Avian Conservation and Ecology最新文献

Understanding an animal’s diet is a crucial component of conservation, but diet data are often labor intensive to collect and are frequently scarce. Atlantic Puffins (Fratercula arctica; hereafter Puffins) are vulnerable to global extinction and have declined in some parts of their UK and Irish range. Differences in population trajectories may relate to diet, but Puffin diet data are currently only collected at a handful of colonies. We explored whether citizen science could address this data gap by inviting visitors to Puffin colonies in 2017 to submit their photographs of Puffins carrying prey. In total, 602 people submitted 1402 images from 35 colonies. We identified the species group, size, and number of prey items in each bill load. Photograph quality was excellent, with 89% of birds in images providing useable diet information. In total 11,150 prey items were counted and measured from 1198 Puffins across 27 colonies. We demonstrated a lack of bias in the sample of photos provided by citizen scientists and described how Puffin chick diet varies in prey composition, prey length, number of prey per bill load, and load biomass over large spatial scales and throughout the breeding season. The diet of Puffin chicks from regions where severe declines have occurred, most notably Shetland, were characterized by a lower prey biomass, higher numbers of fish per load, and a high proportion of small, transparent sandeels consistently through the season. By contrast, in regions where Puffin populations are thought to be increasing, load biomass was high, the number of prey per load low, and larger non-transparent sandeels were the dominant prey, which persisted right through the breeding season. Results from our study show colonies and regions where birds may be expending more effort (collecting more prey items) for lesser returns (lower load biomass) and emphasize the value of collecting diet data across large spatial scales.

The post Spatial and within-season variation in the diet of a declining seabird described through digital photography and citizen science first appeared on Avian Conservation and Ecology.

Long-billed Curlews (Numenius americanus) are declining throughout North America, and the loss of grassland breeding habitat is one of the primary threats to the species. Intermountain West, in particular, has been identified as the most important region in North America for breeding curlews. Nevertheless, the density and abundance of Long-billed Curlews in this region is not well understood. Lands managed for military training can provide habitat for wildlife species of conservation concern, and increasingly these lands are becoming relevant to sustaining biodiversity. We conducted point count surveys of Long-billed Curlews on Department of Defense lands in the Columbia Basin near Boardman, Oregon, USA during two consecutive breeding seasons. We used multinomial-Poisson mixture models to estimate detection probability and density of curlews and to investigate environmental correlates of those metrics. Mean detection probability at a distance of 400 m was 0.45 and 0.61 in 2015 and 2016, respectively. In 2015, the clarity of skies increased detection probability, but in 2016, none of the variables we measured influenced detection probability. Mean predicted density was 3.3 (95% confidence interval: 2.4–4.7) and 1.8 (1.2–2.7) curlews/km² in 2015 and 2016, respectively. In both years, curlew density was higher in lower-elevation or topographically smoother areas. Estimated abundance of curlews in the study area was 639 (456–912) and 350 (237–520) birds in 2015 and 2016, respectively. The number of curlews appeared to fluctuate across the two years of our study, a demographic trend that may have been influenced by a wildfire in our study area in June 2015. The results of our study indicate that federal grasslands, including areas where military operations are conducted, can provide conservation benefit to breeding Long-billed Curlews.

The post Abundance of Long-billed Curlews on military lands in the Columbia Basin first appeared on Avian Conservation and Ecology.

Effective conservation management relies on survey methods that accurately represent the biological communities being monitored. Here, we describe a novel approach using long-duration acoustic recordings to estimate abundance of a threatened wetland bird, the Australasian Bittern (Botaurus poiciloptilus). Whereas acoustic monitoring enables a large increase in effort compared to traditional on-site monitoring, e.g., triangulation surveys, it is difficult to estimate the number of individuals of a target species in acoustic recordings. We describe a semi-automated approach to estimate bittern abundance at four sites in the Barmah-Millewa Forest of southern Australia using single-channel, long-duration recordings. Our approach leveraged several known characteristics of bittern calling behavior. We obtained abundance estimates that are larger than those previously found using triangulation surveys at the same site. This is primarily attributed to our ability to find the peak calling hours in a long-duration recording, which does not require the training of a machine-learning call-recognizer. If the method we describe is performed in a consistent, standardized manner, it can identify population trends, which is an important outcome for a threatened species. Our method should be suitable for other furtive wetland species with a similar call structure or frequency range.

