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The condor
Cooper Ornithological Society
The condor

Cooper Ornithological Society

0010-5422

The condor/Journal The condor
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    A parasite reduction conservation intervention does not improve fledging success or most condition metrics for Purple Martins

    Williams, Heather M.Dittmar, KatharinaPagano, Susan Smith
    14页
    查看更多>>摘要：Eastern Purple Martins (Prognesubis subis) have an unusually close relationship with humans, as they nest exclusively in man-made nest boxes. Current conservation policy directly promotes further interaction with this species by advocating regular replacement of nest materials during the nestling phase to reduce ectoparasite load and increase nestling fitness. We conducted the first test of the efficacy of this recommendation and found that it was partially effective in reducing parasite abundance, but had no effect on nestling fledging success, body mass, leukocyte count, or triglyceride or uric acid concentration. We found a small but significant increase in nestling hematocrit associated with nest material replacement, implying that parasites may induce nestling anemia. Contrary to our expectations, we also found elevated heterophil/lymphocyte ratios in nestlings with replacements, possibly indicating elevated physiological stress associated with nest replacements. Based on our results, we do not recommend nest material replacements to combat routine parasite infestations.
      原文链接:
    • NSTL
    • Oxford Univ Press

    Mixed evidence for effects of stewardship on Least Tern reproductive success in coastal Mississippi

    Darrah, Abigail J.
    13页
    查看更多>>摘要：Disturbance from human activity can cause reduced productivity of coastal birds that nest on sandy beaches. A common method to protect coastal birds from human disturbance is the use of signs and fencing to close off a section of beach used for breeding. This management action requires public compliance and might require enforcement, such as in the use of volunteer stewards stationed at protected colonies that provide education and enforcement. I assessed the effectiveness of active stewardship as a conservation measure to protect nesting Least Terns (Sternula antillarum) in coastal Mississippi by determining if colony-level productivity (fledglings produced per nest) was correlated with stewardship effort (hours that stewards protected each colony), the rate of disturbance from human and natural sources, and additional factors. Observers surveyed 24 Least Tern colonies in Harrison County, Mississippi, twice weekly during the 2017-2019 breeding seasons to record the number of nests present, the fate of marked nests, predator tracks within the colony, and the number of fledglings produced per colony. Concurrently, during their work shifts, stewards recorded all sources and durations of disturbance events that caused the terns to flush or respond with defense. Least Tern daily nest survival increased with colony size and stewardship effort, and was lower during intervals that included weekends and evidence of owl presence.Total productivity was negatively associated with avian predator disturbance rate and the total time adults spent flushed, but was not associated with stewardship effort. The results of this study demonstrate that active stewardship can have a positive effect on LeastTern productivity by increasing nest success, whereas current stewardship practices were not sufficient to increase chick survival, even in a system with a paucity of ground predators.
      原文链接:
    • NSTL
    • Oxford Univ Press

    Integrating vulture social behavior into conservation practice

    Blanco, GuillermoMoleon, MarcosMargalida, AntoniAntonio Sanchez-Zapata, Jose...
    20页
    查看更多>>摘要：Vultures are one of the most threatened bird groups globally. Although many of the threats faced by vultures have been identified, the impact of human activities on the social life of vultures has received little attention. In this paper, we emphasize the need to integrate vulture sociality into conservation practice. First, we summarize current knowledge on vulture social behavior, and the evolutionary and ecological roots of their breeding systems. We describe the existence of contrasting gradients in social foraging strategies and hierarchical social structures among colonial and territorial breeders associated with species (and population) reliance on carrion differing in size and predictability. We also highlight the potential role of vulture gatherings in maintaining population-level social structures and for mate-finding given high mate-selectivity. Next, based on this social framework, we discuss the impact of human activities on social foraging, territory structures, resource partitioning processes, and mating dynamics. However, little is known about how disruptions of social habits may have contributed to vulture population declines and/or may impede their recovery. Lastly, we provide directions for future research on vulture socio-ecology that may improve current conservation efforts. We encourage researchers and wildlife managers to pay more attention to natural carrion diversity underlying vulture social system diversity, especially when implementing supplementary feeding programs, and to consider the complex mating and settlement dynamics in reintroduction programs. Overall, we stress that understanding the complex social life of vultures is critical to harmonize their conservation with anthropogenic activities.
      原文链接:
    • NSTL
    • Oxford Univ Press

