Avian Conservation and Ecology最新文献

A long-term and severe population decline of Rusty Blackbirds (Euphagus carolinus) has motivated biologists to search for possible causes of the decline. Several hypotheses have been forwarded, one of which is that habitat destruction on the overwintering grounds is responsible. Climate change is another possible explanation. We evaluated the population trend of Rusty Blackbirds in Arkansas by modeling their abundance recorded during Christmas Bird Counts conducted between 1965 and 2020. We used generalized additive modeling to evaluate population trends and explored the influence of weather, effort, habitat, and region on those trends. We found that counts of Rusty Blackbirds have increased by about 40 birds in Arkansas between 1965 and 2020; most of the increase occurred after 1995. We also found that proportion of forest land in each count circle’s county was inversely related to counts of Rusty Blackbirds but that temperature was a more important variable. During warmer years, fewer Rusty Blackbirds were counted. Rusty Blackbird geographic distribution also changed by decade; that change accounted for about 15% of the deviance in counts of Rusty Blackbirds. Finally, we observed a relationship between temperature and distribution; Rusty Blackbirds tended to overwinter in the northern portions of the state during warm years and more southerly portions of the state during cold years. Our analytical approach will be useful to anyone evaluating geographic shifts in populations that might be associated with climate change.

The post Weather and regional effects on winter counts of Rusty Blackbirds (Euphagus carolinus) first appeared on Avian Conservation and Ecology.

The ecology of the post-fledging period for small passerine birds is one of the least known stages of the avian life cycle with high rates of mortality for many species. We examined post-fledging survival and site persistence of Oregon Vesper Sparrows (Poocetes gramineus affinis) based on extensive temporal and spatial implementation of mark-resight methodology in western Oregon, 2017–2021. Our analyses focused on a comparison of descriptive apparent survival estimates (i.e., return rates) uncorrected for detectability and modeled apparent survival estimates corrected for detectability using Program MARK. Modeled survival estimates were only slightly higher than descriptive survival estimates at three weeks (0.754 and 0.689), six weeks (0.659 and 0.617), and nine weeks (0.629 and 0.561). Both estimates were lowest at three weeks post-fledging (0.754 and 0.689), and higher in weeks 3–6 (0.874 and 0.897), and weeks 6–9 (0.954 and 0.893). The best supported model included an effect of fledgling age in weeks on survival probability, and additive effects of site, effort, and week of season on detection probability. There was a live resight during the post-fledging period of at least one bird from 94.9% of the successfully fledged nests. Site persistence greater than 50 days was 0.838. Mean site persistence was 78.1 days and longest site persistence for an individual bird was 115 days. Our results suggest that an extensive mark-resight effort can address detectability concerns and provide an approximation of true post-fledging survival estimates. Our post-fledging survival estimates are the highest reported for a grassland bird, and yet they contrast with the expectations of the methodology and the literature on post-fledging survival of grassland birds, which is mostly derived from radio-tracking methodology. These results along with recent meta-analyses from other researchers raise concerns about unreported and unknown but expected mortality in grassland nestlings and fledglings from additive predation due to radio-tracking attachments and devices.

The post High post-fledging survival and site persistence using mark-resight methodology for Oregon Vesper Sparrows in the Willamette Valley, Oregon first appeared on Avian Conservation and Ecology.

