50 research outputs found

    Wayward Youth: Trans-Beringian Movement and Differential Southward Migration by Juvenile Sharp-tailed Sandpipers

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    The sharp-tailed sandpiper (Calidris acuminata) is a long-distance migrant that travels each year from breeding grounds in the Russian Arctic to nonbreeding areas in Australasia. Most adults migrate rapidly from breeding grounds along a largely inland route through Asia. Here we report on the highly unusual migratory strategy of this species in which some juveniles, but virtually no adults, take a pronounced detour to western Alaska before proceeding on southward migration. We analyzed data from our own studies in this region and published and unpublished observations and specimen records of sharptailed sandpipers from the entire Pacific Basin. Each autumn, sharp-tailed sandpipers began arriving on coastal graminoid meadows and intertidal habitats throughout western Alaska during the last half of August and the last sandpipers departed from southwestern Alaska during October and November. Body mass of birds banded or collected across multiple years and sites in western Alaska (n = 330) increased by an average of 0.57 ± 0.06 g per day between mid-August and late October. Records suggest a small, regular movement of juveniles (and a very few adults) along the Asiatic coast, but we estimate from surveys that a few tens of thousands of juveniles stage in western Alaska each autumn. The distribution of sight and specimen records from the Pacific Basin during autumn suggests strongly age-segregated migration routes, with the principal migration of juveniles crossing central and western Oceania in a possible nonstop trans-Pacific flight from Alaska. This is only the second well-documented case of differential migration among birds that involves different routes for adults and juveniles, and it raises intriguing questions about how and why this system has evolved.  Le bécasseau à queue pointue (Calidris acuminata) est un migrant de longue distance qui se déplace chaque année depuis les zones de reproduction de l’Arctique russe jusqu’aux zones de non-reproduction de l’Australasie. La plupart des adultes migrent rapidement à partir des zones de reproduction le long d’un corridor largement situé à l’intérieur qui traverse l’Asie. Ici, nous faisons état de la stratégie migratoire grandement inhabituelle de cette espèce dans le cadre de laquelle certains juvéniles, mais quasiment aucun adulte, font une déviation prononcée vers l’ouest de l’Alaska avant de migrer vers le Sud. Nous avons analysé les données dérivées de nos propres études dans la région de même que des observations publiées et inédites et des enregistrements de spécimens de bécasseaux à queue pointue de tout le bassin du Pacifique. Chaque automne, les bécasseaux à queue pointue commençaient à arriver sur les prés côtiers de graminoïdes et dans les habitats intertidaux de l’ouest de l’Alaska pendant la deuxième moitié du mois d’août. Les derniers bécasseaux quittaient le sud-ouest de l’Alaska aux mois d’octobre et de novembre. La masse corporelle des oiseaux en bandes ou recueillis au cours de plusieurs années et à plusieurs emplacements de l’ouest de l’Alaska (n = 330) a augmenté en moyenne de 0,57 ± 0,06 g par jour entre la mi-août et la fin octobre. Les données laissent voir la présence d’un petit mouvement régulier de juvéniles (et très peu d’adultes) le long de la côte asiatique, mais nous avons estimé d’après les dénombrements que quelques dizaines de milliers de juvéniles passent un certain temps dans l’ouest de l’Alaska chaque automne. La répartition d’enregistrements d’observations et de spécimens du bassin du Pacifique à l’automne laisse entrevoir des routes migratoires fortement ségrégées en fonction de l’âge et que la migration principale de juvéniles traversant le centre et l’ouest de l’Océanie dans le cadre d’un vol transpacifique est susceptible d’être sans escale depuis l’Alaska. Il s’agit seulement du deuxième cas bien répertorié de migration différentielle d’oiseaux dont les trajets diffèrent chez les adultes et les juvéniles, et cela soulève des questions à savoir comment et pourquoi ce système a évolué

    Residency Times and Patterns of Movement of Postbreeding Dunlin on a Subarctic Staging Area in Alaska

