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At least 1,045 records · Page 58Linked to original sources
USGS2018

Making do with less: Must sparse data preclude informed harvest strategies for European waterbirds?

The demography of many European waterbirds is not well understood because most countries have conducted little monitoring and assessment, and coordination among countries on waterbird management has little precedent. Yet intergovernmental treaties now mandate the use of sustainable, adaptive harvest strategies, whose development is challenged by a paucity of demographic information. In this study, we explore how a combination of allometric relationships, fragmentary monitoring and research information, and expert judgment can be used to estimate the parameters of a theta-logistic population model, which in turn can be used in a Markov decision process to derive optimal harvesting strategies. We show how to account for considerable parametric uncertainty, as well as for different management objectives. We illustrate our methodology with a poorly understood population of taiga bean geese ( Anser fabalis fabalis ), which is a popular game bird in Fennoscandia. Our results for taiga bean geese suggest that they may have demographic rates similar to other, well-studied species of geese, and our model-based predictions of population size are consistent with the limited monitoring information available. Importantly, we found that by using a Markov decision process, a simple scalar population model may be sufficient to guide harvest management of this species, even if its demography is age-structured. Finally, we demonstrated how two different management objectives can lead to very different optimal harvesting strategies, and how conflicting objectives may be traded off with each other. This approach will have broad application for European waterbirds by providing preliminary estimates of key demographic parameters, by providing insights into the monitoring and research activities needed to corroborate those estimates, and by producing harvest management strategies that are optimal with respect to the managers’ objectives, options, and available demographic information.

Ecological Applications↗
USGS1998

An individual-based, spatially-explicit simulation model of the population dynamics of the endangered red-cockaded woodpecker, Picoides borealis

Spatially-explicit population models allow a link between demography and the landscape. We developed a spatially-explicit simulation model for the red-cockaded woodpecker, Picoides borealis , an endangered and territorial cooperative breeder endemic to the southeastern United States. This kind of model is especially appropriate for this species because it can incorporate the spatial constraints on dispersal of helpers, and because territory locations are predictable. The model combines demographic data from a long-term study with a description of the spatial location of territories. Sensitivity analysis of demographic parameters revealed that population stability was most sensitive to changes in female breeder mortality, mortality of female dispersers and the number of fledglings produced per brood. Population behavior was insensitive to initial stage distribution; reducing the initial number of birds by one-half had a negligible effect. Most importantly, we found that the spatial distribution of territories had as strong an effect on response to demographic stochasticity as territory number. Populations were stable when territories were highly aggregated, with as few as 49 territories. When territories were highly dispersed, more than 169 territories were required to achieve stability. Model results indicate the importance of considering the spatial distribution of territories in management plans, and suggest that this approach is worthy of further development.

North Carolina↗
USGS1997

Seasonal and annual survival of adult Pacific brant

Declining mid-winter counts of Pacific brant ( Branta bernicla nigricans ) and reduced numbers of nesting birds on their main breeding grounds prompted us to assess factors that may be limiting recovery of this population. We estimated seasonal and annual survival rates of adult brant in 1986-93 from resightings of leg-banded birds. Brant were banded at a major colony on the Yukon-Kuskokwim Delta, Alaska (Y-K Delta) in 1986-92, and resighted there in 1987-93 as well as at major fall and spring migration and wintering areas in 1990-93. Seasonal survival was the same for males and females. Mean monthly survival rate was lowest (P ≤ 0.05) in late spring migration (15 Apr-1 Jun), the period of greatest subsistence harvest on the breeding grounds, and highest in winter (1 Jan-1 Mar), the period of greatest sport harvest. Annual survival rate did not vary among years (F = 0.51; 5, 718 df; P = 0.91) and averaged 0.840 (SE = 0.031) from 1986 to 1993. Subsistence harvest has contributed to low population levels of Pacific brant.