    Dunlin subspecies exhibit regional segregation and high site fidelity along the East Asian-Australasian Flyway

    Lagasse, Benjamin J.Lanctot, Richard B.Barter, MarkBrown, Stephen...
    15页
    查看更多>>摘要：The degree to which individuals migrate among particular breeding, migration, and wintering sites can have important implications for prioritizing conservation efforts. Four subspecies of Dunlin (Calidris alpina) migrate along the East Asian-Australasian Flyway. Each subspecies has a distinct and well-defined breeding range, but their migration and winter ranges are poorly defined or unknown. We assessed the migratory connectivity of 3 of these subspecies by evaluating a dataset that encompasses 57 yr (1960-2017), and comprises more than 28,000 Dunlin banding records and 818 observations (71 recaptures and 747 band resightings). We present some of the first evidence that subspecific segregation likely occurs, with arcticola Dunlin wintering in areas of Japan, and other arcticola, actites, and sakhalina Dunlin wintering in areas of the Yellow and China seas. Observations indicate that whether an arcticola Dunlin winters in Japan or the Yellow and China seas is independent of their breeding location, sex, or age. Furthermore, observations indicate that 83% of arcticola Dunlin exhibit interannual site fidelity to specific wintering sites. This suggests that the degradation of specific wetland areas may negatively affect particular individuals of a particular subspecies (or combination of subspecies), and, if widespread, could result in population declines. Given the possible biases inherent in analyzing band recovery data, we recommend additional flyway-wide collaboration and the use of lightweight tracking devices and morphological and genetic assignment techniques to better quantify subspecies' migratory movements and nonbreeding distributions. This information, when combined, will enable effective conservation efforts for this species across the East Asian-Australasian Flyway.
      原文链接:
    • NSTL
    • Oxford Univ Press

    Riparian habitat restoration increases the availability and occupancy of Yellow-breasted Chat territories but brood parasitism is the primary influence on reproductive performance

    Forrester, Timothy R.Green, David J.Bezener, A. MichaelBishop, Christine A....
    16页
    查看更多>>摘要：Implementation and evaluation of conservation efforts requires an understanding of the habitat selection and reproductive success of endangered populations. As populations recover, established territory holders may force new arrivals into lower quality habitat, which can reduce reproductive success, especially in disturbed landscapes where suitable habitat is scarce. The endangered Western Yellow-breasted Chat (Icteria virens auricollis) population in the fragmented riparian zone of the Okanagan Valley, British Columbia, Canada, has rapidly increased in response to habitat restoration. During this population increase from 2002 to 2014, we monitored 485 chat nests in 157 breeding territories to evaluate the influences of habitat selection, habitat restoration, and brood parasitism by Brown-headed Cowbirds (Molothrus ater) on reproductive performance. We found that, in protected reference sites, breeding territories that were occupied in the early years of the study had higher percent shrub cover than territories that were first occupied in the later years of the study, indicating that chats preferred territories with high shrub cover. Conversely, in restoration sites, later-occupied territories had similarly high shrub cover as earlier-occupied territories, suggesting that restoration activities enabled chats to continually settle in territories with high shrub cover. Yet, we did not find strong evidence that nest site vegetation characteristics or habitat restoration influenced reproductive performance. Instead, the high rate of brood parasitism (49%), which reduced nest success and productivity, was the dominant influence on reproductive performance. However, this recovering population still had high daily nest survival (0.974) and productivity (2.72 fledglings per successful nest) compared with other riparian songbirds and the high parasitism rate did not prevent the population from increasing. Thus, conservation efforts for Yellow-breasted Chats should focus on restoring riparian shrubs, even within heavily developed landscapes, to increase the number of potential breeding territories, while also quantifying how brood parasitism influences reproductive performance.
      原文链接:
    • NSTL
    • Oxford Univ Press