Dusky Grouse (Dendragapus obscurus) are an under-monitored game species in Montana and elsewhere across their distribution. Without population monitoring it is difficult to establish appropriate harvest regulations or understand the impact of environmental disturbances (e.g., timber harvest, climate change) on populations. As a first step toward developing methods for unbiased population monitoring, we must identify appropriate sampling sites, which requires knowledge of Dusky Grouse habitat. Our goal was to explore relationships between Dusky Grouse use and habitat characteristics, and then generate a state-wide map predicting Dusky Grouse habitat in Montana using two methods: resource selection functions and random forest classifiers. The Integrated Monitoring in Bird Conservation Regions program provided a multi-year dataset of Dusky Grouse observations, which we reduced to detected (n=132) and pseudo-absent (n=5960) locations, using geospatial datasets to obtain topographic and vegetation characteristics for each location. We evaluated the predictability of the two models using receiver operating characteristics and area under the curve (ROC/AUC) with k-fold cross validation and classification accuracy of an independent dataset of incidental Dusky Grouse locations. We found both models to be highly predictive and multiple habitat characteristics were found to help predict relative probability of use such as proportion of trees with a height of 16–20m and conifer forest vegetation types. We converted both models to binary values and used an ensemble (frequency histogram) approach to combine the models into a final predictive map. Consensus between the resource selection function and random forest models was high (93%) and the ensemble map had higher predictive accuracy when classifying the independent dataset than the other two models. Our results show that our ensembled model approach was able to accurately predict potential Dusky Grouse habitat and therefore can be used to delineate areas for future population monitoring of Dusky Grouse in Montana.

The post Using an ensemble approach to predict habitat of Dusky Grouse (Dendragapus obscurus) in Montana, USA first appeared on Avian Conservation and Ecology.

Knowledge of space use provides insight into a species’ habitat requirements needed for conservation. Little is known about space use of the near threatened Kirtland’s Warbler (Setophaga kirtlandii) wintering in The Bahamas, and how the warbler’s home range size and core area overlap among individuals and vary with sex and age, food availability, winter season, and habitat characteristics. To address these knowledge gaps, we used radio telemetry to determine sedentary home range size (95% adaptive kernel), core area (50% AK), and overlap for 27 radio-tagged warblers during two winters on Eleuthera, The Bahamas. Warblers monitored for ~3 weeks each had a median sedentary home range of 8.87 ha (range: 0.53–118.50 ha) and a median core area of 1.04 ha (range: 0.05–12.69 ha). Foliage of the warbler’s principal fruit species (Lantana involucrata, Erithalis fruticosa, Chiococca alba) was present in more warbler core area plots than in outlier plots (telemetry fix points outside the 95% AK home range) or in random plots within the landscape. Both size of home range and core areas increased with site disturbance age – consistent with declines in fruit abundance associated with age of vegetation. Warbler core areas displayed little pairwise overlap in two sites, “RS” and “MR,” examined during October–December (RS, x̄ = 1.49%; MR, x̄ = 0.55%) and at a site in January–February (MR, x̄ = 3.32%), indicating areas of exclusive use or territoriality. In contrast, a fruit-rich site (“OH”) in March–April had higher pairwise overlap in core areas (OH, x̄ = 8.56%), which may have resulted in competition for fruit. Our findings re-emphasize the importance of conservation at a landscape scale if spatiotemporal variation in food resources increases or become more concentrated prior to migration with extreme weather due to global climate change.

The post Factors influencing home range size and overlap in nonbreeding Kirtland’s Warblers on Eleuthera, The Bahamas first appeared on Avian Conservation and Ecology.

Quantifying migratory connectivity and annual movement is key to sound conservation planning for migratory species. Hermit Warblers (Setophaga occidentalis) are an endemic-breeding species in the Pacific Northwest that winters in Mexico and the Central Americas. This species faces threats from mature forest loss and climate change throughout its range, but we know little about its migration ecology. To understand the annual movements and migratory connectivity of Hermit Warblers, we tracked 22 adult male Hermit Warblers from six breeding sites across the species’ breeding range using geolocators to examine migratory connectivity, spatiotemporal patterns, and migration routes. We found a high degree of mixing on the wintering grounds among birds from different breeding locations, indicating low migratory connectivity. However, birds breeding in Yosemite, the southernmost breeding location in our study, wintered farther east and south than birds from more northern breeding locations, providing weak evidence for potential chain migration. All birds showed much shorter and faster movements during spring migration than during fall migration. Birds arrived at breeding grounds from late April to mid-May and left breeding ranges from late June to mid-July. In fall, birds moved slowly from the breeding locations to montane regions in southern Oregon and California, which may indicate post-breeding molt before swiftly migrating to wintering grounds. Low migratory connectivity in this species implies that habitat and climate change across the broad wintering range may affect breeding populations throughout the species’ breeding range. A particularly compressed breeding schedule and departure of birds from the breeding grounds in early July may indicate that breeding is limited by a short window of favorable climatic conditions for breeding, which could signal heightened vulnerability under future climatic scenarios.

