Changes in avian species composition following surface mining and reclamation along a riparian forest corridor in southern Indiana

Data on the response of bird communities to surface mining and habitat modification are limited, with virtually no data examining the effects of mining on bird communities in and along riparian forest corridors. Bird community composition was examined using line transects from 1994 to 2000 at eight sites within and along a riparian forest corridor in southwestern Indiana that was impacted by an adjacent surface mining operation. Three habitats were sampled: closed canopy, riparian forest with no open water; fragmented canopy, riparian forest with flood plain oxbows; and reclaimed mined land with constructed ponds. Despite shifts in species composition, overall bird species richness, measured as the mean number of bird species recorded/transect route, did not differ among habitats and remained unchanged across years. More species were recorded solely on mined land than in either closed forest or forested oxbow habitats. Mined land provided stopover habitat for shorebirds and waterfowl not recorded in other habitats, and supported an assemblage of grassland-associated bird species weakly represented in the area prior to mining. A variety of wood warblers and other migrants were recorded in the forest corridor throughout the survey period, suggesting that, although surface mining reduced the width of the forest corridor, the corridor was still important habitat for movement of forest-dependent birds and non-resident bird species in migration. We suggest that surface mining and reclamation practices can be implemented near riparian forest and still provide for a diverse assemblage of bird species. These data indicate that even narrow (0.4 km wide) riparian corridors are potentially valuable in a landscape context as stopover habitats and routes of dispersal and movement of forest-dependent and migratory bird species.     

Migration routes and stopover sites of Black-necked Cranes determined by satellite tracking

ABSTRACT.   Because their breeding and wintering areas are in remote locations, little is known about the biology of Black-necked Cranes ( Grus nigricollis ), including their migratory behavior. Using satellite telemetry, we monitored the migration of Black-necked Cranes ( N = 6) in China to determine migration routes and the location of stopover sites. From 2005 to 2007, four cranes were tracked during two spring migrations and one fall migration, one was tracked during one spring and one fall migration, and one was tracked during one spring migration. On average, the cranes made seven flights over a 5-d period to migrate 651 km to breeding areas in the spring. In the fall, birds averaged six flights in 5 d to migrate 694 km. The routes traveled by cranes during spring and autumn migration were similar. Both the migration distances and duration of migration are the shortest reported for any crane species to date. Most stopover sites were in areas along rivers and close to wetlands in the Daliang Mountains and the Ruoergai Plateau. Conservation measures are needed to reduce habitat loss (wetland and pasture) in the Daliang Mountains and establish a reserve for stopover sites in the Ruoergai marshes, such as Longriba and Bai River in Hongyuan County.     

Multiple habitat use by declining migratory birds necessitates joined‐up conservation

Many species depend on multiple habitats at different points in space and time. Their effective conservation requires an understanding of how and when each habitat is used, coupled with adequate protection. Migratory shorebirds use intertidal and supratidal wetlands, both of which are affected by coastal landscape change. Yet the extent to which shorebirds use artificial supratidal habitats, particularly at highly developed stopover sites, remains poorly understood leading to potential deficiencies in habitat management. We surveyed shorebirds on their southward migration in southern Jiangsu, a critical stopover region in the East Asian Australasian Flyway (EAAF), to measure their use of artificial supratidal habitats and assess linkages between intertidal and supratidal habitat use. To inform management, we examined how biophysical features influenced occupancy of supratidal habitats, and whether these habitats were used for roosting or foraging. We found that shorebirds at four of five sites were limited to artificial supratidal habitats at high tide for ~11–25 days per month because natural intertidal flats were completely covered by seawater. Within the supratidal landscape, at least 37 shorebird species aggregated on artificial wetlands, and shorebirds were more abundant on larger ponds with less water cover, less vegetation, at least one unvegetated bund, and fewer built structures nearby. Artificial supratidal habitats were rarely used for foraging and rarely occupied when intertidal flats were available, underscoring the complementarity between supratidal roosting habitat and intertidal foraging habitat. Joined‐up artificial supratidal management and natural intertidal habitat conservation are clearly required at our study site given the simultaneous dependence by over 35,000 migrating shorebirds on both habitats. Guided by observed patterns of habitat use, there is a clear opportunity to improve habitat condition by working with local land custodians to consider shorebird habitat requirements when managing supratidal ponds. This approach is likely applicable to shorebird sites throughout the EAAF.     