    Plunging floater survival causes cryptic population decline in the Common Loon

    Piper, Walter H.Grear, JasonHoover, BrianLomery, Elaina...
    10页
    查看更多>>摘要：Populations of many vertebrates are declining and geographic ranges contracting, largely as a consequence of anthropogenic threats. Many reports of such decline, however, lack the breadth and detail to narrow down its causes. Here we describe population decline in the Common Loon (Gavia immer), a charismatic aquatic bird, based on systematic resighting and measurement of a marked population. During our 27-year investigation, age-adjusted chick mass has fallen by 11%, mortality among young and old chicks has increased by 31% and 82%, respectively, and fledging success has declined by 26%. Meanwhile, the return rate of marked nonbreeders ("floaters") has plunged by 53%, and the adult population overall has declined by 22%. Consistent with the thinning ranks of floaters, the rate of territory eviction has decreased by 52% during the study. Despite the decline in floaters, territory occupancy remains unchanged. However, a matrix model, updated with recent estimates for breeding success, juvenile survival, and senescence, yields a recalculated deterministic population growth rate (X) of 0.94 for our study population, which suggests that declines in vital rates could lead to a loss of 52% of the current population and a decline of 37% in territory occupancy by 2031. Lack of data on floaters in other upper Midwest and New England loon populations leaves their status in doubt.
      原文链接:
    • NSTL
    • Oxford Univ Press

    Post-fledging Golden-winged Warblers require forests with multiple stand developmental stages

    Fiss, Cameron J.McNeil, Darin J.Rodewald, Amanda D.Duchamp, Joseph E....
    13页
    查看更多>>摘要：Our understanding of songbird habitat needs during the breeding season stems largely from studies of nest success. However, growing evidence shows that nesting habitat and post-fledging habitat often differ. Management guidelines for declining species need to be reevaluated and updated to account for habitat shifts that may occur across the full breeding cycle. The Golden-winged Warbler (Vermivora chrysoptera) is a declining songbird species for which best management practices (BMPs) are based overwhelmingly on nesting habitat. We studied stand-scale habitat selection by fledgling Golden-winged Warblers during May-July, 2014-2017, in 2 landscapes (2 yr of data for each landscape), 200 km apart in Pennsylvania. Across 4 yr, we radio-tagged and tracked 156 fledglings. We used discrete-choice models to evaluate habitat selection during 2 post-fledging time periods (days 1-5, days 6-28). Fledglings used a variety of cover types, but most telemetry relocations (i.e. 85%) occurred in forest in the stand initiation stage, stem exclusion stage, or mature forest upland. Fledglings primarily selected stand initiation forest during the first 5 days, but preferred habitats differed between regions during days 6-28 post-fledging. Fledglings in one landscape favored stands in the stem exclusion stage while fledglings in the other landscape continued to select stands in the initiation stage. Fledglings moved greater distances as they aged and dispersed similar to 750 m by day 28 post-fledging.These findings suggest the need to update Golden-winged Warbler BMPs to account for the broader habitat needs of fledglings during the breeding season. In addition, these results indicate that regional studies of habitat requirements can help guide management of dynamic forest landscapes for birds.
      原文链接:
    • NSTL
    • Oxford Univ Press

    Seasonal rainfall in subtropical montane cloud forests drives demographic fluctuations in a Green-backed Tit population

    Shiao, Ming-TangChuang, Mei-ChenYuan, Hsiao-WeiWang, Ying...
    15页
    查看更多>>摘要：Montane birds are vulnerable to climate change. However, the mechanisms by which weather drives demographic processes in montane birds have seldom been investigated. We conducted a long-term study (2009-2019) on the Green-backed Tit (Parus monticolus), an insectivorous passerine, in the montane cloud forest of subtropical Taiwan. We explored the effects of weather variability on the productivity and survival of adult Green-backed Tits. Nest survival was negatively associated with seasonal rainfall during the breeding season (April-July) and was lower in early clutches than in late clutches. Higher typhoon-induced precipitation during the postbreeding period (July-September) was related to reduced adult survival, but neither summer temperature nor winter weather conditions were found to be related to adult bird survival. We developed a stochastic simulation model for Green-backed Tit population dynamics based on empirical data. We compared the simulated time-series and observed population growth rates (lambda) and found that 80% (8/10 yr) of the observed lambda fell within the 5th and 95th percentiles of the simulated data over the 10-yr period. Moreover, the simulated average (+/- standard deviation) of the geometric mean of lambda over 10 yr (1.05 +/- 0.07) was close to that observed from 2009 to 2019 (0.99), which provided confidence that the model effectively simulated the population growth rate of the Green-backed Tit. We conducted a sensitivity analysis for lambda and found that juvenile and adult survival influenced by typhoon-induced rainfall were the greatest contributors to the variance in the growth rate of the Green-backed Tit population. With the onset of intensified seasonal precipitation associated with global warming, the population growth and density of Green-backed Tits will decline substantially. Our results suggest that under scenarios of high emissions of greenhouse gas, this local population of Green-backed Tits will not persist in the near future.
      原文链接:
    • NSTL
    • Oxford Univ Press