The post A new method to estimate abundance of Australasian Bittern (Botaurus poiciloptilus) from acoustic recordings first appeared on Avian Conservation and Ecology.

Effective conservation planning for species of concern requires long-term monitoring data that can accurately estimate population trends. Supplemental or alternative methods for estimating population trends are necessary for species that are poorly sampled by traditional breeding bird survey methods. Counts of migrating birds are commonly used to assess raptor population trends and could be useful for additional taxa that migrate diurnally and are difficult to monitor during the breeding season. In North America, the Common Nighthawk (Chordeiles minor) is challenging to detect during comprehensive dawn surveys like the North American Breeding Bird Survey and is considered a species of conservation concern because of steep population declines across its range. We conducted standardized evening counts of migrating Common Nighthawks at a fixed survey location along western Lake Superior each autumn from 2008 to 2022. To document peak migration activity, counts spanned ~3 hours each evening from mid-August to early September for a mean of 19.4 ± 2.4 days. These count data were then used to assess the effects of weather on daily counts and high-count days and to calculate population trends over this 15-year period. We used generalized linear mixed effects models to determine the relationship between daily counts and high-count days (i.e., ≥1000 migrating nighthawks) and weather variables. Additionally, using our 15-year dataset, we calculated a geometric mean passage rate that accounted for annual differences in weather to estimate count trends. Annual counts averaged ~18,000 (min = 2514, max = 32,837) individuals and high-count days occurred 56 times throughout the course of the study. Model results indicated lighter, westerly winds and warmer temperatures were associated with higher daily counts and greater probability of a large migratory flight. Results from the trend analyses suggest stable or non-significantly increasing trends for Common Nighthawks during this monitoring period; however, the trend models explained a relatively low percentage of the variation in the counts. Results from a power analysis suggest that continued monitoring efforts and adjustments with weather covariates will be necessary to effectively use visible migration count data to estimate Common Nighthawk trends. Establishing annual monitoring programs that use standardized visual counts to document Common Nighthawk migration at key sites across North America may provide supplemental information useful for population trend estimates of this species. Therefore, we advocate for the use of visible migration counts to monitor Common Nighthawks in North America and emphasize the value of long-term monitoring efforts.

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Beach habitat is increasingly degraded and disturbed, and many species of Larids (gulls, terns, and skimmers) have adapted to nesting on gravel rooftops. In the southeastern United States, the most common rooftop nester is the Least Tern (Sternula antillarum), and rooftop tern colonies are generally as productive as beach colonies. One problem with rooftop nesting is that chicks often fall from the roofs and will likely die if not rescued. Fallen chicks can be taken to wildlife rehabilitators and if they survive, be released on their own, but they will not receive the substantial pre- and post-fledgling parental care that Least Tern parents provide. We explored the success of placing chicks back on rooftops until they fledge and are able to travel to a staging beach. To determine long-term survival of these birds, from June 2011- July 2019, we uniquely banded 168 fallen Least Tern chicks in the Tampa Bay, Florida (USA) region and placed them back on the rooftops. From 2011-2022, we resighted banded birds on beaches, piers, and rooftops throughout Florida during the breeding season. We used the Cormack-Jolly-Seber model in Program Mark to estimate survival of juveniles and adults. The base model, where time was held constant for apparent survival and of both age classes and recapture rates, was the most parsimonious. We resighted 50 out of the 167 banded adult Least Terns a total of 347 times from 2012-2021. Apparent survival for fallen juvenile Least Terns was 0.387 ± 0.049 and 0.819 ± 0.032 for adult terns. There are no other studies of survival for juvenile Least Terns, but a closely related species had a slightly higher apparent survival. Adult survival in our study was comparable to that found in other similar Least Tern studies. This indicates that putting fallen Least Tern chicks back onto rooftops is a sound management strategy and should be explored for other species of seabirds.

