 days. Immature stages of black flies were successfully reared in 1¼-gallon Pyrex jars and 15-gallon plexiglas aquariums in which the water was agitated by compressed air and aquarium pumps. Water velocities of 0.250–0.542 feet per second were obtained in streams of air bubbles created by use of air stones. Of 21 larval diets used, one consisting of Purina Dog Chow (60-mesh or finer), brain-heart infusion broth, and brewer's yeast powder, and a second consisting of Wayne's dog chow (60-mesh or finer) and brain-heart infusion broth without brewer's yeast powder, were most satisfactory. Larvae were fed 1 gram of diet per 1¼- gallon aquarium and 2 grams per 15-gallon aquarium biweekly. In most of the 225 cultures of S. aureum, S. decorum, S. verecundum, S. venustum, and S. Vittatum it took from 1 to 5 days for the development of eggs to larvae (165 cultures, 73%) and the same number of days for the development of pupae to adults (172 cultures, 76%). Development time for larvae to pupae was fairly closely divided between 11–15 days (63 cultures, 28%) and 16–20 days (53 cultures, 23.6%). The entire period for development from egg to adult after placement of eggs in rearing aquariums was from 21 to 25 days for 26.7% of the cultures.

Annals of the Entomological Society of America↗

USGS1972

The feeding of some ornithophilic black flies (Diptera: Simuliidae) in the laboratory and their role in the transmission of Leucocytozoon simondi

Techniques and equipment are described for feeding, in the laboratory, Cnephia invenusta (Walker), Simulium innocens Shewell, and S. rugglesi Nicholson & Mickel collected from exposed birds at the Seney National Wildlife Refuge, Seney, Michigan, and C. ornithophilia Davies, Peterson, & Wood, S. euryadminiculum Davies, and S. rugglesi reared from larvae at the Seney Refuge ( S. rugglesi ) and the Patuxent Wildlife Research Center, Laurel, Maryland. In 4 feeding experiments with C. invenusta on Pekin ducklings, 109 fed of 194 flies exposed; in 2 experiments with S. innocens on a mallard duckling and an Emden gosling, 35 fed of 65 flies exposed; in 12 experiments with S. rugglesi on mallard ducklings and Canada goose goslings, 465 fed of 1215 flies exposed; in 40 experiments with C. ornithophilia on Khaki Campbell, mallard, and Pekin ducklings and yearling Canada and Emden goslings, 950 fed of 1713 flies exposed; and, in 2 experiments with S. euryadminiculum on Pekin ducklings, 27 fed of 46 flies exposed. Feeding time varied from 2.10 to 15 minutes. C. ornithophilia, S. innocens , and S. rugglesi fed on Khaki Campbell, mallard, and Pekin ducklings and yearling Canada geese infected with Leucocytozoon simondi Mathis & Leger were held 4-7 days after the blood meal. The flies were triturated in physiological saline and deactivated calf serum and inoculated intravenously and intraperitoneally in parasite-free Pekin, Khaki Campbell, and mallard ducklings and Canada goose goslings. Birds became infected with L. simondi 9-14 days after being inoculated with C. ornithophilia ; 4-7 days after being inoculated with S. innocens ; and 9 days after being inoculated with S. rugglesi . Starved, laboratory-fed C. ornithophilia fed first on L. simondi infected Khaki Campbell and Pekin ducklings, held 4-7 days at room temperature, then fed for the 2nd time on parasite-free Pekin ducklings, transmitted the infection by their bite. The birds showed young parasites in the peripheral blood 10 and 11 days following the 2nd feeding.

Annals of the Entomological Society of America↗

USGS2002

Wood Thrush movements and habitat use: Effects of forest management for Red-cockaded Woodpeckers