    Tree Swallow selection for wetlands in agricultural landscapes predicted by central-place foraging theory

    Elgin, Andrew S.Clark, Robert G.Morrissey, Christy A.
    12页
    查看更多>>摘要：Millions of wetland basins, embedded in croplands and grasslands, are biodiversity hotspots in North America's Prairie Pothole Region, but prairie wetlands continue to be degraded and drained, primarily for agricultural activities. Aerial insectivorous swallows are known to forage over water, but it is unclear whether swallows exhibit greater selection for wetlands relative to other habitats in croplands and grasslands. Central-place foraging theory suggests that habitat selectivity should increase with traveling distance from a central place, such that foragers compensate for traveling costs by selecting more profitable foraging habitat. Using global positioning system (GPS) tags, we evaluated habitat selection by female Tree Swallows (Tachycineta bicolor) at 4 sites containing wetlands and where terrestrial land cover was dominated by grasslands (grass, herbaceous cover) and/or cultivated cropland. We also used sweep-net transects to assess the abundance and biomass of flying insects in different habitats available to swallows (wetland pond margins, grassy field margins, and representative uplands). As expected for a central-place forager, GPS-tagged swallows selected more for wetland ponds (disproportionate to availability), and appeared to increasingly select for wetlands with increasing distance from their nests. On cropland-dominated sites, insect abundance and biomass tended to be higher in pond margins or grassy field margins compared to cropped uplands, while abundance and biomass were more uniform among sampled habitats at sites dominated by grass and herbaceous cover. Swallow habitat selection was not clearly explained by the distribution of sampled insects among habitats; however, traditional terrestrial sampling methods may not adequately reflect prey distribution and availability to aerially foraging swallows. Overall, our results underscore the importance of protecting and enhancing prairie wetlands and other non-crop habitats in agricultural landscapes, given their disproportionate use and capacity to support breeding swallow and insect populations.
      原文链接:
    • NSTL
    • Oxford Univ Press

    Vegetation management on private forestland can increase avian species richness and abundance

    Wood, Jesse M.Tegeler, Amy K.Ross, Beth E.
    16页
    查看更多>>摘要：Conservation efforts on private lands are important for biodiversity conservation. On private lands in South Carolina, in the southeastern United States, forestry management practices (prescribed burning, thinning, herbicide application) are used to improve upland pine habitat for wildlife and timber harvest and are incentivized through U.S. Department of Agriculture Farm Bill cost-share programs. Because many forest-dependent avian species have habitat requirements created primarily through forest management, data are needed on the effectiveness of these management activities. We studied privately owned loblolly pine (Pinus taeda) stands in the South Carolina Piedmont region. Our objective was to understand how management practices influence avian species richness and abundance at local (forest stand) and landscape levels in relatively small stands (average similar to 28 ha). We surveyed 49 forest stands during 2 bird breeding seasons with traditional point counts and vegetation surveys. We evaluated the effects of management on pine stand characteristics, avian species richness, and abundance of state-designated bird species of concern. Repeated burning and thinning shifted stand conditions to open pine woodlands with reduced basal area and herbaceous understories. Stands with lower basal area supported greater avian species richness. Some species increased in abundance in response to active management (e.g., Brown-headed Nuthatch [Sitta pusilla] and Indigo Bunting [Passerina cyanea]), but relationships varied. Some species responded positively to increases in forest quantity at a landscape scale (1-5 km; e.g., Northern Bobwhite [Colinus virginianus]). We found species-rich avian communities and species of conservation concern on working timber lands, indicating that incentivized forest management on private lands can provide valuable habitat for wildlife.
      原文链接:
    • NSTL
    • Oxford Univ Press