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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 (λ) 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.
LAY SUMMARY
The adult loon population in northern Wisconsin has declined by 22% over the past 27 years.
Numbers of chicks and chick mass have declined significantly.
The population of young nonbreeders (floaters) has plummeted by 46%.
Despite these steep declines, there has been no measurable drop in the number of territorial pairs.
The hidden nature of the Wisconsin decline points out that floater populations can mask major drops in breeding populations and throws into question population trends in other loon populations, whose floater populations are largely unknown.
Sensory pollutants such as anthropogenic noise and night lighting now expose much of the world to evolutionarily novel sound and night lighting conditions. An emerging body of literature has reported a variety of deleterious effects caused by these stimuli, spanning behavioral, physiological, population, and community-level responses. However, the combined influence of noise and light has received almost no attention despite the co-occurrence of these stimuli in many landscapes. Here we evaluated the singular and combined effects of these stimuli on Western Bluebird (Sialia mexicana) reproductive success using a field-based manipulation. Nests exposed to noise and light together experienced less predation than control and light-exposed nests, and noise-exposed nests experienced less predation than control nests, yet overall nest success was only higher in noise-exposed nests compared to light-exposed nests. Although exposure to light decreased nestling body condition and evidence was mixed for the singular effects of noise or light on nestling size, those nestlings exposed to noise and light together were smaller across several metrics than nestlings in control nests. Our results support previous research on the singular effects of either stimuli, including potential benefits, such as reduced nest predation with noise exposure. However, our results also suggest that noise and light together can negatively affect some aspects of reproduction more strongly than either sensory pollutant alone. This finding is especially important given that these stimuli tend to covary and are projected to increase dramatically in the next several decades.
LAY SUMMARY
Noise and light pollution often occur together, but their combined influence on wildlife is poorly understood.
We manipulated traffic noise and artificial night lighting exposure at Western Bluebird nests.
Relative to control nests, those exposed to noise experienced lower nest predation and produced more fledglings whereas chicks in nests exposed to light took longer to fledge and had lower body condition.
Nests exposed to noise and light together produced smaller nestlings than control nests and, for some body measurements, those exposed to either noise or light alone.
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.
LAY SUMMARY
Miniature GPS tags were used to track breeding female Tree Swallows at agricultural sites.
Across agroecosystems, Tree Swallows selected more for wetland ponds than available in the landscape.
Swallows increasingly selected for wetland ponds with increasing distance from nests, consistent with central-place foraging theory.
Insect abundance and biomass tended to be greater in pond margins and non-crop vegetation (field margins or grasslands) than in croplands, but insect distribution patterns did not fully explain swallow habitat selection.
Piscivorous birds are the primary source of catfish (Ictalurus spp.) depredation at aquaculture facilities in northwestern Mississippi. Of particular concern is the Double-crested Cormorant (Phalacrocorax auritus), which can cost aquaculture producers millions of dollars annually through the depredation of cultured fish. Historical research conducted in the early 2000s estimated cormorant use of aquaculture ponds in the region, but aquaculture area has decreased by more than 70% since those estimates were made. With less aquaculture available, we predicted cormorant densities on aquaculture would be greater today than historically. Applying a similar methodology as in historical studies, we used aerial surveys to collect data on cormorants at night roosts and using catfish aquaculture ponds during 3 consecutive winter seasons, beginning in 2015. Although the mean annual number of cormorants at roosts in the Delta during our study was 64% less than historically, we found no significant change in densities on aquaculture, suggesting that aquaculture area is likely the factor influencing cormorant occurrence in northwestern Mississippi. During contemporary surveys we also measured the abundance of Great Blue Herons (Ardea herodias) and Great Egrets (A. alba) on the aquaculture clusters, and built predictive models of abundance relative to variables associated with forage at and surrounding the clusters. We found abundance of all 3 species was strongly related to the amount of aquaculture area both within and surrounding a cluster, although patterns varied by species. Cormorant abundance was also greater on clusters with proportionately more food fish (≥20 cm in length) than fingerlings (<20 cm) and was positively related to the proximity and size of night roosts. The relationships described here can be used by producers and wildlife managers to predict the abundance of these piscivorous birds at aquaculture facilities and to design efficient management plans to mitigate potential impacts of depredation and disease.
LAY SUMMARY
Mississippi contains ∼60% of all catfish production in the U.S., and bird depredation costs producers millions of dollars annually.