Precise direct tracking and remote sensing reveal the use of forest islands as roost sites by Purple Martins during migration

Direct tracking methods in combination with remote sensing data allow examination of habitat use by birds during migration. Species that roost communally during migration, such as some swallows, form large aggregations that can attract both avian and terrestrial predators. However, the extent to which they might use patchy habitats that could reduce predation risk during migration is unknown. We tested the hypothesis that Purple Martins (Progne subis) use forest islands (patches of suitable forest habitat surrounded by unsuitable habitat) as roost sites during migration between breeding sites in North America and overwintering sites in South America. We used high‐precision (< 10 m), archival GPS units deployed and retrieved during the 2015 and 2016 breeding seasons, respectively, at 12 colonies located across eastern North America. We found that Purple Martins roosted in forest islands more often than expected based on availability during both spring and fall migration. Despite an apparent association with urban habitats by Purple Martins based on observational and radar data in North America during the fall, the roost locations we identified during spring and fall migration were not more closely associated with urban areas than random locations. The use of forest islands during both spring and fall migration suggest that Purple Martins may use these habitats to reduce predation risk during migration. Our results suggest that some species of birds may use similar habitats as stopover sites during migration and that patches of forest habitat may be important conservation targets for Purple Martins and other species. Identifying habitat use during migration represents an important advance in support of full annual‐cycle conservation of Purple Martins and other migratory species with declining populations.     

No Habitat Selection during Spring Migration at a Meso-Scale Range across Mosaic Landscapes: A Case Study with the Woodcock (Scolopax rusticola)

Success of migration in birds in part depends on habitat selection. Overall, it is still poorly known whether there is habitat selection amongst landbird migrants moving across landscapes. Europe is chiefly covered by agro-forestry mosaic landscapes, so migratory species associated to either agricultural landscapes or woodland habitats should theoretically find suitable stopover sites along migration. During migration from wintering to breeding quarters, woodcocks (Scolopax rusticola) tagged with PTT satellite-tracking transmitters were used to test for the hypothesis that migrants associated to agro-forest habitats have no habitat selection during migration, at a meso-scale level. Using a GIS platform we extracted at a meso-scale range habitat cover at stopover localities. Results obtained from comparisons of soil covers between points randomly selected and true stopover localities sites revealed, as expected, the species may not select for particular habitats at a meso-scale range, because the habitat (or habitats) required by the species can be found virtually everywhere on their migration route. However, those birds stopping over in places richer in cropland or mosaic habitats including both cropland and forest and with proportionally less closed forest stayed for longer than in areas with lower surfaces of cropland and mosaic and more closed forest. This suggests that areas rich in cropland or mosaic habitat were optimal.     

Migratory Disturbance Thresholds with Mule Deer and Energy Development

Fine-scale movement data has transformed our knowledge of ungulate migration ecology and now provides accurate, spatially explicit maps of migratory routes that can inform planning and management at local, state, and federal levels. Among the most challenging land use planning issues has been developing energy resources on public lands that overlap with important ungulate habitat, including the migratory routes of mule deer (Odocoileus hemionus). We generally know that less development is better for minimizing negative effects and maintaining habitat function, but we lack information on the amount of disturbance that animals can tolerate before reducing use of or abandoning migratory habitat. We used global positioning system data from 56 deer across 15 years to evaluate how surface disturbance from natural gas well pads and access roads in western Wyoming, USA, affected habitat selection of mule deer during migration and whether any disturbance threshold(s) existed beyond which use of migratory habitat declined. We used resource and step selection functions to examine disturbance thresholds at 3 different spatial scales. Overall, migratory use by mule deer declined as surface disturbance increased. Based on the weight of evidence from our 3 independent but complementary metrics, declines in migratory use related to surface disturbance were non-linear, where migratory use sharply declined when surface disturbance from energy development exceeded 3%. Disturbance thresholds may vary across regions, species, or migratory habitats (e.g., stopover sites). Such information can help with management and land use decisions related to mineral leasing and energy development that overlap with the migratory routes of ungulates. © 2020 The Wildlife Society.     

Habitat use and movement patterns of Northern Pintails during spring in northern Japan: the importance of agricultural lands

ABSTRACT From 2006 to 2009, we marked 198 Northern Pintails (Anas acuta) with satellite transmitters on their wintering areas in Japan to study their migration routes and habitat use in spring staging areas. We hypothesized that the distribution of pintails during spring staging was influenced by patterns of land use and expected that the most frequently used areas would have more agricultural habitat than lesser‐used areas. We obtained 3031 daily locations from 163 migrant pintails marked with satellite transmitters and identified 524 stopover sites. Based on a fixed kernel home range analysis of stopover utilization distribution (UD), core staging areas (areas within the 50% UD) were identified in northern Honshu and western Hokkaido, and were used by 71% of marked pintails. Core staging areas had a greater proportion of rice fields than peripheral (51–95% UD) and rarely used (outside the 95% UD) staging areas. Stopover sites also contained more rice fields and other agricultural land than were available at regional scales, indicating that pintails selected rice and other agricultural habitats at regional and local scales. Pintails remained at spring staging areas an average of 51 d. Prolonged staging in agricultural habitats of northern Japan was likely necessary for pintails to prepare for transoceanic migration to Arctic nesting areas in eastern Russia.     