The post Annual migratory movement, apparent molt-migration, migration schedule, and diffuse migratory connectivity of Hermit Warblers first appeared on Avian Conservation and Ecology.

Although the White-headed Woodpecker (Dryobates albolarvatus) has been used as a management indicator species to guide forest management in the western U.S., basic information on the dispersal behavior of this species is currently unavailable. However, understanding dispersal can provide key information for management and conservation by revealing the mechanisms by which species colonize new areas and restored habitat. To address this information gap, we tracked the dispersal of juvenile White-headed Woodpeckers from their natal areas to their first spring home range in 2014–2018 and estimated dispersal distances using an interval-censored bias correction method with field observations and aerial telemetry surveys. We also compared habitat features between dispersal locations and spring home ranges. The median bias-corrected dispersal distance was 22.2 km in the fall (95% confidence interval [CI] = 16.4, 29.1 km), with 90% of woodpeckers dispersing >4.8 km (95% CI = 2.7, 8.3 km). The following spring, the median bias-corrected natal dispersal distance was 24.6 km (95% CI = 17.9, 32.3 km), while 10 individuals with full detection histories dispersed a median of 7.7 km to their first breeding locations (range 1.2–23.0 km). Our natal dispersal estimates for juvenile White-headed Woodpeckers were longer than those for most other woodpecker species studied to date. In addition, we found that woodpeckers settled in mid-elevation areas with greater variation in canopy cover compared to dispersal locations. There was no difference in ponderosa pine (Pinus ponderosa) basal area between dispersal tracks and spring home ranges. White-headed Woodpeckers are a species of conservation concern due to habitat loss in western North America, and active management in Washington state seeks to restore overstocked ponderosa pine forests to pre-settlement tree densities which could benefit this woodpecker. Our results inform conservation and forest management efforts by suggesting that dispersing juveniles have the capacity to travel long distances to colonize restored forests.

The post Bias-corrected natal dispersal estimates fill information gaps for White-headed Woodpecker conservation first appeared on Avian Conservation and Ecology.

The species-specific migratory patterns and strategies of many songbirds remain unknown or understudied, as research in animal ecology is biased toward the breeding period, with the fewest studies on the migratory period across taxa. Identifying large-scale spatiotemporal migratory patterns is challenging, as individuals within a species may vary in their migratory behavior and strategies. The Yellow Warbler (Setophaga petechia) is a Nearctic-Neotropical migrant that is relatively well studied during the breeding season, but its species-wide migratory patterns remain understudied. Our aim in studying Yellow Warbler movement ecology was to characterize temporal migration patterns during fall migration. We sought to determine the temporal migration pattern among breeding locations, as determined by the hydrogen stable isotope values in feather samples collected at disjunct (~2000 km) stopover sites in the Gulf of Maine (n = 50) and the Gulf of Mexico (n = 150). We used a similarity matrix to group individuals into a geographic cluster by breeding location, which was then used as the response variable in a modeling analysis. Our results provide evidence that Yellow Warblers exhibit an asynchronous, type 1 temporal migration pattern with southern breeding populations initiating migration prior to northern populations. Using hydrogen isotopes, we identified the temporal migration patterns between geographic clusters, representing an individual’s breeding location, and stopover sites along the Gulf of Maine and Gulf of Mexico, which fills a gap in understanding Yellow Warbler migration ecology.

The post Asynchronous movement patterns between breeding and stopover locations in a long-distance migratory songbird first appeared on Avian Conservation and Ecology.