We studied how Double-crested Cormorants, Great Blue Herons, and Great Egrets use commercial catfish aquaculture in Mississippi.
However, catfish production in Mississippi has declined by over 70% since its peak in the early 2000s, raising questions regarding bird use, particularly by cormorants.
Does less aquaculture mean more cormorants per pond? Has the aquaculture decline affected cormorant abundance in the region, and is catfish aquaculture a driver of local bird abundance?
To address these questions, we compared surveys of cormorants from the early 2000s with contemporary surveys.
We found fewer cormorants in Mississippi today than in the past but cormorant density on ponds has not changed, suggesting a link to the amount of catfish ponds. Local abundance of all fish-eating birds surveyed was also related to the amount of catfish aquaculture.
The global breeding population of Eleonora's Falcon (Falco eleonorae) is distributed from the Canary Islands in the west, across the Mediterranean Sea, to Cyprus in the east. The remoteness of nesting colonies, which are predominantly located on sea cliffs and islets, renders breeding success estimation a challenging task, requiring a composite approach to assess each of the breeding stages. Early estimates of the breeding success of Eleonora's Falcon suggested that the Akrotiri colony in Cyprus had the lowest breeding success among all the colonies throughout the species' breeding range, at a level seemingly unsustainable, suggesting the colony might have been in danger of gradual extinction. Here we use a diversity of survey methods including boat, ground, and aerial surveys, with the incorporation of photography and photogrammetry, to reassess the breeding success and the effect of nest characteristics on the Eleonora's Falcon breeding population in Cyprus. During a 6-yr study, we found that Cyprus hosts ∼138 ± 8 breeding pairs and that breeding success equals 1.54 ± 0.85 fledglings per breeding pair, and thus is considerably higher than previous estimates. In addition, by analyzing temporal variation in breeding and nest characteristics, we found that early breeding and reuse of nests positively influence breeding success, but physical nest characteristics have a limited effect on colony productivity. The range of survey methods employed, as well as the array of photography techniques utilized, enhanced the efficiency and accuracy of this study, allowing us to overcome the challenge of inaccessibility of nesting cliffs.
LAY SUMMARY
In this study we reassessed the breeding success and population status of Eleonora's Falcon in Cyprus, a species nesting on inaccessible sea cliffs.
Low breeding success estimates from previous surveys suggested that the breeding population was unsustainable.
We used ground, aerial (drone), and boat surveys, combined with photogrammetry for nesting cliff 3-D modeling, to assess breeding success and nest site suitability.
Our results show that breeding success of Eleonora's Falcon is higher than previous estimates and that the population is stable.
The methods employed enhanced the efficiency and accuracy of our surveys, allowing us to overcome the challenge of inaccessibility of nesting cliffs.
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 Least Tern 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.
LAY SUMMARY
Birds that nest on public sandy beaches benefit from protective fencing and educational signs, but additional benefits may occur if volunteer stewards are stationed at the protected area.
I assessed whether the presence of stewards benefited nesting Least Terns by reducing human disturbance and increasing reproductive success at breeding colonies.
Audubon Mississippi staff monitored Least Tern colonies in coastal Mississippi from 2017 to 2019 while seasonal stewards observed the extent of disturbance at each colony.
Colonies with greater disturbance rates were less productive, and stewardship efforts benefited colonies by increasing nest hatch probability.
Posting stewards at breeding colonies is an effective management strategy for conserving Least Terns, although additional management actions are likely needed to increase chick survival.
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 ∼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.
LAY SUMMARY
Little is known about the post-fledging ecology and habitat requirements of many migratory songbirds.
We used VHF radio-transmitters to track 156 fledgling Golden-winged Warblers (Vermivora chrysoptera) from two subpopulations in Pennsylvania, USA, and describe their movements, habitat use, and habitat selection.
On average fledglings dispersed ∼750 m from nest sites by day 28 post-fledging with the maximum dispersal distance being 3.6 km.
Fledglings used all cover types but 85% of relocations occurred in stand initiation, stem exclusion, or mature forest uplands.
Habitat selection was directed primarily toward forest in the stand initiation stage, however fledglings in one landscape also selected for stem exclusion stands.
Managers should consider promoting additional forest stand age class diversity (especially forest in the stem exclusion stage) in areas proximate to Golden-winged Warbler nesting habitat to provide the structure necessary for fledglings.
Eastern Purple Martins (Progne subis 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.
