139 research outputs found
Habitat Characteristics of Polar Bear Terrestrial Maternal Den Sites in Northern Alaska
Polar bears (Ursus maritimus) give birth to and nurture their young in dens of ice and snow. During 1999-2001, we measured the structure of 22 dens on the coastal plain of northern Alaska after polar bear families had evacuated their dens in the spring. During the summers of 2001 and 2002, we revisited the sites of 42 maternal and autumn exploratory dens and recorded characteristics of the under-snow habitat. The structure of polar bear snow dens was highly variable. Most were simple chambers with a single entrance/egress tunnel. Others had multiple chambers and additional tunnels. Thickness of snow above and below dens was highly variable, but most dens were overlain by less than 1 m of snow. Dens were located on, or associated with, pronounced landscape features (primarily coastal and river banks, but also a lake shore and an abandoned oil field gravel pad) that are readily distinguished from the surrounding terrain in summer and catch snow in early winter. Although easily identified, den landforms in northern Alaska were more subtle than den habitats in many other parts of the Arctic. The structure of polar bear dens in Alaska was strikingly similar to that of dens elsewhere and has remained largely unchanged in northern Alaska for more than 25 years. Knowledge of den structure and site characteristics will allow resource managers to identify habitats with the greatest probability of holding dens. This information may assist resource managers in preventing negative impacts of mineral exploration and extraction on polar bears.Les ourses polaires (Ursus maritimus) donnent naissance et nourrissent leurs petits dans des taniĂšres de glace et de neige. De 1999 Ă 2001, on a mesurĂ© la structure de 22 taniĂšres situĂ©es sur la plaine cĂŽtiĂšre de l'Alaska septentrional aprĂšs que les familles d'ours polaires eurent Ă©vacuĂ© leurs taniĂšres au printemps. Au cours des Ă©tĂ©s de 2001 et de 2002, on s'est Ă nouveau rendus sur les sites de 42 taniĂšres de mise bas et d'exploration automnale et on a mesurĂ© les caractĂ©ristiques de l'habitat situĂ© au-dessous de la neige. La structure des taniĂšres d'ourses polaires variait considĂ©rablement. La plupart Ă©taient de simples cavitĂ©s qui possĂ©daient un tunnel servant Ă la fois d'entrĂ©e et de sortie. D'autres comportaient plusieurs salles et des tunnels supplĂ©mentaires. L'Ă©paisseur de la neige au-dessus et au-dessous des taniĂšres Ă©tait trĂšs variable, mais dans la plupart des cas, la couverture de neige Ă©tait infĂ©rieure Ă 1 m. Les taniĂšres Ă©taient situĂ©es sur des reliefs prononcĂ©s ou y Ă©taient associĂ©es (surtout les rives cĂŽtiĂšres ou les berges de fleuves, mais aussi le bord d'un lac et le remblai de gravier d'un champ pĂ©trolifĂšre abandonnĂ©), qui se dĂ©tachent nettement du paysage alentour en Ă©tĂ© et qui retiennent la neige au dĂ©but de l'hiver. MĂȘme si elles Ă©taient facilement identifiables, les formes de relief propices Ă l'Ă©tablissement de taniĂšres dans l'Alaska septentrional Ă©taient plus discrĂštes que les habitats de taniĂšres situĂ©s dans bien d'autres rĂ©gions de l'Arctique. La structure des taniĂšres d'ourses polaires en Alaska offrait une ressemblance frappante avec celle des taniĂšres creusĂ©es ailleurs et elle est restĂ©e largement inchangĂ©e dans le nord de l'Alaska pendant plus de 25 ans. Les connaissances sur la structure des taniĂšres et les caractĂ©ristiques des sites permettront aux gestionnaires de ressources de distinguer les habitats qui sont le plus susceptibles d'abriter des taniĂšres. Cette information peut aider ces gestionnaires Ă prĂ©venir les retombĂ©es nĂ©gatives sur l'ours polaire de l'exploration et de l'exploitation miniĂšres