Alaska↗
USGS2009

Filling a void: abundance estimation of North American populations of arctic geese using hunter recoveries

We consider use of recoveries of marked birds harvested by hunters, in conjunction with continental harvest estimates, for drawing inferences about continental abundance of a select number of goose species. We review assumptions of this method, a version of the Lincoln?Petersen approach, and consider its utility as a tool for making decisions about harvest management in comparison to current sources of information. Finally, we compare such estimates with existing count data, photographic estimates, or other abundance estimates. In most cases, Lincoln estimates are far higher than abundances assumed or perhaps accepted by many waterfowl biologists and managers. Nevertheless, depending on the geographic scope of inference, we suggest that this approach for abundance estimation of arctic geese may have usefulness for retrospective purposes or to assist with harvest management decisions for some species. Lincoln?s estimates may be as close or closer to truth than count, index, or photo data, and can be used with marking efforts currently in place for estimation of survival and harvest rates. Although there are bias issues associated with estimates of both harvest and harvest rate, some of the latter can be addressed with proper allocation of marks to spatially structured populations if subpopulations show heterogeneity in harvest rates.

Book chapter↗
USGS2021

American Woodcock singing-ground survey: Comparison of four models for trend in population size

Wildlife biologists monitor the status and trends of American woodcock Scolopax minor populations in the eastern and central United States and Canada via a singing-ground survey, conducted just after sunset along roadsides in spring. Annual analyses of the survey produce estimates of trend and annual indexes of abundance for 25 states and provinces, management regions, and survey-wide. In recent years, researchers have used a log-linear hierarchical model that defines year effects as random effects in the context of a slope parameter (the S model) to model population change. Recently, researchers have proposed alternative models suitable for analysis of singing-ground survey data. Analysis of a similar roadside survey, the North American Breeding Bird Survey, has indicated that alternative models are preferable for almost all species analyzed in the Breeding Bird Survey. Here, we use leave-one-out cross-validation to compare model fit for the present singing-ground survey model to fits of three alternative models, including a model that describes population change as the difference in expected counts between successive years (the D model) and two models that include t -distributed extra-Poisson overdispersion effects (H models) as opposed to normally distributed extra-Poisson overdispersion. Leave-one-out cross-validation results indicate that the Bayesian predictive information criterion favored the D model, but a pairwise t -test indicated that the D model was not significantly better-fitting to singing-ground survey data than the S model. The H models are not preferable to the alternatives with normally distributed overdispersion. All models provided generally similar estimates of trend and annual indexes suggesting that, within this model set, choice of model will not lead to alternative conclusions regarding population change. However, as in Breeding Bird Survey analyses, we note a tendency for S model results to provide slightly more extreme estimates of trend relative to D models. We recommend use of the D model for future singing-ground survey analyses.

Eastern and Central United States and Canada↗
USGS2024

Effects of insecticide spray drift on arthropod prey resources of birds in grasslands in Minnesota

Soybean aphid ( Aphis glycines ) insecticides are used throughout the Upper Midwest and Great Plains regions of North America, including the farmland region of Minnesota, USA, to combat insect pests. These broad-spectrum, foliar spray insecticides have the potential to drift beyond target fields into nearby grassland cover where birds and other insectivores forage. Arthropods serve important roles in grassland ecology and are susceptible to mortality and sublethal effects from exposure to these pesticides. Our objective was to assess effects of soybean aphid insecticides on grassland arthropods, especially those that are important in grassland bird diets. We measured the abundance, consumable biomass, and family richness of insects and spiders in grasslands adjacent to soybean fields in an agricultural landscape. Soybean fields were treated with chlorpyrifos and lambda-cyhalothrin, which were the 2 most common foliar pesticides used to control soybean aphids in Minnesota. We compared measures at focal sites to samples collected at reference sites adjacent to corn fields not sprayed for aphids during 3 periods in mid-to-late summer: 1–3 days before spraying, 3–5 days post-spraying, and 19–21 days post-spraying. The abundance of arthropods in focal grasslands was lower 3–5 days after pesticide applications. Coleoptera family richness at focal sites was also lower than at reference sites 3–5 days after pesticide applications. These measures 19–21 days after application were similar to pre-spraying levels, indicating that arthropod populations rebounded during this period. Measures of consumable dry biomass, bird prey abundance, bird prey biomass, family richness of Araneae, family richness of Hemiptera, and family richness of Orthoptera were not different between focal and reference sites after spraying. Our results reveal that reductions in arthropod food abundance for grassland birds are associated with pesticide applications up to 5 days after spraying. We suggest that natural resource managers factor proximity to row crop fields and susceptibility to pesticide drift into decisions about where to add grassland cover to landscapes.