We monitored adult and juvenile breeding-season movements and habitat use of radio-tagged Wood Thrushes ( Hylocichla mustelina ) at the Piedmont National Wildlife Refuge, central Georgia, USA. We investigated the effects that management for Red-cockaded Woodpeckers ( Picoides borealis ), thinning and burning >30 year old loblolly pine ( Pinus taeda ) habitat, had on Wood Thrushes, a ground-foraging and midstory-nesting species. Adult Wood Thrush pairs regularly moved long distances between nesting attempts (range 1 to 17,388 m). The only experimental effect we found on adult movements was a decrease in weekly emigration rates (Ψ) from thinned and burned compartments after silvicultural management. Adult males preferred riparian hardwoods with sparse to moderate cover and those preferences increased following management. Juveniles remained near their nest site ( x̄ = 177 m, SE = 113) for an average 24 days (SE = 6.3), and then dispersed a mean 2,189 m (SE = 342). Before dispersal, juveniles preferred upland hardwood–pine mixed habitat ( P < 0.05) with moderate overstory cover ( P < 0.05). We found no management effects on dispersal distances or predispersal habitat use. However, juveniles from thinned and burned compartments dispersed to hardwood habitats with dense cover, whereas birds from control compartments dispersed to pine-dominated habitats with sparse cover. All juveniles dispersed to areas with habitat similar to what they used before dispersal. Small-scale thinning and burning for Red-cockaded Woodpeckers may have had little effect on Wood Thrush habitat use and movements because typical movements were often larger than the scale (stand or compartment) targeted for management.

The Auk↗

USGS2021

Management foundations for navigating ecological transformation by resisting, accepting, or directing social-ecological change

Despite striking global change, management to ensure healthy landscapes and sustained natural resources has tended to set objectives on the basis of the historical range of variability in stationary ecosystems. Many social–ecological systems are moving into novel conditions that can result in ecological transformation. We present four foundations to enable a transition to future-oriented conservation and management that increases capacity to manage change. The foundations are to identify plausible social–ecological trajectories, to apply upstream and deliberate engagement and decision-making with stakeholders, to formulate management pathways to desired futures, and to consider a portfolio approach to manage risk and account for multiple preferences across space and time. We use the Kenai National Wildlife Refuge in Alaska as a case study to illustrate how the four foundations address common land management challenges for navigating transformation and deciding when, where, and how to resist, accept, or direct social–ecological change.

Alaska↗

USGS2005

Prevalence of pox-like lesions and malaria in forest bird communitites on leeward Mauna Loa volcano, Hawaii

Introduced avian pox virus and malaria have had devastating impacts on native Hawaiian forest birds, yet little has been published about their prevalence and distribution in forest bird communities outside of windward Hawaii Island. We surveyed native and non-native forest birds for these two diseases at three different elevations on leeward Mauna Loa Volcano at the Kona Forest Unit of Hakalau Forest National Wildlife Refuge. Prevalence of malaria by both serology and microscopy varied by elevation and ranged from 28% at 710 m to 13% at 1830 m. Prevalence of pox-like lesions also varied by altitude, ranging in native species from 10% at 710 m to 2% at 1830 m. Native species at all elevations had the highest prevalence of malarial antibody and pox-like lesions. By contrast, pox-like lesions were not detected in individuals of four non-native species and only 5% of Japanese White-eye ( Zosterops japonicus ) was positive for malaria. A significantly high proportion of birds with pox-like lesions also had serological evidence of concurrent, chronic malarial infections, suggesting an interaction between these diseases, dual transmission of both diseases by the primary mosquito vector ( Culex quinquefasciatus ) or complete recovery of some pox-infected birds without loss of toes. Results from this study document high prevalence of malaria and pox at this refuge. Development of effective disease control strategies will be important for restoration of remnant populations of the endangered ‘Akiapola‘au ( Hemignathus munroi ), Hawaii Creeper ( Oreomystis mana ), and Hawaii ‘Akepa ( Loxops coccineus coccineus ) that still occur on the refuge.

Hawai'i↗

USGS2005

Using the risk-disturbance hypothesis to assess the relative effects of human disturbance and predation risk on foraging American Oystercatchers