Post-Den Emergence Behavior of Polar Bears (Ursus maritimus) in Northern Alaska
We observed polar bear (Ursus maritimus) maternity den sites on Alaskaâs North Slope in March 2002 and 2003 in an effort to describe bearsâ post-den emergence behavior. During 40 sessions spanning 459 h, we observed 8 adults and 14 dependent cubs outside dens for 37.5 h (8.2% of total observation time). There was no significant difference between den emergence dates in 2002 (mean = 15 Mar ± 4.1 d) and 2003 (mean = 21 Mar ± 2.1 d). Following initial den breakout, polar bears remained at their den sites for 1.5 to 14 days (mean = 8.1 ± 5.1 d). The average length of stay in dens between emergent periods was significantly shorter in 2002 (1.79 h) than in 2003 (4.82 h). While outside, adult bears were inactive 49.5% of the time, whereas cubs were inactive 13.4% of the time. We found no significant relationships between den emergence activity and weather. Adult polar bears at den sites subjected to industrial activity exhibited significantly fewer bouts of vigilance than denned bears in undisturbed areas (t = -5.5164, df = 4, p = 0.00). However, the duration of vigilance behaviors at sites near industrial activity was not significantly shorter than at the other sites studied (t = -1.8902, df = 4, p = 0.07). Results for these bears were within the range of findings in other studies of denned polar bears.Nous avons observĂ© des taniĂšres de maternitĂ© dâours polaires (Ursus maritimus) sur le versant nord de lâAlaska aux mois de mars 2002 et 2003 dans le but de dĂ©crire le comportement de sortie des ours aprĂšs leur sĂ©jour dans la taniĂšre. Dans le cadre de 40 sĂ©ances dâobservation ayant durĂ© 459 heures, nous avons observĂ© 8 ours adultes et 14 oursons Ă charge en dehors des taniĂšres pendant 37,5 heures (soit 8,2 % de la durĂ©e dâobservation totale). Il nây avait pas de diffĂ©rence importante entre les dates de sortie des taniĂšres en 2002 (moyenne = 15 mars ± 4,1 j) et 2003 (moyenne = 21 mars ± 2,1 j). AprĂšs la premiĂšre sortie de la taniĂšre, les ours polaires restaient Ă lâemplacement de leur taniĂšre pendant 1,5 Ă 14 jours (moyenne = 8,1 ± 5.1 j). La longueur moyenne du sĂ©jour en taniĂšre entre les pĂ©riodes de sortie Ă©tait beaucoup plus courte en 2002 (1,79 h) quâen 2003 (4,82 h). Une fois sortis, les ours adultes Ă©taient inactifs pendant 49,5 % du temps, tandis que les oursons Ă©taient inactifs pendant 13,4 % du temps. Nous nâavons pas trouvĂ© de lien important entre lâactivitĂ© une fois sorti de la taniĂšre et le temps quâil faisait. Les ours polaires adultes Ă lâemplacement de taniĂšres assujetties Ă des activitĂ©s industrielles affichaient beaucoup moins de sĂ©quences de vigilance que les ours en taniĂšre des rĂ©gions tranquilles (t = -5,5164, dl = 4, p = 0,00). Cependant, la durĂ©e des comportements de vigilance aux emplacements situĂ©s prĂšs dâactivitĂ©s industrielles nâĂ©tait pas beaucoup plus courte quâaux autres emplacements Ă©tudiĂ©s (t = - 1,8902, dl = 4, p = 0,07). Les rĂ©sultats enregistrĂ©s pour ces ours tombaient dans lâĂ©tendue des constatations dĂ©coulant dâautres Ă©tudes dâours polaires en taniĂšre
Development of On-Shore Behavior Among Polar Bears (Ursus Maritimus) in the Southern Beaufort Sea: Inherited or Learned?