Minnesota↗
USGS1989

Annual survival rates of breeding adult roseate terns

Analyses of the capture-recapture data on 910 individual Roseate Terns ( Sterna dougallii ) trapped from 1978-1987 as breeding adults on nests on Falkner Island, Connecticut, estimate the average annual minimum adult survival rate to be 0.74-0.75. There was weak evidence of year-to-year variation in annual survival rates during the study period. The Jolly-Seber models used to estimate survival rates also generated estimates of population size and capture probabilities. To determine the relative importance of adult mortality and permanent emigration in contributing to the estimated annual loss of one-fourth of the breeding population will require further study of intercolony movement between all the major colony sites. Assuming that the loss of birds from the Falkner Island colony site is due mostly to mortality rather than permanent emigration, and that the survival rate of this breeding population is typical of the entire North Atlantic breeding population, then the survival rate of this endangered species is low in comparison to the survival rates of several other marine bird species in the orders Procellariiformes, Pelecaniformes, and Charadriiformes.

The Auk↗
USGS2009

Estimation of avian population sizes and species richness across a boreal landscape in Alaska

We studied the distribution of birds breeding within five ecological landforms in Yukon-Charley Rivers National Preserve, a 10,194-km 2 roadless conservation unit on the Alaska-Canada border in the boreal forest zone. Passerines dominated the avifauna numerically, comprising 97% of individuals surveyed but less than half of the 115 species recorded in the Preserve. We used distance-sampling and discrete-removal models to estimate detection probabilities, densities, and population sizes across the Preserve for 23 species of migrant passerines and five species of resident passerines. Yellow-rumped Warblers (Dendroica coronata) and Dark-eyed Juncos (Junco hyemalis) were the most abundant species, together accounting for 41% of the migrant passerine populations estimated. White-winged Crossbills (Loxia leucoptera), Boreal Chickadees (Poecile hudsonica), and Gray Jays (Perisoreus canadensis) were the most abundant residents. Species richness was greatest in the Floodplain/Terrace landform flanking the Yukon River but densities were highest in the Subalpine landform. Species composition was related to past glacial history and current physiography of the region and differed notably from other areas of the northwestern boreal forest. Point-transect surveys, augmented with auxiliary observations, were well suited to sampling the largely passerine avifauna across this rugged landscape and could be used across the boreal forest region to monitor changes in northern bird distribution and abundance. ?? 2009 The Wilson Ornithological Society.

Wilson Journal of Ornithology↗
USGS2005

Evaluation of current population indices for band-tailed pigeons

There is no formal population survey specifically designed to index population abundance of band-tailed pigeons ( Patagioenas fasciata ) throughout their range. Data from the Breeding Bird Survey (BBS), Washington and Oregon Mineral-Site (WAORMS) surveys, and Washington Call Count (WACC) survey offer evidence of long-term population decline. We investigated the potential to augment BBS, WACC, and WAORMS surveys to provide more precise population indices for the Pacific Coast band-tailed pigeon ( P. f. monilis ) and augment the BBS to index the Interior or “Four Corners” population ( P. f. fasciata ). We calculated statistical power, the probability of detecting population change given that a change exists, and analyzed survey data to investigate the effect of route length, survey repetition, and sample size. Sample sizes of 50 sites or routes yielded corresponding powers of 99% for WAORMS, 54% for WACC, and 30% for Pacific BBS, to detect a 10% annual change over a 5-year period (a = 0.10). Route length and repetition of surveys had little impact on power. Mineral-site surveys provide the greatest potential to monitor breeding populations and detect short-term trends in the Pacific Coast population. New survey techniques are needed for the Interior band-tailed pigeon.