The risk-disturbance hypothesis asserts that animals perceive human disturbance similar to nonlethal predation stimuli, and exhibit comparable responses in the form of optimization tradeoffs. However, few studies have examined how natural predation risk factors interact with human-disturbance stimuli to elicit such responses. We observed American Oystercatcher ( Haematopus palliatus ) vigilance behavior from September–December 2002 on the Cape Romain National Wildlife Refuge, South Carolina. A set of models was constructed based on 340 focal-animal samples and models revealed relationships between vigilance behavior, predator density, and boat activity. Oystercatchers increased vigilance in response to aerial predators, particularly late in the season when predator species composition was dominated by Northern Harriers ( Circus cyaneus ). At a broader temporal scale, oystercatchers exhibited the highest vigilance rates during simultaneous peaks in boating disturbance and Osprey ( Pandion haliaetus ) activity. Due to this temporal overlap of stimuli, it is difficult to interpret what may have been driving the observed increased in vigilance. Foraging rates appeared to be primarily driven by habitat and tidal stage indicating that time lost to vigilance did not effectively reduce intake. Taken together, these findings provide some support for the risk-disturbance hypothesis, underscore the sensitivity of disturbance studies to temporal scale, and draw attention to the potential confounding effects of natural predation risk.

South Carolina↗

USGS2014

Predicting connectivity of green turtles at Palmyra Atoll, central Pacific: a focus on mtDNA and dispersal modelling

Population connectivity and spatial distribution are fundamentally related to ecology, evolution and behaviour. Here, we combined powerful genetic analysis with simulations of particle dispersal in a high-resolution ocean circulation model to investigate the distribution of green turtles foraging at the remote Palmyra Atoll National Wildlife Refuge, central Pacific. We analysed mitochondrial sequences from turtles ( n = 349) collected there over 5 years (2008–2012). Genetic analysis assigned natal origins almost exclusively (approx. 97%) to the West Central and South Central Pacific combined Regional Management Units. Further, our modelling results indicated that turtles could potentially drift from rookeries to Palmyra Atoll via surface currents along a near-Equatorial swathe traversing the Pacific. Comparing findings from genetics and modelling highlighted the complex impacts of ocean currents and behaviour on natal origins. Although the Palmyra feeding ground was highly differentiated genetically from others in the Indo-Pacific, there was no significant differentiation among years, sexes or stage-classes at the Refuge. Understanding the distribution of this foraging population advances knowledge of green turtles and contributes to effective conservation planning for this threatened species.

Journal of the Royal Society Interface↗

USGS2023

The unmarked R package: Twelve years of advances in occurrence and abundance modelling in ecology

Species distribution models (SDMs) are widely applied to understand the processes governing spatial and temporal variation in species abundance and distribution but often do not account for measurement errors such as false negatives and false positives. We describe unmarked , a package for the freely available and open-source R software that provides a complete workflow for modelling species distribution and abundance while explicitly accounting for measurement errors. Here we focus on recent advances in unmarked functionality to support multi-species, multi-state, and multi-season data, as well as support for fitting models with random effects. For illustration, we present an analysis of Acadian Flycatcher Empidonax virescens abundance on Roanoke River National Wildlife Refuge, North Carolina, USA, over 18 years. We found that Acadian Flycatcher abundance was initially greater in hardwood plantation habitat relative to bottomland hardwood forest along river levees but that abundance declined over time in both habitats. We plan for unmarked development to keep pace with advances in hierarchical modelling in ecology, including better handling of continuous-time data from camera trap and automated recording units and integrated models for multiple data streams.

Methods in Ecology & Evolution↗

USGS2013

Importance of the National Petroleum Reserve-Alaska for aquatic birds

We used data from aerial surveys (1992–2010) of >100,000 km 2 and ground surveys (1998–2004) of >150 km 2 to estimate the density and abundance of birds on the North Slope of Alaska (U.S.A.). In the ground surveys, we used double sampling to estimate detection ratios. We used the aerial survey data to compare densities of birds and Arctic fox (Vulpes lagopus), the major nest predator of birds, on the North Slope, in Prudhoe Bay, and in nearby areas. We partitioned the Prudhoe Bay oil field into 2 × 2 km plots and determined the relation between density of aquatic birds and density of roads, buildings, and other infrastructure in these plots. Abundance and density (birds per square kilometer) of 3 groups of aquatic birds—waterfowl, loons, and grebes; shorebirds; and gulls, terns, and jaegers—were highest in the National Petroleum Reserve–Alaska (NPRA) and lowest in the Arctic National Wildlife Refuge. Six other major wetlands occur in the Arctic regions of Canada and Russia, but the largest population of aquatic birds was in the NPRA. Aquatic birds were concentrated in the northern part of the NPRA. For example, an area that covered 18% of the NPRA included 53% of its aquatic birds. The aerial surveys showed that bird density was not lower and fox density was not higher in Prudhoe Bay than in surrounding areas. Density of infrastructure did not significantly affect bird density for any group of species. Our results establish that the NPRA is one of the most important areas for aquatic birds in the Arctic. Our results and those of others also indicate that oil production, as practiced in Prudhoe Bay, does not necessarily lead to substantial declines in bird density or productivity in or near the developed areas.