Polar bears (Ursus maritimus) are experiencing rapid and substantial changes to their environment due to global climate change. Polar bears of the southern Beaufort Sea (SB) have historically spent most of the year on the sea ice. However, recent reports from Alaska indicate that the proportion of the SB subpopulation observed on-shore during late summer and early fall has increased. Our objective was to investigate whether this on-shore behavior has developed through genetic inheritance, asocial learning, or through social learning. From 2010 to 2013, genetic data were collected from SB polar bears in the fall via hair snags and remote biopsy darting on-shore and in the spring from captures and remote biopsy darting on the sea ice. Bears were categorized as either on-shore or off-shore individuals based on their presence onshore during the fall. Levels of genetic relatedness, first-order relatives, motherâoffspring pairs, and fatherâoffspring pairs were determined and compared within and between the two categories: on-shore versus off-shore. Results suggested transmission of on-shore behavior through either genetic inheritance or social learning as there was a higher than expected number of first-order relatives exhibiting on-shore behavior. Genetic relatedness and parentage data analyses were in concurrence with this finding, but further revealed motherâoffspring social learning as the primary mechanism responsible for the development of on-shore behavior. Recognizing that on-shore behavior among polar bears was predominantly transmitted via social learning from mothers to their offspring has implications for future management and conservation as sea ice continues to decline
Estimation of capture probabilities using generalized estimating equations and mixed effects approaches
Modeling individual heterogeneity in capture probabilities has been one of the most challenging tasks in capture-recapture studies. Heterogeneity in capture probabilities can be modeled as a function of individual covariates, but correlation structure among capture occasions should be taking into account. A proposed generalized estimating equations (GEE) and generalized linear mixed modeling (GLMM) approaches can be used to estimate capture probabilities and population size for capture-recapture closed population models. An example is used for an illustrative application and for comparison with currently used methodology. A simulation study is also conducted to show the performance of the estimation procedures. Our simulation results show that the proposed quasi-likelihood based on GEE approach provides lower SE than partial likelihood based on either generalized linear models (GLM) or GLMM approaches for estimating population size in a closed capture-recapture experiment. Estimator performance is good if a large proportion of individuals are captured. For cases where only a small proportion of individuals are captured, the estimates become unstable, but the GEE approach outperforms the other methods
Measuring maternal mortality : an overview of opportunities and options for developing countries
Background:There is currently an unprecedented expressed need and demand for estimates of maternal mortality in developing countries. This has been stimulated in part by the creation of a Millennium Development Goal that will be judged partly on the basis of reductions in maternal mortality by 2015. Methods: Since the launch of the Safe Motherhood Initiative in 1987, new opportunities for data capture have arisen and new methods have been developed, tested and used. This paper provides a pragmatic overview of these methods and the optimal measurement strategies for different developing country contexts. Results: There are significant recent advances in the measurement of maternal mortality, yet also room for further improvement, particularly in assessing the magnitude and direction of biases and their implications for different data uses. Some of the innovations in measurement provide efficient mechanisms for gathering the requisite primary data at a reasonably low cost. No method, however, has zero costs. Investment is needed in measurement strategies for maternal mortality suited to the needs and resources of a country, and which also strengthen the technical capacity to generate and use credible estimates. Conclusion: Ownership of information is necessary for it to be acted upon: what you count is what you do. Difficulties with measurement must not be allowed to discourage efforts to reduce maternal mortality. Countries must be encouraged and enabled to count maternal deaths and act.WJG is funded partially by the University of Aberdeen. OMRC is partially funded by the London School of Hygiene and Tropical Medicine. CS and SA are partially funded by Johns Hopkins University. CAZ is funded by the Health Metrics Network at the World Health Organization. WJG, OMRC, CS and SA are also partially supported through an international research program, Immpact, funded by the Bill & Melinda Gates Foundation, the Department for International Development, the European Commission and USAID
Climate change threatens polar bear populations : a stochastic demographic analysis