LAY SUMMARY
Purple Martins are believed to have a high abundance of blood-feeding parasites (fleas, mites, and blowfly larvae) in their nests.
A current conservation policy recommends that nest box managers regularly remove and replace nest materials during the nestling phase to reduce parasite abundance. We tested the efficacy of this policy.
Nest replacements reduced flea and blowfly larvae abundance, but mite abundance rebounded quickly.
There was no difference in fledging rate, body mass, white blood cell count, or triglyceride or uric acid levels for nestlings with or without nest replacements.
Nestlings with nest replacements were less anemic and had a higher ratio of heterophils to lymphocytes.
Intense trapping of the critically endangered Yellow-crested Cockatoo (Cacatua sulphurea) for the international pet trade has devastated its populations across Indonesia such that populations of >100 individuals remain at only a handful of sites. We combined distance sampling with density surface modeling (DSM) to predict local densities and estimate total population size for one of these areas, Komodo Island, part of Komodo National Park (KNP) in Indonesia. We modeled local density based on topography (topographic wetness index) and habitat types (percentage of palm savanna and deciduous monsoon forest). Our population estimate of 1,113 (95% CI: 587–2,109) individuals on Komodo Island was considerably larger than previous conservative estimates. Our density surface maps showed cockatoos to be absent over much of the island, but present at high densities in wooded valleys. Coincidence between our DSM and a set of independent cockatoo observations was high (93%). Standardized annual counts by KNP staff in selected areas of the island showed increases in cockatoo records from <400 in 2011 to ∼650 in 2017. Taken together, our results indicate that KNP, alongside and indeed because of preserving its iconic Komodo dragons (Varanus komodoensis), is succeeding in protecting a significant population of Indonesia's rarest cockatoo species. To our knowledge this is the first time DSM has been applied to a critically endangered species. Our findings highlight the potential of DSM for locating abundance hotspots, identifying habitat associations, and estimating global population size in a range of threatened taxa, especially if independent datasets can be used to validate model predictions.
LAY SUMMARY
Yellow-crested Cockatoos are threatened by extinction due to illegal trapping for the pet trade. Komodo Island in Indonesia supports one of the largest remaining populations. The island is part of Komodo National Park, famous for its Komodo dragons. A 2006 survey indicated cockatoo numbers might have been declining.
In contrast to previous surveys we sampled the whole island instead of focusing on coastal valleys, which are known to harbor the highest cockatoo densities. We used distance sampling and density surface modeling, which allowed us to estimate how many cockatoos remained undetected and to produce a map of predicted cockatoo densities.
We estimate there are between 600 and 2,100 cockatoos on Komodo, most likely ∼1,100. Komodo National Park authorities also reported an increase in their annual counts of cockatoos from below 400 in 2011 to around 650 in 2017. Thus, the cockatoo population on Komodo Island is large and stable; Komodo National Park is successfully protecting its cockatoos.
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 (λ) and found that 80% (8/10 yr) of the observed λ 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 λ 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 λ 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.
LAY SUMMARY
Although montane birds are vulnerable to climate change, the effect of weather on their demography has seldom been investigated.
We examined the vital rates of the Green-backed Tit in a subtropical montane forest in Taiwan and constructed a model to simulate their population dynamics.
We found seasonal precipitation to be the critical factor driving population fluctuations.
High rainfall was related to decreased nest survival; typhoon-induced precipitation was associated with decreased adult survival.
As seasonal precipitation is expected to intensify under high greenhouse gas emission scenarios, this local population is unlikely to persist in the future. Hence, the species may become a conservation concern.
Benjamin J. Lagassé, Richard B. Lanctot, Mark Barter, Stephen Brown, Chung-Yu Chiang, Chi-Yeung Choi, Yuri N. Gerasimov, Steve Kendall, Joseph R. Liebezeit, Konstantin S. Maslovsky, Alexander I. Matsyna, Ekaterina L. Matsyna, David C. Payer, Sarah T. Saalfeld, Yoshimitsu Shigeta, Ivan M. Tiunov, Pavel S. Tomkovich, Olga P. Valchuk, Michael B. Wunder
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.
LAY SUMMARY
The East Asian–Australasian Flyway has more threatened and near-threatened migratory waterbird species than any other flyway in the world; however, developing flyway conservation plans has been challenging, in part due to limited information regarding population-specific migration patterns.