Alaska↗

USGS2024

Modeling the response of an endangered rabbit population to RHDV2 and vaccination

Rabbit hemorrhagic disease virus 2 (RHDV2), recently detected in the western United States, has the potential to cause mass mortality events in wild rabbit and hare populations. Currently, few management strategies exist other than vaccination. We developed a spatially explicit model of RHDV2 for a population of riparian brush rabbits ( Sylvilagus bachmani riparius ), a subspecies of brush rabbit classified as endangered in the United States, on a subsection of the San Joaquin River National Wildlife Refuge. The goal of our model was to provide guidance regarding vaccination strategies for an endangered rabbit species. Our model predicts that increased interactions between rabbits (a proxy for landscape connectivity) and disease transmission rates among susceptible hosts (individual brush rabbits and conspecifics) have the greatest influence on the outcome of a potential vaccination campaign. Our model projects that across a range of parameter estimates (given an RHDV2 incursion), the median estimated population size with a 0%–10% vaccination rate after 1 year is 538 rabbits (95% Confidence Interval [C.I.] 69–1235), approximately 36% of the expected size of the study population of 1470 rabbits without an RHDV2 introduction. With a 10%–20%, 20%–30%, or 30%–40% vaccination rate, the median estimated population size increased to 628 rabbits (95% C.I. 130–1298), 723 rabbits (95% C.I. 198–1317), and 774 rabbits (95% C.I. 228–1410), respectively. These estimates represent 43%, 49%, and 53% of the expected population size without an RHDV2 introduction. Overall, a 1% increase in vaccination rate was associated with a six rabbit (95% C.I. 5–7) increase in total remaining population size. This result is dependent on assumptions regarding environmental transmission, home range size (and contact rates of rabbits). Given the relatively short lifespan of rabbits and the potential need for boosters, vaccination programs are most likely to be successful for small target populations where relatively high vaccination rates can be maintained.

California↗

USGS2025

Getting ahead of the crises: Developing an avian malaria disease management plan for Hawaiian forest birds

Avian malaria is an existential threat to a majority of native Hawaiian forest birds. Climate change is facilitating the spread of malaria to historically disease-free areas, and despite the risk of native Hawaiian forest bird extinctions from malaria outbreaks, no comprehensive disease management plans exist for forest bird conservation areas. Hakalau Forest National Wildlife Refuge, Hawai‘i, supports a thriving bird community in a historically disease-free area that is now vulnerable to malaria incursion. Drawing on the expertise of land managers and research scientists, we developed an approach that could be used to proactively address the risk of expanding malaria into the Refuge. The plan lays out a multi-level approach that includes options for monitoring and management actions depending on defined threat levels: Vigilant, High Alert, Disease Outbreak, and Crisis levels. Initial Vigilant and High Alert levels monitor bird populations, climate conditions, and mosquito occurrence for signs of possible disease outbreaks, with higher levels shifting toward more direct management responses. While specific actions will change as new tools become available, the proactive approach can help Refuge managers better respond to changing malaria levels in the future and provide a model for managing disease here in Hawai‘i and elsewhere.