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    Understanding how individuals use key resources is critical for effective conservation of a population. The Yukon-Kuskokwim Delta (YKD) in western Alaska is the most important postbreeding staging area for shorebirds in the subarctic North Pacific, yet little is known about movements of shorebirds there during the postbreeding period. To address this information gap, we studied residency times and patterns of movement of 17 adult and 17 juvenile radio-marked Dunlin (Calidris alpina) on the YKD between early August and early October 2005. Throughout this postbreeding period, during which Dunlin were molting, most birds were relocated within a 130 km radius of their capture site on the YKD, but three birds were relocated more than 600 km to the south at estuaries along the Alaska Peninsula. On average, juvenile Dunlin were relocated farther away from the banding site (median relocation distance = 36.3 km) than adult Dunlin (median relocation distance = 8.8 km). Post-capture, minimum lengths of stay by Dunlin on the YKD were not significantly different between juveniles (median = 19 days) and adults (median = 23 days), with some birds staging for more than 50 days. Body mass at time of capture was the best single variable explaining length of stay on the YKD, with average length of stay decreasing by 2.5 days per additional gram of body mass at time of capture. Conservation efforts for postbreeding shorebirds should consider patterns of resource use that may differ not only by age cohort but also by individual condition.Pour donner lieu à la conservation efficace d’une population, il est essentiel de comprendre comment les individus se servent des ressources importantes. Le delta Yukon-Kuskokwim, dans l’ouest de l’Alaska, est l’escale de post-reproduction la plus importante des oiseaux de rivage du Pacifique Nord subarctique. Pourtant, on en sait peu sur les déplacements des oiseaux de rivage à cet endroit pendant la période de post-reproduction. Afin de combler ce manque d’information, nous avons étudié les durées de résidence et les habitudes de déplacement de 17 bécasseaux variables (Calidris alpina) adultes et de 17 bécasseaux variables juvéniles radio-marqués dans le delta Yukon-Kuskokwim du début août au début octobre 2005. Pendant la période de post-reproduction pendant laquelle les bécasseaux variables muaient, la plupart des oiseaux ont été déplacés dans un rayon de 130 km de leur lieu de capture dans le delta Yukon-Kuskokwim, mais trois oiseaux ont été relocalisés à plus de 600 km vers le sud, aux estuaires le long de la péninsule de l’Alaska. En moyenne, les bécasseaux variables juvéniles ont été déplacés plus loin du lieu de baguage (distance de déplacement médiane = 36,3 km) que les bécasseaux variables adultes (distance de déplacement médiane = 8,8 km). Par bécasseau variable, les durées de séjour minimales après la capture au delta Yukon-Kuskokwim ne différaient pas considérablement entre les juvéniles (médiane = 19 jours) et les adultes (médiane = 23 jours), certains oiseaux faisant escale pendant plus de 50 jours. La masse corporelle au moment de la capture était la meilleure et la seule variable expliquant la durée du séjour au delta Yukon-Kuskokwim, la durée moyenne du séjour diminuant de 2,5 jours par gramme supplémentaire de masse corporelle au moment de la capture. Les efforts de conservation des oiseaux de rivage en période de post-reproduction devraient tenir compte des modèles d’utilisation des ressources qui risquent de différer non seulement en fonction de la cohorte d’âge, mais également en fonction de l’état de l’individu

    A Natural Experiment on the Condition-Dependence of Achromatic Plumage Reflectance in Black-Capped Chickadees

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    Honest advertisement models posit that only individuals in good health can produce and/or maintain ornamental traits. Even though disease has profound effects on condition, few studies have experimentally tested its effects on trait expression and even fewer have identified a mechanistic basis for these effects. Recent evidence suggests that black and white, but not grey, plumage colors of black-capped chickadees (Poecile atricapillus) are sexually selected. We therefore hypothesized that birds afflicted with avian keratin disorder, a condition that affects the beak and other keratinized tissues, would show reduced expression of black and white, but not grey, color. UV-vis spectrometry of black-capped chickadees affected and unaffected by avian keratin disorder revealed spectral differences between them consistent with this hypothesis. To elucidate the mechanistic bases of these differences, we used scanning electron microscopy (SEM), electron-dispersive x-ray spectroscopy (EDX) and a feather cleaning experiment. SEM showed extreme feather soiling in affected birds, and EDX revealed that this was most likely from external sources. Experimentally cleaning the feathers increased color expression of ornamental feathers of affected, but not unaffected, birds. These data provide strong evidence that black and white color is an honest indicator in chickadees, and that variation in feather dirtiness, likely due to differences in preening behavior is a mechanism for this association

    The Pacific as the world’s greatest theater of bird migration:Extreme flights spark questions about physiological capabilities, behavior, and the evolution of migratory pathways