Wildlife Society Bulletin↗
USGS1997

Survival of hatchery-reared lake trout stocked near shore and off shore in Lake Ontario

Establishing a stock of mature, hatchery-reared fish is necessary to restore a self-sustaining population of lake trout Salvelinus namaycush in Lake Ontario. Stocking fish off shore rather than near shore to reduce predation on these fish by large lake trout or piscivorous birds may enhance survival of hatchery-reared fish and accelerate establishment of a population of adults. Results of an earlier study did not support routinely stocking fish off shore by helicopter in Lake Ontario, but stresses associated with helicopter stocking suggested another method of transporting fish off shore might enhance survival. I conducted this study to determine whether stocking lake trout off shore by barge would enhance first-year survival. Two lots of yearling lake trout were stocked at each of four locations in Lake Ontario in May 1992. One lot was stocked from shore, and an identical lot was transported by barge 3.4–10.4 km off shore of nearshore locations and stocked in water 46–52 m deep. Fish were recovered during trawl, gillnet, and creel surveys in 1992–1996. First-year survival of lake trout stocked off shore tended to be better than that of fish stocked near shore. Predation by double-crested cormorants Phalacrocorax auritus likely affected survival of fish stocked near shore at two locations, 7 and 37 km, respectively, from a nesting colony of 5,443 pairs of double-crested cormorants. Predation by large lake trout remains a viable hypothesis, which explains, at least partially, lower survival of lake trout stocked near shore at two other locations. Stocking lake trout off shore of traditional nearshore stocking sites likely will enhance first-year survival of hatchery-reared fish and promote accumulation of an adult population, especially for those occassions where nearshore stocking locations are near nesting colonies of double-crested cormorants.

North American Journal of Fisheries Management↗
USGS1995

Northern Pintail ( Anas acuta )

The Northern Pintail is a medium-sized dabbling duck of slender, elegant lines and conservative plumage coloration. It is circumpolar in distribution and abundant in North America, with core nesting habitat in Alaska and the Prairie Pothole Region of southern Canada and the northern Great Plains. Breeders favor shallow wetlands interspersed throughout prairie grasslands or arctic tundra. An early fall migrant, the species arrives on wintering areas beginning in August, after wing molt, often forming large roosting and feeding flocks on open, shallow wetlands and flooded agricultural fields. The birds consume grains, marsh plant seeds, and aquatic invertebrates throughout the fall and winter. Northern Pintails are among the earliest nesting ducks in North America, beginning shortly after ice-out in many northern areas. Individuals form new pair bonds each winter but are highly promiscuous during the nesting season, with mated and unmated males often involved in vigorous, acrobatic Pursuit Flights. Annual nest success and productivity vary with water conditions, predation, and weather. Females build nests on the ground, often long distances from water. Only the female incubates; her mate leaves shortly after incubation begins. Ducklings hatch together in one day, follow the female to water after a day in the nest, and fledge by July or August. Adults and ducklings consume mainly aquatic invertebrates during the breeding season. Predators and farming operations destroy many thousands of Northern Pintail nests annually; farming has also greatly reduced the amount of quality nesting cover available. Winter habitats are threatened by water shortages, agricultural development, contamination, and urbanization. Periods of extended drought in prairie nesting regions have caused dramatic population declines, usually followed by periods of recovery. Over the long term, however, the continental population of Northern Pintails has declined significantly from 6 million birds in the early 1970s to less than 3 million in the late 1980s and early 1990s. However, new conservation measures, such as habitat restoration and enhancement of agricultural lands, as well as prudent harvest restrictions, suggest that Northern Pintails should have a secure future in North America.

Book chapter↗
USGS2002

Availability of food resources, distribution of invasive species, and conservation of a Hawaiian bird along a gradient of elevation