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Urbanization can influence many environmental factors that can affect the condition, immunity, and gut microbiota of birds. Over the past several decades, the Galápagos Islands of Ecuador have experienced increasing human activity, which has led to recent changes in the morphology, gut microbiota, and immunity of Darwin’s finches. However, these traits have not been characterized before the exponential growth of human population size and tourist visitation rates, i.e., before 2009. The goal of this study was to determine the effect of land use on the fecal microbiota, immune response, and body measurements of Darwin’s finches in 2008, at a time of rapidly increasing human activity on the islands. Specifically, we compared fecal microbiota (bacterial diversity, community structure and membership, and relative abundance of bacterial taxa), proxies of immunity (lysozyme activity and haptoglobin, complement antibody, and natural antibody levels), and body measurements (body mass and condition, tarsus length) across undeveloped, agricultural, and urban areas for medium ground finches (Geospiza fortis) and small ground finches (G. fuliginosa). Lysozyme activity was lower and observed bacterial species richness was higher in urban areas compared to non-urban areas across both finch species. In medium ground finches, four genera (Methylobacterium-Methylorubrum, Escherichia-Shigella, Brucella, and Citrobacter spp.) were higher in urban areas compared to undeveloped areas. In small ground finches, Paucibacter, Achromobacter, Delftia, Stenotrophomonas, and Brucella spp. had higher relative abundances in undeveloped and agricultural areas whereas the genus Cutibacterium was more abundant in finches from urban and agricultural areas than in finches from undeveloped areas. Medium ground finches were smaller in undeveloped areas compared to the other two areas, but body mass of small ground finches did not differ across areas. Our results suggest that human activity can have an impact on immune measures and gut microbiota of Darwin’s finches.

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Forest thinning on public lands in the Pacific Northwest USA is an important tool for restoring diversity in forest stands with a legacy of simplified structure from decades of intensive management for timber production. A primary application of thinning in young (< 50-year-old) stands is to accelerate forest development to mitigate loss of late-seral habitat to decades of logging. However, thinning may have short-term negative effects for some species associated with mature forest that are expected to benefit from the practice over the long term. An increased risk of nest predation is a primary concern to managers charged with stewardship of habitat for the federally threatened Marbled Murrelet (Brachyramphus marmoratus), a species that nests in older forests. Predation by corvids is the greatest cause of nest failure for the Marbled Murrelet, and corvids are known to respond positively to forest disturbance, but quantitative information is lacking on the potential impacts of thinning on risk of nest predation. We investigated the response of two common corvid nest predators, Steller’s Jay (Cyanocitta stelleri) and Canada Jay (Perisoreus canadensis), to variation in thinning intensity in young forest (< 50 years old) using data from a long-term silviculture experiment. We used a Before-After-Control-Impact (BACI) design, linear mixed modeling, and occupancy modeling to quantify differences in corvid observation rates among varying levels of thinning intensity, and to assess changes in jay response over more than a decade following thinning. We found an increase in observation rates of both species in the heavily thinned treatment during the first 5 to 7 years following thinning, and some evidence of a short-term increase in Steller’s Jay activity in the thinning-with-gaps treatment. Neither jay species responded to the least intensive thinning treatment, which reduced average canopy cover by < 30%. By approximately a decade after thinning, observation rates of jays did not differ between unthinned controls and any of the thinning treatments. Incorporating our quantitative information into landscape-level planning can help managers balance short- and long-term conservation goals.