Fall Migration and Habitat Use of American Woodcock in the Central United States

Abstract: Little is known about the migration ecology of the American woodcock (Scolopax minor). From 2001 to 2003, we began a 3-year study to document woodcock fall migration routes, rates, and habitat use from Minnesota, Wisconsin, and Michigan, USA. Some 586 radiomarked woodcock initiated migration. During 224 hours of aerial telemetry, we located 42 radiomarked woodcock in 6 states. Using locations of radiomarked birds, we speculated woodcock migration routes in the central United States. Stopover duration often exceeded 4 days, with some birds stopping longer than a week. Radiomarked birds were located in upland habitats more frequently than bottomland habitats, and used a higher proportion of mature forest than expected. A Geographic Information System was used to map potential woodcock habitat in the Central Region. Based on our results, we identified possible fall migration routes and priority areas for woodcock management in the Central Region. Our results should be used by land managers to prioritize future land acquisition and management of woodcock habitat.     

Effects of weather variation on waterfowl migration: Lessons from a continental‐scale generalizable avian movement and energetics model

We developed a continental energetics‐based model of daily mallard (Anas platyrhynchos) movement during the non‐breeding period (September to May) to predict year‐specific migration and overwinter occurrence. The model approximates movements and stopovers as functions of metabolism and weather, in terms of temperature and frozen precipitation (i.e., snow). The model is a Markov process operating at the population level and is parameterized through a review of literature. We applied the model to 62 years of daily weather data for the non‐breeding period. The average proportion of available habitat decreased as weather severity increased, with mortality decreasing as the proportion of available habitat increased. The most commonly used locations during the course of the non‐breeding period were generally consistent across years, with the most inter‐annual variation present in the overwintering area. Our model revealed that the distribution of mallards on the landscape changed more dramatically when the variation in daily available habitat was greater. The main routes for avian migration in North America were predicted by our simulations: the Atlantic, Mississippi, Central, and Pacific flyways. Our model predicted an average of 77.4% survivorship for the non‐breeding period across all years (range = 76.4%–78.4%), with lowest survivorship during autumn (90.5 ± 1.4%), intermediate survivorship in winter (91.8 ± 0.7%), and greatest survivorship in spring (93.6 ± 1.1%). We provide the parameters necessary for exploration within and among other taxa to leverage the generalizability of this migration model to a broader expanse of bird species, and across a range of climate change and land use/land cover change scenarios.     

Green‐up selection by red deer in heterogeneous,human‐dominated landscapes of Central Europe

The forage maturation hypothesis (FMH) assumes that herbivores cope with the trade‐off between digestibility and biomass in forage by selecting vegetation at intermediate growth. The green wave hypothesis (GWH) extends the FMH to suggest how spatiotemporal heterogeneity in plant quality shapes migratory movements of herbivores. Growing empirical support for these hypotheses mainly comes from studies in vast landscapes with large‐scale habitat heterogeneity. It is unclear, however, to what extent ungulates surf green waves in human‐altered landscapes with small‐scale heterogeneity in terms of land use and topography. We used plant phenological proxies derived from Sentinel 2 satellite data to analyze the habitat selection of 93 collared red deer (Cervus elaphus) in montane and alpine habitats. Using a step selection analysis, we investigated how plant phenology, that is, the instantaneous rate of green‐up (IRG) and normalized difference vegetation index (NDVI), and a set of variables describing topography and human presence influenced red deer resource selection in open habitats. We learned that red deer selected areas with high biomass at green‐up and avoided habitats with possible exposure to human activity. Additionally, landscape structure and topography strongly influenced spatial behavior of red deer. We further compared cumulative access to high‐quality forage across migrant strategies and found migrants gained better access than residents. Many migratory individuals surfed the green wave, and their surfing behavior, however, became less pronounced with decreasing distance to settlements. Within the constraints of topography and human land use, red deer track spring green‐up on a fine spatiotemporal scale and follow the green wave across landscapes in migration movements. Thus, they benefit from high‐quality forage even in human‐dominated landscapes with small‐scale heterogeneity and vegetation emerging in a heterogenic, dynamic mosaic.     