Hawaii↗

USGS2018

Predicting effects of large-scale reforestation on native and exotic birds

Aim Ecological restoration is critical for recovering biodiversity and ecosystem services, yet designing interventions to achieve particular outcomes remains fraught with challenges. In the extensive regions where non-native species are firmly established, it is unlikely that historical conditions can be fully reinstated. To what degree, and how rapidly, can human-dominated areas be shifted via restoration into regimes that benefit target species, communities or processes? Location We explore this question in a >20-year-old reforestation effort underway at Hakalau Forest National Wildlife Refuge in montane Hawaii. This large-scale planting of Acacia koa trees is designed to secure populations of globally threatened bird species by transitioning the site rapidly from pasture to native forest. Methods We surveyed all forest birds in multiple corridors of young planted trees, remnant corridors of mature trees along gulches and at sites within mature forest. Using a Bayesian hierarchical approach, we identified which factors (distance from forest, habitat type and surrounding tree cover) had the most important influence on native and exotic bird abundance in the reforestation area. Results We found that 90% of native and exotic bird species responded quickly, occupying corridors of native trees approximately a decade after planting. However, native and exotic forest birds responded to markedly different characteristics of the reforested area. Native bird abundance was strongly predicted by proximity to mature forest and remnant corridors; conversely, exotic bird abundance was best predicted by overall tree cover throughout the area reforested. Main conclusions Our results demonstrate that large-scale tree planting in corridors adjacent to mature forest can catalyse rapid recovery (both increased abundance and expanded distribution) of forest birds and that it is possible to design reforestation to benefit native species in novel ecosystems.

Hawaii↗

USGS2023

Borealization of nearshore fishes on an interior Arctic shelf over multiple decades

Borealization is a type of community reorganization where Arctic specialists are replaced by species with more boreal distributions in response to climatic warming. The process of borealization is often exemplified by the northward range expansions and subsequent proliferation of boreal species on the Pacific and Atlantic inflow Arctic shelves (i.e., Bering/Chukchi and Barents seas, respectively). But the circumpolar nearshore distribution of Arctic-boreal fishes that predates recent warming suggests borealization is possible beyond inflow shelves. To examine this question, we revisited two nearshore lagoons in the eastern Alaska Beaufort Sea (Kaktovik and Jago lagoons, Arctic National Wildlife Refuge, Alaska, USA), a High Arctic interior shelf. We compared summer fish species assemblage, catch rate, and size distribution among three periods that spanned a 30-year record (baseline conditions, 1988–1991; moderate sea ice decline, 2003–2005; rapid sea ice decline, 2017–2019). Fish assemblages differed among periods in both lagoons, consistent with borealization. Among Arctic specialists, a clear decline in fourhorn sculpin ( Myoxocephalus quadricornis , Kanayuq in Iñupiaq) occurred in both lagoons with 86%–90% lower catch rates compared with the baseline period. Among the Arctic-boreal species, a dramatic 18- to 19-fold increase in saffron cod ( Eleginus gracilis , Uugaq) occurred in both lagoons. Fish size (length) distributions demonstrated increases in the proportion of larger fish for most species examined, consistent with increasing survival and addition of age-classes. These field data illustrate borealization of an Arctic nearshore fish community during a period of rapid warming. Our results agree with predictions that Arctic-boreal fishes (e.g., saffron cod) are well positioned to exploit the changing Arctic ecosystem. Another Arctic-boreal species, Dolly Varden ( Salvelinus malma , Iqalukpik), appear to have already responded to warming by shifting from Arctic nearshore to shelf waters. More broadly, our findings suggest that areas of borealization could be widespread in the circumpolar nearshore.

Alaska↗

USGS2025

Reducing bias in shorebird nest survival rates across a large Arctic landscape

Reproductive success is a key demographic parameter that can have profound impacts on a species' population trend. Indeed, poor reproductive success has been suggested as a contributing factor to the declines observed in many species of birds, including Arctic-breeding shorebirds. However, the available information on Arctic-breeding shorebird nest survival is restricted to a limited number of non-random locations where proximity to human settlements and traditional invasive monitoring techniques may artificially alter nest predation rates and, thus, bias results. To accurately assess reproductive success, unbiased estimates are needed. In this study, we monitored 96 shorebird nests (six species) at 41 randomly selected sites across a large Arctic landscape (1219 km 2 area of the Arctic National Wildlife Refuge) using minimally invasive techniques (i.e. single nest visits, temperature loggers and cameras) in 2019 and 2022. Overall, daily survival was 0.975 (95% CI: 0.955–0.987), which translates to a 53% (95% CI: 32–72%) probability of a shorebird nest surviving the median (25 days) incubation period for the studied species. Camera footage indicated Arctic Foxes Vulpes lagopus were the primary nest predator (85% of identified predation events), but Parasitic Jaegers Stercorarius parasiticus and Sandhill Cranes Grus canadensis also contributed to nest loss. In both years, greater nest failure occurred in the northwest and northcentral regions of our study area, potentially the result of greater shorebird abundance and density-dependent predation rates. Nest survival rates obtained in this study were the same as those obtained in a previous large geographical study that monitored shorebird nests across numerous small, non-randomly selected, high-density shorebird field sites that employed intensive human monitoring techniques. However, site-specific and annual differences in predator and shorebird species and densities make direct comparisons to previous studies difficult. Continued monitoring using methods that minimize bias and are consistent across time are needed to accurately measure true changes in nest survival rates that may occur under a changing climate and with increased human development.