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In the Great Lakes Region, Sharp-tailed Grouse (Tympanuchus phasianellus) use open habitats of grass and brush that require frequent management. Wildlife managers expressed concern that Sharp-tailed Grouse were not responding to management throughout the year, so we examined responses to prescribed fire and mechanical treatment (mowing or shearing) conducted during the fall. We surveyed Sharp-tailed Grouse use and vegetation at 15 mechanical treatments, 10 prescribed burns, and 25 control sites in a before-after-control-impact-paired design. We surveyed Sharp-tailed Grouse use before management, and one week, one month, one year, and three years after management by conducting fecal pellet surveys along transects at each site. Sharp-tailed Grouse responses, as indicated by differences between fecal pellet counts at treatments and paired controls during each survey, increased following prescribed fire, but did not change after mechanical treatments. However, increased Sharp-tailed Grouse use following prescribed fire was temporary, thus management should be conducted at least once every three years at each site. Changes in vegetation metrics at managed sites were also temporary and most metrics returned to pre-treatment levels after one year, although shrub height at sites that received mechanical treatments and the forb response following prescribed fire persisted for > 3 years. We suggest that fall prescribed fire is more effective at increasing Sharp-tailed Grouse use of sites than fall mechanical treatment, which could be due to differences in vegetation responses, site size, landscape context, or cues produced by fire that attract Sharp-tailed Grouse. However, mechanical treatments maintain Sharp-tailed Grouse habitat, and without management, unchecked woody encroachment reduces habitat. Targeting mowing and shearing at sites known to be used by Sharp-tailed Grouse may prioritize management activities to sites that will have the most impact. Prescribed fire and mechanical treatments produced different Sharp-tailed Grouse and vegetation responses in the fall and should be used to address different management objectives.

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The migration phenology of many bird species has changed over the past few decades, but whether such changes lead to changes in the nesting phenology remains little known. Studying bird nesting in the boreal forest comes with challenges because of the large size of this biome. We evaluated songbird nesting phenology for the past 25 yrs in a boreal forest in eastern Canada, Forêt Montmorency. We used the observation of food transport in adults as an index of parental status, considering the imperfect detection of this status through hierarchical models of site occupation. We estimated annual phenology as the Julian date of the inflection point of the logistic fit of proportion of sites with parental activity as a function of Julian date. Contrary to expectations related to the advance of spring migration in North America, models did not show an advancement in the nesting season. Models showed that passerines can move their nesting date back or forward by 1 to 9 d. Models suggested that short-distance migrants delayed their nesting date by 2 wks against 1 mo for long-distance migrants. These results show the capacity of songbirds to adjust their nesting time and remind us of the value of regional studies when we are interested in reproductive phenology.

The post Nesting phenology of migratory songbirds in an eastern Canadian boreal forest, 1996–2020 first appeared on Avian Conservation and Ecology.

Blackpoll Warblers (Setophaga striata) have declined precipitously according to the North American Breeding Bird Survey, but that survey’s coverage of the boreal breeding range is limited. Migration monitoring offers an attractive tool for additional assessment because migrants from inaccessible portions of the breeding range are included in counts. However, for site-specific trends to be combined into regional or range-wide population trends, the breeding ground origin of the migrants counted at each site must be known. Blackpolls have a loop migration pattern in which spring and fall migrants follow different paths, but very little is known about population-specific routes within North America. We used stable hydrogen isotope assays of tail feathers (δ²H_f, 4th rectrix) and wing-length measurements from migration monitoring sites across Canada and the northeastern United States to broadly delineate breeding/natal origins of blackpolls captured at those sites. Blackpolls captured on spring migration in southern Ontario and western Quebec had characteristics expected of birds from breeding range west of the Great Lakes. These birds travel northward from the eastern Gulf of Mexico to Canada east of the Great Lakes before turning westward to reach their final destination between northwestern Ontario and eastern portions of the Northwest Territories. Many birds sampled at Great Lakes sites prior to 2010, but not thereafter, had δ²H_f and wing-length characteristics expected of breeding range in eastern Canada, suggesting differential rates of population change among regions. Estimates of migratory connectivity indicated considerable mixing of populations from different portions of the breeding range during migration. Our results both corroborate and refine the known clockwise loop migration pattern, provide new insight into spring migration routes across North America, and provide a foundation for incorporating breeding ground origins into estimations of range-wide population trends based on standardized migration counts.

The post Feather isotopes (δ²H_f) and morphometrics reveal population-specific migration patterns of the Blackpoll Warbler (Setophaga striata) first appeared on Avian Conservation and Ecology.