Aim: We evaluated how an elevation gradient affects: (1) the availability of food required by a specialist seed-eater, Loxioides bailleui Oustalet (Drepanidinae), or pallia, and hence the distribution of this endangered Hawaiian bird, and (2) the distribution of alien threats to Loxioides populations, their primary foods, and their dry-forest habitat, and hence strategies for their conservation. Location: We worked throughout the subalpine forest that encircles Mauna Kea Volcano, Hawai'i Island, but we focused our studies mainly on the western slope between 2000 and 3000 m elevation, where the gradient of elevation was greatest and palila were most abundant. Methods: We determined phenology and productivity patterns of the endemic dry-forest tree species, Sophora chrysophylla (Salisb.) Seem. (Fabaceae), or ma??mane, which provides Loxioides with most of their food, and another common endemic tree, Myoporum sandwicense A. Gray (Myoporaceae), or naio, which provides some resources, along a 786-m elevation gradient at monthly intervals for 10 years (Sophora only). We also determined the availability each month of moth larvae (Lepidoptera) for that were important in the diet of nestling and adult palila. In addition, we documented the incidence of parasitism on moth larvae by several wasp (Hymenoptera) and fly (Diptera) species, and we determined the distribution of predatory wasps and ants (Hymenoptera), which potentially threaten insect prey of birds. Percentage cover of alien grass species that pose fire threats in palila habitat and other weeds were assessed during one survey. Small mammal abundance and distribution were determined by trapping during three (rodent) or five (carnivore) surveys. Results: Sophora flower and seed (pod) availability varied predictably along the elevation gradient, with about 4 months separating peaks in reproduction at high and low elevations. This, together with highly variable production of flowers and pods within elevation strata, resulted in Sophora resources being available to Loxioides throughout the year on the western slope of Mauna Kea. Sophora produced flowers and pods more seasonally where gradients of elevation were short; thus, resources were available less consistently. In contrast, Myoporum produced flowers and fruits with little variation with respect to season or elevation. The availability of important insect prey of Loxioides was also related to elevation, in part because threats to Lepidoptera larvae from parasitic wasps were generally less at higher elevations. Threats to insect prey from predatory ants was also less at higher elevations but the abundance of predatory wasps was not related to elevation. Several weeds that pose the most serious threats to Loxioides habitat were more abundant at mid and low elevations, and alien grass cover was somewhat greater at mid elevation, thereby increasing fire risks in the centre of Loxioides habitat. Predatory mammals, in particular Felis catus Linnaeus, were common throughout the subalpine forest of Mauna Kea. However, Rattus rattus Linnaeus was rare, especially at higher elevations, whereas Mus musculus Linnaeus was more abundant at lower elevations. Main conclusions: Loxioides are concentrated in habitat that is distributed along a substantial gradient of elevation at least in part because food is available throughout the year and threats to food resources are less concentrated. To recover Loxioides elsewhere in its former range, habitats must be restored and alien threats reduced along extensive elevation gradients. Conservation along environmental gradients will likely benefit other Hawaiian birds that track the availability of food across landscapes or that have been stranded in the higher portions of their original ranges because of the greater impacts of alien diseases, predators, food competitors, and habitat stressors at lower elevations.

Journal of Biogeography↗
USGS1995

Hawaii's endemic birds

The endemic landbirds of Hawaii, particularly the Hawaiian honeycreepers, an endemic subfamily of the cardueline finches, are one of the world's most dramatic examples of adaptive radiation and speciation (see glossary) in island ecosystems (Freed et al. 1987; Scott et al. 1988). From what is believed to have been a single successful colonization of the Hawaiian Archipelago by an ancestral species from North America, the honeycreepers evolved into a diverse array of species and subspecies of birds with bills ranging from thick, seed-eating beaks of the palila ( Loxioides bailleui ), to small insectivorous bills as seen on the `amakihi ( Hemignathus virens ), woodpecker-like adaptations of the `akiapola`au ( H. munroi ), and large, decurved nectar-feeding bills of the `i`iwi ( Vestiaria coccinea ). In addition to the honeycreepers, the historically documented endemic Hawaiian avifauna included three seabirds, several waterfowl, two raptors, and perching birds that include a species of crow, and representatives of Old World flycatchers, honeyeaters, and thrushes. In all, at least 71 endemic species and subspecies of Hawaiian birds existed at the time of Captain Cook's arrival in the Hawaiian Islands in 1778. Now, however, 76% of the Hawaiian birds are either extinct or endangered, and several of the remaining unlisted species are showing significant population declines. The arrival of humans to the Hawaiian Islands--starting with the Polynesians more than 1,500 years ago and continuing following European contact--drastically changed many natural ecosystems, leading not only to the extinction of many plant and animal species, but also to a significant reduction in both range and abundance for many other taxa. Originally, the Hawaiian birds were found in all habitat zones on each island, but today few native forest birds are found below 610-m (2,000-ft) elevation, and many of the wetland areas that once provided abundant habitat for waterbirds have been destroyed. Of the historically documented 71 taxa of endemic Hawaiian birds, 23 are now extinct, and 30 of the remaining 48 species and subspecies are listed as endangered or threatened by the U.S. Fish and Wildlife Service (USFWS 1992), many with few or only single populations remaining (Fig. 1; Table 1; Table 2). Studies of recently discovered fossil bird bones have further identified nearly 40 additional species of Hawaiian birds never seen alive by the post-Cook naturalists; many of these became extinct after the Polynesians arrived (Olson and James 1982; H. James, Smithsonian Institution, personal communication).