Alaska↗

USGS2003

Experimental manipulations of snow-depth: Effects on nutrient content of caribou forage

We investigated the potential effects of global climate change on arctic tundra vegetation used as caribou forage. A total of 96 experimental plots was established at six sites on the coastal plain of the Arctic National Wildlife Refuge, Alaska, in 1993 and 1994. We erected snow-fences to increase the amount of snow deposition, and therefore delay the date of the snowmelt on 48 plots (referred to as increased snow/late melting plots). We used black mesh netting on the surface of the snow to increase the rate of melting on 24 plots; the remaining 24 plots served as controls. In July 1994, we collected green leaves from Eriophorum vaginatum, Salix planifolia, and Betula nana and analysed these samples for total carbon and total nitrogen content. Ratios of carbon to nitrogen differed among treatments for all three species. Generally, C:N ratios for B. nana and E. vaginatum on increased snow/late melting plots were lower than on control plots. C:N ratios for S. planifolia on increased snow/late melting plots did not differ from controls, but were lower than on plots which started to melt early. These results may be due to the timing of nitrogen translocation from leaf and stem tissue into storage organs, or due to an increase in available nitrogen input to the system. Further sampling is needed to adequately determine the mechanism responsible for increased nitrogen content of caribou forage in areas with increased amount of snow and delayed snowmelt. ?? 1997 Blackwell Science Ltd.

Global Change Biology↗

USGS2012

Changes in avian and plant communities of aspen woodlands over 12 years after livestock removal in the northwestern Great Basin

Riparian and quaking aspen (Populus tremuloides) woodlands are centers of avian abundance and diversity in the western United States, but they have been affected adversely by land use practices, particularly livestock grazing. In 1990, cattle were removed from a 112,500-ha national wildlife refuge in southeastern Oregon. Thereafter, we monitored changes in vegetation and bird abundance in years 1–3 (phase 1) and 10–12 (phase 2) in 17 riparian and 9 snow-pocket aspen plots. On each 1.5-ha plot, we sampled vegetation in 6 transects. Three times during each breeding season, observers recorded all birds 50 m to each side of the plot's 150-m centerline for 25 minutes. We analyzed data with multivariate analysis of variance and paired t tests with p values adjusted for multiple comparisons. In both periods, riparian and snow-pocket aspen produced extensive regeneration of new shoots (x̄ = 2646 stems/ha and 7079 stems/ha, respectively). By phase 2, a 64% increase in medium-diameter trees in riparian stands indicated successful recruitment into the overstory, but this pattern was not seen in snow-pocket stands, where the density of trees was over 2 times greater. By phase 2 in riparian and snow-pocket stands, native forb cover had increased by 68% and 57%, respectively, mesic shrub cover had increased by 29% and 58%, and sagebrush cover had decreased by 24% and 31%. Total avian abundance increased by 33% and 39% in riparian and snow-pocket aspen, respectively, ground or understory nesters increased by 133% and 67% and overstory nesters increased by 34% and 33%. Similarly, ground or understory foragers increased by 25% and 32%, aerial foragers by 55% and 57%, and overstory foragers by 66% and 43%. We interpreted the substantial regeneration of aspen shoots, increased densities of riparian forbs and shrubs, and increased avian abundances as a multitrophic-level response to the total removal of livestock and as substantial movement toward recovery of biological integrity.

Aspen Woodlands;Great Basin↗