鸿雁迁徙对停歇地的选择特征

建立合理的湿地水鸟保护地是缓解水鸟栖息地丧失和种群下降的重要手段。以往的保护地设计中,由于越冬地和和繁殖地水鸟停留时间长、种群数量大,受到较多的关注。分析湿地水鸟对停歇地的选择偏好,掌握停歇地的自然条件和人类活动特征可为水鸟保护网络优化和保护地管理提供决策依据。而在水鸟迁徙过程中,停歇地作为保护网络的重要节点也发挥了重要作用。因此选择鸿雁为伞护种,获取了29只鸿雁项圈追踪数据,分析蒙古国Khukh湖-中国东北鸭绿江口秋季迁徙路线对停歇地生境选择偏好,识别了鸿雁在湿地周边不同距离梯度下的活动频率变化。根据鸿雁停歇数据共识别停歇地63处,以此为基础分析停歇的自然条件和人类活动因素特征。结果表明,鸿雁除选择湖泊和沼泽为停歇地外,周边250m内的裸地和草地也是重要栖息地;当鸿雁停歇地人类活动较少时,鸿雁倾向于选择土壤肥沃、食物丰富区,而人类活动强度加大时,栖息地植被条件提高能够为鸿雁提供遮避条件,也吸引了更多鸿雁停歇。研究建议,在水鸟迁徙重要廊道区应增加水鸟停歇地保护区,保护区的设计应根据关键保护对象活动频率加强对湿地周边的栖息地保护,减少水滨人类活动对鸿雁停歇的负面影响;在人类活动强度较大的地区设立水鸟保护地,还应加强对植被的保护,在水鸟利用频率较高的停歇地周边进行植被修复。     

Vascular plant and ground beetle diversity on wet arable land versus conventional crop fields

While artificial farmland drainage has allowed the development of a highly productive agriculture, the availability of periodically flooded arable land as a niche habitat for a broad range of animal and vascular plant species has diminished. Accordingly, many species depending on temporary wetlands are endangered, already extinct or extirpated in Switzerland and other European countries. Some arable fields with temporary pools can still be observed in Switzerland. However, it is not known how suitable such small temporary ponds are as habitats in the modern, intensively-managed agricultural landscape, where disturbance rates are high, and connecting wetland habitats are scarce. We surveyed 120 fields across 10 hot spot regions for potential waterlogging in Switzerland, investigating the effect of temporary waterlogging on the diversity of arable plant and ground beetle species. Half of the fields were heavily influenced by waterlogging, while the other half represented conventional crop field controls. We found that wet fields exhibited a higher number of vascular plant and carabid species on average compared to control fields. This difference was explained by the presence of more hygrophilic plant and ground beetle species on wet fields. While we did find more hygrophilic species on wet fields, the threatened character species of temporary wetland habitats were mostly absent despite availability in regional species pools. These results suggest that temporary pools still provide the raw environmental characteristics that hygrophilic species require in the agricultural landscape. However, alternative management schemes are required to transform them into habitats that can effectively support high-priority, threatened species of temporary wetlands.     

Fishing cat Prionailurus viverrinus distribution and habitat suitability in Nepal

The fishing cat Prionailurus viverrinus is a wetland specialist species endemic to South and Southeast Asia. Nepal represents the northern limit of its biogeographic range, but comprehensive information on fishing cat distribution in Nepal is lacking. To assess their distribution, we compiled fishing cat occurrence records (n = 154) from Nepal, available in published literature and unpublished data (2009–2020). Bioclimatic and environmental variables associated with their occurrence were used to predict the fishing cat habitat suitability using MaxEnt modeling. Fishing cat habitat suitability was associated with elevation (152–302 m), precipitation of the warmest quarter, i.e., April–June (668–1014 mm), precipitation of the driest month (4–7 mm), and land cover (forest/grassland and wetland). The model predicted an area of 4.4% (6679 km²) of Nepal as potential habitat for the fishing cat. About two‐thirds of the predicted potentially suitable habitat lies outside protected areas; however, a large part of the highly suitable habitat (67%) falls within protected areas. The predicted habitat suitability map serves as a reference for future investigation into fishing cat distribution as well as formulating and implementing effective conservation programs in Nepal. Fishing cat conservation initiatives should include habitats inside and outside the protected areas to ensure long‐term survival. We recommend conservation of wetland sites, surveys of fishing cats in the identified potential habitats, and studying their genetic connectivity and population status.     