Four subspecies of Dunlin migrate and winter along the East Asian–Australasian Flyway. Each has a well-defined breeding range; their migration and winter ranges are poorly defined or unknown.
We assessed the migratory connectivity of 3 subspecies using data from 57 yr (1960–2017), which comprises more than 28,000 Dunlin banding records, 71 recaptures, and 747 band resightings.
Subspecific segregation likely occurs, with arcticola Dunlin wintering in Japan, and other arcticola, actites, and sakhalina Dunlin wintering in the Yellow and China seas. It is likely that ≥83% of arcticola Dunlin exhibit interannual site fidelity to specific wintering sites.
Our findings suggest that degradation of specific wetland areas may negatively affect particular individuals of a particular subspecies (or combination of subspecies) and could result in population declines.
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.
LAY SUMMARY
In landscapes where undisturbed, high-quality habitat is scarce, some birds may be forced to occupy low-quality habitat. Habitat restoration may provide more high-quality habitat.
The endangered population of Yellow-breasted Chats in British Columbia increased in abundance from 2002 to 2014 in response to habitat restoration efforts. We investigated 2 questions: (1) Do chats prefer to nest in areas with certain vegetation characteristics? and (2) What effects do vegetation characteristics and parasitism by Brown-headed Cowbirds, which lay their eggs in chat nests, have on chat reproductive success?
Settlement patterns indicated that chats prefer to occupy breeding territories with high shrub cover. However, Brown-headed Cowbirds parasitized half of all chat nests, and whether or not a nest was parasitized was more important than vegetation characteristics in determining how many chat fledglings were produced.
Habitat restoration efforts provided more suitable habitat for this recovering population but did not reduce how often chat nests were parasitized. Chats in this population still have relatively high reproductive success and therefore are not as vulnerable to cowbird parasitism as other songbirds.
Migration is a period of high activity and exposure during which risks and energetic demand on individuals may be greater than during nonmigratory periods. Stopover locations can help mitigate these threats by providing supplemental energy en route to the animal's end destination. Effective conservation of migratory species therefore requires an understanding of use of space that provides resources to migratory animals at stopover sites. We conducted a radio-telemetry study of a short-distance migrant, the American Woodcock (Scolopax minor), at an important stopover site, the Cape May Peninsula, New Jersey. Our objectives were to describe land-cover types used by American Woodcock and evaluate home range habitat selection for individuals that stopover during fall migration and those that choose to overwinter. We radio-marked 271 individuals and collected 1,949 locations from these birds (0–21 points individual–1) over 4 yr (2010 to 2013) to inform resource selection functions of land-cover types and other landscape characteristics by this species. We evaluated these relationships at multiple spatial extents for (1) birds known to have ultimately left the peninsula (presumed migrants), and (2) birds known to have remained on the peninsula into the winter (presumed winter residents). We found that migrants selected deciduous wetland forest, agriculture, mixed shrub, coniferous wetland forest, and coniferous shrub, while wintering residents selected deciduous wetland forest, coniferous shrub, and deciduous shrub. We used these results to develop predictive models of potential habitat: 7.80% of the peninsula was predicted to be potential stopover habitat for American Woodcock (95% classification accuracy) and 4.96% of the peninsula was predicted to be potential wintering habitat (85% classification accuracy). Our study is the first to report habitat relationships for migratory American Woodcock in the coastal U.S. and provides important spatial tools for local and regional managers to support migratory and winter resident woodcock populations into the future.
LAY SUMMARY
Stopover sites provide habitat for migratory animals to rest and refuel before continuing migration, making these areas important for species' conservation.
We used radio-telemetry to assess American Woodcock stopover and wintering habitat selection on the Cape May Peninsula, New Jersey.
Short-term migrants used a greater variety of land-covers than winter residents, although both selected deciduous wetland forest and sites in close proximity to fields.
Less than 10% of the Cape May Peninsula provides stopover or wintering habitat for American Woodcock, highlighting the importance of conserving these important but potentially limited resources.
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 ∼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.
LAY SUMMARY
Private timber lands can provide important habitat for birds, especially when landowners create open forest conditions.
We surveyed birds and vegetation in southeastern U.S. loblolly pine forests in 2017 and 2018.
Forests managed differently, for example with different numbers of burns, had different structures and compositions and supported different bird totals—both in numbers and types of species.
We identified varying factors for different species' abundances from stand basal area to the forest extent (≤5 km).