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    The Pacific Basin, by virtue of its vastness and its complex aeroscape, provides unique opportunities to address questions about the behavioral and physiological capabilities and mechanisms through which birds can complete spectacular flights. No longer is the Pacific seen just as a formidable barrier between terrestrial habitats in the north and the south, but rather as a gateway for specialized species, such as shorebirds, to make a living on hemispherically distributed seasonal resources. This recent change in perspective is dramatic, and the research that underpins it has presented new opportunities to learn about phenomena that often challenge a sense of normal. Ancient Polynesians were aware of the seasonal passage of shorebirds and other landbirds over the Pacific Ocean, incorporating these observations into their navigational “tool kit” as they explored and colonized the Pacific. Some ten centuries later, systematic visual observations and tracking technology have revealed much about movement of these shorebirds, especially the enormity of their individual nonstop flights. This invites a broad suite of questions, often requiring comparative studies with bird migration across other ocean basins, or across continents. For example, how do birds manage many days of nonstop exercise apparently without sleep? What mechanisms explain birds acting as if they possess a Global Positioning System? How do such extreme migrations evolve? Through advances in both theory and tracking technology, biologists are poised to greatly expand the horizons of movement ecology as we know it. In this integrative review, we present a series of intriguing questions about trans-Pacific migrant shorebirds and summarize recent advances in knowledge about migratory behavior operating at temporal scales ranging from immediate decisions during a single flight, to adaptive learning throughout a lifetime, to evolutionary development of migratory pathways. Recent advances in this realm should stimulate future research across the globe and across a broad array of disciplines

    Feasibility of achieving the 2025 WHO global tuberculosis targets in South Africa, China, and India: a combined analysis of 11 mathematical models.

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    BACKGROUND: The post-2015 End TB Strategy proposes targets of 50% reduction in tuberculosis incidence and 75% reduction in mortality from tuberculosis by 2025. We aimed to assess whether these targets are feasible in three high-burden countries with contrasting epidemiology and previous programmatic achievements. METHODS: 11 independently developed mathematical models of tuberculosis transmission projected the epidemiological impact of currently available tuberculosis interventions for prevention, diagnosis, and treatment in China, India, and South Africa. Models were calibrated with data on tuberculosis incidence and mortality in 2012. Representatives from national tuberculosis programmes and the advocacy community provided distinct country-specific intervention scenarios, which included screening for symptoms, active case finding, and preventive therapy. FINDINGS: Aggressive scale-up of any single intervention scenario could not achieve the post-2015 End TB Strategy targets in any country. However, the models projected that, in the South Africa national tuberculosis programme scenario, a combination of continuous isoniazid preventive therapy for individuals on antiretroviral therapy, expanded facility-based screening for symptoms of tuberculosis at health centres, and improved tuberculosis care could achieve a 55% reduction in incidence (range 31-62%) and a 72% reduction in mortality (range 64-82%) compared with 2015 levels. For India, and particularly for China, full scale-up of all interventions in tuberculosis-programme performance fell short of the 2025 targets, despite preventing a cumulative 3·4 million cases. The advocacy scenarios illustrated the high impact of detecting and treating latent tuberculosis. INTERPRETATION: Major reductions in tuberculosis burden seem possible with current interventions. However, additional interventions, adapted to country-specific tuberculosis epidemiology and health systems, are needed to reach the post-2015 End TB Strategy targets at country level. FUNDING: Bill and Melinda Gates Foundation

    Cost-effectiveness and resource implications of aggressive action on tuberculosis in China, India, and South Africa: a combined analysis of nine models.

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    BACKGROUND: The post-2015 End TB Strategy sets global targets of reducing tuberculosis incidence by 50% and mortality by 75% by 2025. We aimed to assess resource requirements and cost-effectiveness of strategies to achieve these targets in China, India, and South Africa. METHODS: We examined intervention scenarios developed in consultation with country stakeholders, which scaled up existing interventions to high but feasible coverage by 2025. Nine independent modelling groups collaborated to estimate policy outcomes, and we estimated the cost of each scenario by synthesising service use estimates, empirical cost data, and expert opinion on implementation strategies. We estimated health effects (ie, disability-adjusted life-years averted) and resource implications for 2016-35, including patient-incurred costs. To assess resource requirements and cost-effectiveness, we compared scenarios with a base case representing continued current practice. FINDINGS: Incremental tuberculosis service costs differed by scenario and country, and in some cases they more than doubled existing funding needs. In general, expansion of tuberculosis services substantially reduced patient-incurred costs and, in India and China, produced net cost savings for most interventions under a societal perspective. In all three countries, expansion of access to care produced substantial health gains. Compared with current practice and conventional cost-effectiveness thresholds, most intervention approaches seemed highly cost-effective. INTERPRETATION: Expansion of tuberculosis services seems cost-effective for high-burden countries and could generate substantial health and economic benefits for patients, although substantial new funding would be required. Further work to determine the optimal intervention mix for each country is necessary. FUNDING: Bill & Melinda Gates Foundation
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