Author Posting. © Ecological Society of America, 2010. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Ecology 91 (2010): 2883â2897, doi:10.1890/09-1641.1.The polar bear (Ursus maritimus) depends on sea ice for feeding, breeding, and movement. Significant reductions in Arctic sea ice are forecast to continue because of climate warming. We evaluated the impacts of climate change on polar bears in the southern Beaufort Sea by means of a demographic analysis, combining deterministic, stochastic, environment-dependent matrix population models with forecasts of future sea ice conditions from IPCC general circulation models (GCMs). The matrix population models classified individuals by age and breeding status; mothers and dependent cubs were treated as units. Parameter estimates were obtained from a captureârecapture study conducted from 2001 to 2006. Candidate statistical models allowed vital rates to vary with time and as functions of a sea ice covariate. Model averaging was used to produce the vital rate estimates, and a parametric bootstrap procedure was used to quantify model selection and parameter estimation uncertainty. Deterministic models projected population growth in years with more extensive ice coverage (2001â2003) and population decline in years with less ice coverage (2004â2005). LTRE (life table response experiment) analysis showed that the reduction in λ in years with low sea ice was due primarily to reduced adult female survival, and secondarily to reduced breeding. A stochastic model with two environmental states, good and poor sea ice conditions, projected a declining stochastic growth rate, log λs, as the frequency of poor ice years increased. The observed frequency of poor ice years since 1979 would imply log λs â â 0.01, which agrees with available (albeit crude) observations of population size. The stochastic model was linked to a set of 10 GCMs compiled by the IPCC; the models were chosen for their ability to reproduce historical observations of sea ice and were forced with âbusiness as usualâ (A1B) greenhouse gas emissions. The resulting stochastic population projections showed drastic declines in the polar bear population by the end of the 21st century. These projections were instrumental in the decision to list the polar bear as a threatened species under the U.S. Endangered Species Act.We acknowledge primary funding for model development
and analysis from the U.S. Geological Survey and additional
funding from the National Science Foundation (DEB-0343820
and DEB-0816514), NOAA, the Ocean Life Institute and the
Arctic Research Initiative at WHOI, and the Institute of Arctic
Biology at the University of AlaskaâFairbanks. Funding for the
captureârecapture effort in 2001â2006 was provided by the U.S.
Geological Survey, the Canadian Wildlife Service, the Department
of Environment and Natural Resources of the Government
of the Northwest Territories, and the Polar Continental
Shelf Project, Ottawa, Canada
Potential climatic transitions with profound impact on Europe
We discuss potential transitions of six climatic subsystems with large-scale impact on Europe, sometimes denoted as tipping elements. These are the ice sheets on Greenland and West Antarctica, the Atlantic thermohaline circulation, Arctic sea ice, Alpine glaciers and northern hemisphere stratospheric ozone. Each system is represented by co-authors actively publishing in the corresponding field. For each subsystem we summarize the mechanism of a potential transition in a warmer climate along with its impact on Europe and assess the likelihood for such a transition based on published scientific literature. As a summary, the âtippingâ potential for each system is provided as a function of global mean temperature increase which required some subjective interpretation of scientific facts by the authors and should be considered as a snapshot of our current understanding. <br/
The effect of melatonin treatment on postural stability, muscle strength, and quality of life and sleep in postmenopausal women: a randomized controlled trial
Strategies to Control a Common Carp Population by Pulsed Commercial Harvest
Commercial fisheries are commonly used to manage nuisance fishes in freshwater systems, but such efforts are often unsuccessful. Strategies for successfully controlling a nuisance population of common carpCyprinus carpio by pulsed commercial harvest were evaluated with a combination of (1) field sampling, (2) population estimation and CPUE indexing, and (3) simulation using an exponential semidiscrete biomass dynamics model (SDBDM). The range of annual fishing mortalities (F) that resulted in successful control (F= 0.244â0.265) was narrow. Common carp biomass dynamics were sensitive to unintentional underharvest due to high rates of surplus production and a biomass doubling time of 2.7 years. Simulations indicated that biomanipulation never achieved successful control unless supplemental fishing mortality was imposed. Harvest of a majority of annual production was required to achieve successful control, as indicated by the ecotrophic coefficient (EC). Readily available biomass data and tools such as SDBDMs and ECs can be used in an adaptive management framework to successfully control common carp and other nuisance fishes by pulsed commercial fishing
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