The Rusty Blackbird (Euphagus carolinus) is a widespread, uncommon migrant that has experienced heavy population declines over the last century. This species can spend over a quarter of their annual cycle on migration, so it is important to determine their habitat requirements during stopover events to inform effective conservation planning. We assessed their habitat selection at an important stopover site in northern Ohio during both fall and spring migration. Since stopover habitat selection is scale-dependent, we investigated both patch-scale (between patches) and fine-scale (within a patch) selection using radio telemetry to locate foraging and roosting flocks, and compared habitat variables between used and available points across the study site. At the patch scale, we found that birds preferred dogwood–willow swamp, low-lying forest patches, and areas of greater habitat complexity for foraging in both seasons. At the fine scale, spring migrants foraged closer to habitat edges than random, and preferred areas with more wet leaf litter and shallow water, and less grass cover. Fall migrants also preferred shallow water and leaf litter cover, and avoided areas with dense grass, forbs, and herbaceous shrub cover. By contrast, birds consistently roosted in dense stands of emergent Phragmites or Typha marsh, suggesting that the best stopover or staging sites are those with a matrix of different wetland habitats. Although the migratory range of Rusty Blackbirds is currently dominated by agricultural development, our results suggest that fragmented landscapes can still provide adequate habitat for migrants if the available land is managed for a variety of wet habitat types.
LAY SUMMARY
The Rusty Blackbird is a widespread, uncommon migrant that has experienced heavy population declines over the last century.
Rusty Blackbirds can spend over a quarter of the year on migration, so it is important to determine their habitat requirements during stopover events to inform conservation planning.
We assessed their habitat selection at 2 spatial scales at an important stopover site in Ohio during fall and spring migration, using radio telemetry to locate foraging and roosting flocks.
At the patch scale, we found that Rusty Blackbirds preferred dogwood–willow swamp, flooded forest patches, and areas of habitat complexity for foraging.
At the fine scale, birds foraged close to habitat edges, and preferred areas with more wet leaf litter and shallow water, while avoiding dense grass, forbs, and herbaceous shrub cover.
By contrast, Rusty Blackbirds consistently roosted in dense stands of emergent marsh, suggesting that the best stopover sites are those with several different wetland habitats.
SPECIAL FEATURE: ADVANCES IN NEOTROPICAL ORNITHOLOGY
Of the approximately 716 bird species that breed in North America, 386 (54%) are considered Nearctic–Neotropical migrants by the U.S. Fish and Wildlife Service. In the past 50 yr, scores of these migratory species, including some once considered common, have declined dramatically. Nearctic–Neotropical migrants normally spend 6–8 months in tropical habitats, making the identification, availability, and management of Neotropical habitats critical issues for their conservation. Yet, for most species, complete and nuanced information about their use of tropical habitats and the relative effects of breeding vs. wintering conditions on survival, productivity, and population trends is not available, though many studies point to Neotropical overwintering habitats as being a strong driver of population change. Particularly important for long-distance Nearctic–Neotropical migrants is an understanding of how “carry-over effects” arise and influence population trends when conditions on wintering grounds and tropical stopover areas affect subsequent reproductive performance on breeding grounds. For example, why some species show strong carry-over effects from tropical habitats while others do not is not fully understood. In recent years, many studies have offered insights into these issues by taking advantage of new scientific methods and technological innovations. In this review, we explore threats facing North American breeding birds that migrate to the Neotropics, summarize knowledge of habitat selection and use on the wintering grounds, describe how conditions at one point in the annual cycle may manifest in subsequent seasons or life history stages, and discuss conservation concerns such as climate change and the potential for phenological mismatch.
LAY SUMMARY
More than half of the bird species that breed in North America, representing billions of birds, migrate to the Neotropics.
In the past 50 years, scores of these species have declined dramatically.
Migratory birds normally spend 6–8 months in tropical habitats, making the conservation of these species an international challenge. Yet, for most species, complete and nuanced information about their use of tropical habitats and the relative effects of breeding vs. wintering conditions on survival, productivity, and population trends is not available.
Accelerating climate change is adding to the urgency of our gaining an understanding of the full annual and migratory cycle of these birds.
In recent years, many studies have offered insights into these issues by taking advantage of new scientific methods and technological innovations.
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.
LAY SUMMARY
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.
We provide a comprehensive review of current knowledge of vulture social behavior and the evolutionary and ecological roots of their social systems.