Habitat loss is the primary driver of biodiversity decline worldwide, but it remains unknown how land-cover change and, in general, habitat loss impact many migratory species, such as the Rufous Hummingbird (Selasphorus rufus). Here, we gathered 5115 occurrence records for the Rufous Hummingbird from professional and citizen-science data sets and parameterized species distribution models with four bioclimatic variables and two Landsat satellite spectral reflectance bands. We calculated the population change and change in the potential distribution of the Rufous Hummingbird across its breeding range in the Pacific Northwest of North America over the last 36 yr (1985–2021). Back-casting habitat suitability predictions over time, we provide the first quantifications of breeding habitat change for the Rufous Hummingbird, which has exhibited precipitous declines over the past two decades. Furthermore, we evaluated links between modeled habitat suitability, population abundance, and trends with a route-level analysis of Breeding Bird Survey data. We found notable habitat loss occurring in Bird Conservation Regions along the Pacific coast where the species is most abundant (54% and 34% decreases in suitable habitat area), with habitat loss in coastal regions linked to population decline. In contrast, we detected habitat gains in regions along the interior, northeastern edges of the breeding range (160% and 85% increases in suitable habitat area). However, increasing suitability does not guarantee species colonization of new habitat. Our results indicate the need to further investigate drivers of habitat loss, such as intensive forestry and suppression of early seral habitat, along the Pacific coast. Our modeling approach can be applied to efficiently detect and quantify habitat loss over time for a variety of taxa.

The post Breeding habitat loss linked to declines in Rufous Hummingbirds first appeared on Avian Conservation and Ecology.

Hawaiian avifaunal communities have suffered irrevocable harm and significant threats remain for extant species. It is increasingly important to monitor and document bird density to improve our understanding of how remaining species respond to changing climate and emergent stressors. In this paper, we report annual densities (2003–2020) of two native and four non-native forest bird species in a region of Hawaiʻi Island lacking previous estimates. We estimated long-term population trends and short-term trajectories within a Bayesian framework. Our findings support previous studies that demonstrated the negative impact of ungulate browsing on forest bird habitat. We also note a detection of the Japanese Bush Warbler (Cettia diphone), a recently documented non-native species. The forest bird population trends presented here fill a regional gap and help extend the understanding of bird populations on Hawaiʻi Island.

The post Modeling forest bird population trends at U.S. Army Garrison Pōhakuloa Training Area, Hawaiʻi first appeared on Avian Conservation and Ecology.

Noise pollution can degrade the behavioral, physiological, and psychological health of humans and other creatures. We used breeding pairs of Eastern Bluebirds (Sialia sialis) to assess behavioral and reproductive responses to both chronic roadway noise and experimental intermittent playbacks of construction noise. Active nests in boxes placed near and far from large roads were randomly assigned as treatments or controls for experimental playbacks during incubation. Using temperature signatures from iButtons placed within nest cups we quantified certain female incubation behaviors (# and length of bouts, # of small temperature fluctuations, and total warming minutes per day) and hatching success was recorded for 40 nests in spring of 2019. Nests in quiet areas that received no additional playback treatments of construction noise had markedly higher nest success than any exposed to noise. Nests exposed to chronic traffic noise only, and quiet nests that received 3–4 days of construction noise had the lowest hatching success. Females in traffic-quiet nests increased restlessness (small temperature fluctuations) and experienced decreasing hatching success as the number of days of construction noise playback increased. Thus, birds choosing either quiet or noisy boxes had contrasting responses to bouts of construction noise. Other female incubation behaviors we could detect were unaffected by noise but changed in expected ways with seasonal progression. In sum, both types of noise can decrease hatch rate, but with intermittent noise this is likely due to female restlessness, or too many small drops in temperature to maintain optimal embryo development.

The post Intermittent and chronic noise impacts on hatching success and incubation behavior of Eastern Bluebirds (Sialia sialis) first appeared on Avian Conservation and Ecology.