Hawai'i↗
USGS2016

Environmental factors influence lesser scaup migration chronology and population monitoring

Identifying environmental metrics specific to lesser scaup ( Aythya affinis ; scaup) spring migration chronology may help inform development of conservation, management and population monitoring. Our objective was to determine how environmental conditions influence spring migration of lesser scaup to assess the effectiveness of the Waterfowl Breeding Population and Habitat Survey in accurately estimating scaup populations. We first compared peak timing of mallard ( Anas platyrhynchos ) and scaup migration from weekly ground surveys in North Dakota, USA because the Waterfowl Breeding Population and Habitat Survey is designed to capture annual mallard migration. As predicted, we detected that peak timing of scaup and mallard migrations differed in 25 of 36 years investigated (1980–2010). We marked scaup with satellite transmitters ( n = 78; 7,403 locations) at Long Point, Lake Erie, Ontario, Canada; Pool 19 of the Mississippi River, Iowa and Illinois, USA; and Presque Isle Bay, Lake Erie, Pennsylvania, USA. We tested the assumption that our marked scaup were representative of the continental population using the traditional survey area by comparing timing of migration of marked birds and scaup counted in the North Dakota Game and Fish Department survey. We detected a strong positive correlation between marked scaup and the survey data, which indicated that marked scaup were representative of the population. We subsequently used our validated sample of marked scaup to investigate the effects of annual variation in temperature, precipitation, and ice cover on spring migration chronology in the traditional and eastern survey areas of the Waterfowl Breeding Population and Habitat Survey, 2005–2010. We evaluated competing environmental models to explain variation in timing and rate of scaup migration at large-scale and local levels. Spring migration of scaup occurred earlier and faster during springs with warmer temperatures and greater precipitation, variables known to influence energy budgets and wetland availability. Our results suggest that surveys designed to index abundance of breeding mallards is imprecise for estimating scaup abundance, and inaccurate at estimating breeding population size by survey stratum.

Journal of Wildlife Management↗
USGS2002

Effectiveness of rodent control and monitoring techniques for a montane rainforest

Introduced black ( Rattus rattus ) and Polynesian ( R. exulans ) rats are damaging to native birds, insects, and plants in island ecosystems. We controlled rodent populations in a montane rainforest on the island of Hawaii to determine feasibility, cost, and effectiveness of ground-based rodent control in a rugged, remote rainforest habitat. Treatment was conducted 1996-99, from January to April each year, using rodenticide bait stations and snap-traps. We monitored rodent numbers in 48-ha treatment and reference areas before, during, and after control. As indexed by presence of rat sign in tracking tunnels or census blocks, rodent control reduced rodent abundance 58-90% each year 1 month after treatment began. There was an influx of rats into the treatment area, as shown by higher than expected numbers of rats snap-trapped on the treatment perimeter. Rodent numbers recovered to approximate pretreatment levels by the beginning of the following treatment year. Coast of equipment and supplies for rodent control for the first year was about \$7,000 for a 1-km 2 grid. After the first year, cost decreased to about \$2,000 for 1 km 2 per year. Rodent control applied continuously for 4 months each year during the breeding season may be effective in protecting nesting forest birds, but will not provide protection to plants and invertebrates vulnerable to predation throughout the year, and it is not likely to protect avian food resources.

Hawaii↗
USGS2005

Variability in colony attendance of crevice-nesting horned puffins: Implications for population monitoring