Within this social framework, we discuss aspects as diverse as vulture breeding and mating systems, foraging techniques, social hierarchies, territorial and gathering behavior, and interspecific interactions.
Overall, we stress that advancing our socio-ecological understanding of the rich social life of vultures is critical to harmonize their conservation in this rapidly changing world.
Samantha G. Robinson, Daniel Gibson, Thomas V. Riecke, James D. Fraser, Henrietta A. Bellman, Audrey DeRose-Wilson, Sarah M. Karpanty, Katie M. Walker, Daniel H. Catlin
Evaluating population-level responses to conservation action following large-scale disturbance can improve the efficacy of future habitat conservation measures. In October 2012, Hurricane Sandy storm surges cleared vegetation and opened inlets through the barrier islands, Fire Island and Westhampton Island, New York, creating Piping Plover (Charadrius melodus) habitat. Storm effects prompted an island-wide stabilization project, which had the potential to negatively affect novel Piping Plover habitat. Certain sections of Fire Island were designed to create and/or improve habitat (hereafter, restoration areas) to mitigate possible habitat loss or degradation. Since Piping Plovers in New York appear to be habitat-limited, we anticipated positive population growth following habitat creation. From 2013 to 2018, we captured and banded 152 adults and 353 chicks, and monitored 279 nests and 160 broods. We developed an integrated population model to assess demographic processes in response to hurricane created-habitat (2013–2018) and the creation of restoration areas (2015–2018). We observed positive population growth in 3 of 5 yr, and overall growth throughout the period ( = 1.13). Immigration and reproductive output were correlated with population growth (r = 0.92 [95% CI: 0.22 to 0.98] and 0.84 [95% CI: –0.47 to 0.95], respectively). Compared with the rest of the study area, restoration areas had higher chick survival, and lower nest survival and after second-year site fidelity. The result was population growth in restoration areas ( = 1.14) similar to the whole study area. In the short term, restoration areas seemed to mimic natural Piping Plover habitat. Vegetation removal, an important process in renewing natural Piping Plover habitat, likely will be necessary to maintain habitat suitability. Efforts to increase immigration of new breeding adults into the system, and to improve reproductive output, primarily by habitat creation or maintenance, are likely to have the greatest local effect on population growth.
LAY SUMMARY
Despite being listed under the Endangered Species Act for more than 30 yr, and intensive management, Piping Plovers on the Atlantic Coast have not met population recovery goals across much of their breeding range.
Hurricane Sandy increased available nesting habitat (dry sand) by over 150%. Following Hurricane Sandy, we monitored a population of individually marked birds on Fire Island and West Hampton Island, New York, for 6 yr. The area monitored included restored habitat, to evaluate the effectiveness of Piping Plover targeted habitat management.
The population increased 90% in the 6 yr following Hurricane Sandy, primarily because of immigrant adults, and local reproductive success. The reproductive output and population growth in restoration areas were similar to the rest of the study area.
Overall, Hurricane Sandy habitat creation was positive for this local plover population.
Efforts to allow future hurricane storm surges to create habitat, along with continued management, will improve long-term population persistence.
Conservation efforts are shaped by individual and collective human behaviors, cultural norms and values, economic pressures, and political and organizational structures. As such, the conservation social sciences—disciplines that draw on social science theories and approaches to improve conservation efforts—can play a vital role in advancing the science and practice of bird conservation. We connect the rich, ongoing discussion about the vital role of the conservation social sciences to the specific context of bird conservation and make an argument for the importance of proactive inclusion of these sciences in ornithological societies. First, we introduce the conservation social sciences and illustrate how they can improve the design and implementation of conservation programs and policies for birds. Drawing on discussions from a symposium we organized at the 2019 American Ornithological Society (AOS) annual meeting, we encourage the AOS to make institutional changes that could further support the inclusion of conservation social sciences. These changes ideally would include a working group, conference plenaries and themes, and high-quality social science publications, along with support and encouragement for ornithologists and bird conservationists to partake in trainings and collaborate with social scientists. Strategies for how to do so effectively can be adapted from other conservation societies that have paved the way for disciplinary inclusivity.
LAY SUMMARY
The conservation social sciences investigate how people think and act in relation to biodiversity, including birds and the habitats that support them.
Application of conservation social science findings can improve the effectiveness of bird conservation.
he American Ornithological Society and its members can take specific steps to facilitate integration of the conservation social sciences with ornithology.
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