It is difficult to survey crevice-nesting seabirds because nest-sites are hard to identify and count, and the number of adult birds attending a colony can be extremely variable within and between days. There is no standardized method for surveying crevice-nesting horned puffins ( Fratercula corniculata ), and consequently little is known about abundance or changes in their numbers. We examined the variability in colony attendance of horned puffins at 5 breeding colonies in the North Pacific to assess whether variation in count data can be reduced to a level that would allow us to detect changes in the number of birds attending a colony. We used within-year measures of variation in attendance to examine the power to detect a change in numbers between 2 years, and we used measures of among-year variation to examine the power to detect trends over multiple years. Diurnal patterns of attendance differed among colonies, and among-day variation in attendance was generally lowest from mid- to late-incubation to early chick rearing. Within-year variation in water counts was lower than in land counts, and variation was lower using a daily index based on 5 counts per day than it was using 1 count per day. Measures of among-year variation in attendance also were higher for land-based than water-based counts, and they were higher when we used a 10-day survey period than when we used a 30-day period. The use of either 1 or 5 counts a day during the colony-specific diurnal peak of attendance had little influence on levels of among-year variation. Overall, our study suggests that variation in count data may be reduced to a level that allows detection of trends in numbers. However, more studies of interannual variability in horned puffin attendance are needed. Further, the relationship between count data and breeding population size needs more study before the number of birds present at the colony can be used with confidence as an index of population trend.

Buldir Island, Chowiet Island, Duck Island, Suklik↗
USGS2005

Avian cholera in waterfowl: the role of lesser snow and Ross's geese as carriers of avian cholera in the Playa Lakes region

We collected samples from apparently healthy geese in the Playa Lakes Region (USA) during the winters of 2000a??01 and 2001a??02 to determine whether carriers of Pasteurella multocida, the bacterium that causes avian cholera, were present in wild populations. With the use of methods developed in laboratory challenge trials (Samuel et al., 2003a) and a serotype-specific polymerase chain reaction method for identification of P. multocida serotype 1, we found that a small proportion of 322 wild birds (<5%) were carriers of pathogenic P. multocida. On the basis of serology, an additional group of these birds (<10%) were survivors of recent avian cholera infection. Our results confirm the hypothesis that wild waterfowl are carriers of avian cholera and add support for the hypothesis that wild birds are a reservoir for this disease. In concert with other research, this work indicates that enzootic infection with avian cholera occurs in lesser snow goose (Chen caerulescens caerulescens) populations throughout their annual cycle. Although fewer Rossa??s geese (Chen rossii) were sampled, we also found these birds were carriers of P. multocida. Even in the absence of disease outbreaks, serologic evidence indicates that chronic disease transmission and recent infection are apparently occurring year-round in these highly gregarious birds and that a small portion of these populations are potential carriers with active infection.

Colorado, Kansas, New Mexico, Oklahoma, Texas↗
USGS2013

Modelling interactions of toxicants and density dependence in wildlife populations

1. A major challenge in the conservation of threatened and endangered species is to predict population decline and design appropriate recovery measures. However, anthropogenic impacts on wildlife populations are notoriously difficult to predict due to potentially nonlinear responses and interactions with natural ecological processes like density dependence. 2. Here, we incorporated both density dependence and anthropogenic stressors in a stage-based matrix population model and parameterized it for a density-dependent population of peregrine falcons Falco peregrinus exposed to two anthropogenic toxicants [dichlorodiphenyldichloroethylene (DDE) and polybrominated diphenyl ethers (PBDEs)]. Log-logistic exposure–response relationships were used to translate toxicant concentrations in peregrine falcon eggs to effects on fecundity. Density dependence was modelled as the probability of a nonbreeding bird acquiring a breeding territory as a function of the current number of breeders. 3. The equilibrium size of the population, as represented by the number of breeders, responded nonlinearly to increasing toxicant concentrations, showing a gradual decrease followed by a relatively steep decline. Initially, toxicant-induced reductions in population size were mitigated by an alleviation of the density limitation, that is, an increasing probability of territory acquisition. Once population density was no longer limiting, the toxicant impacts were no longer buffered by an increasing proportion of nonbreeders shifting to the breeding stage, resulting in a strong decrease in the equilibrium number of breeders. 4. Median critical exposure concentrations, that is, median toxicant concentrations in eggs corresponding with an equilibrium population size of zero, were 33 and 46 μg g −1 fresh weight for DDE and PBDEs, respectively. 5. Synthesis and applications. Our modelling results showed that particular life stages of a density-limited population may be relatively insensitive to toxicant impacts until a critical threshold is crossed. In our study population, toxicant-induced changes were observed in the equilibrium number of nonbreeding rather than breeding birds, suggesting that monitoring efforts including both life stages are needed to timely detect population declines. Further, by combining quantitative exposure–response relationships with a wildlife demographic model, we provided a method to quantify critical toxicant thresholds for wildlife population persistence.

California↗