Community Structure of Wetland Birds During Spring Migration Through the Rainwater Basin

Abstract: Staging areas and migratory stopovers of wetland birds have the potential to function as geographic bottlenecks; entire populations within a flyway may be affected by the quality and quantity of available wetland habitat at stopover sites. Although approximately 90% of playa wetlands in the Rainwater Basin (RWB) region of south-central Nebraska, USA, have been destroyed, the area still provides essential stopover habitat for >10 million waterfowl each spring. We evaluated community patterns and species associations to assess importance of assembly rules in structuring wetland bird communities during migration and to better facilitate multispecies conservation and management strategies. We surveyed 36–40 playas twice weekly in the RWB and observed approximately 2.6 million individual migratory wetland birds representing 72 species during 3 spring migrations 2002–2004. We evaluated spatial and temporal species co-occurrence patterns of geese, dabbling ducks, diving ducks, and shorebirds using null model analysis. Goose species co-occurrence scores did not differ from random in any year of the study, suggesting that goose species frequently use the same habitats during migration. Co-occurrence patterns among dabbling ducks were not different than expected by chance in any year; however, when we evaluated co-occurrence at a weekly scale, dabbling ducks co-occurred less often than expected during weeks of peak migration (high abundance), indicating that dabbling duck species spatially segregated at high densities. Diving duck co-occurrence patterns did not differ from random in any year, suggesting that diving duck species used the same habitats during migration. Shorebird species co-occurred less often than expected in 2002 and 2004, and during weeks of high shorebird abundance, indicating that shorebird communities were distinctly structured during those times. Most association values among lesser snow geese (Chen caerulescens) and dabbling duck species were positive, indicating dabbling ducks did not avoid wetlands with snow geese, a concern for waterfowl managers. However, we frequently observed snow geese and dabbling ducks using different microhabitats within a wetland, which indicate species associations and co-occurrence patterns may have occurred at a finer spatial scale than we measured. This approach of co-occurrence analysis will allow wildlife managers charged with multispecies management at migration stopover sites to make informed conservation and management decisions based on community structure rather than historic single-species approaches.     

Mining citizen science data to explore stopover sites and spatiotemporal variation in migration patterns of the red-footed falcon

Citizen science data have already been used to effectively address questions regarding migration, a fundamental stage in the life history of birds. In this study, we use data from eBird and from 3 additional regional citizen science databases to describe the migration routes and timing of the red-footed falcon Falco vespertinus in the Mediterranean region across 8 years (2010–2017). We further examine the seasonal and yearly variation in migration patterns and explore sites used during the species migration. Our results suggest that the autumn passage is spatially less variable and temporally more consistent among years than in spring and that birds migrate faster in spring than in autumn. The species seems to be more prevalent along the Central Mediterranean during spring migration, probably as a result of the clockwise loop migration that red-footed falcons perform. There was a high variation in annual median migration dates for both seasons as well as in migration routes across years and seasons. Higher variation was exhibited in the longitudinal component thus indicating flexibility in migration routes. In addition, our results showed the species’ preference for lowlands covered with cropland and mosaics of cropland and natural vegetation as stopover sites during migration. Stopover areas predicted from our distribution modeling highlight the importance of the Mediterranean islands as stopover sites for sea-crossing raptors, such as the red-footed falcon. This study is the first to provide a broad-scale spatiotemporal perspective on the species migration across seasons, years and flyways and demonstrates how citizen science data can inform future monitoring and conservation strategies.     

Resident and transient coyotes exhibit differential patterns of movement behavior across heterogeneous landscapes in the southeastern United States

Coyotes (Canis latrans) are a highly adaptable canid species whose behavioral plasticity has allowed them to persist in a wide array of habitats throughout North America. As generalists, coyotes can alter movement patterns and change territorial strategies between residency (high site fidelity) and transiency (low site fidelity) to maximize fitness. Uncertainty remains about resident and transient coyote movement patterns and habitat use because research has reached conflicting conclusions regarding patterns of habitat use by both groups. We quantified effects of habitat on resident and transient coyote movement behavior using first passage time (FPT) analysis, which assesses recursive movement along an individual''s movement path to delineate where they exhibit area‐restricted search (ARS) behaviors relative to habitat attributes. We quantified monthly movement rates for 171 coyotes (76 residents and 53 transients) and then used estimated FPT values in generalized linear mixed models to quantify monthly habitat use for resident and transient coyotes. Transients had greater movement rates than residents across all months except January. Resident FPT values were positively correlated with agricultural land cover during fall and winter, but negatively correlated with agriculture during spring. Resident FPT values were also negatively correlated with developed habitats during May–August, deciduous land cover during June–August, and wetlands during September–January except November. FPT values of transient coyotes were positively correlated with developed areas throughout much of the year and near wetlands during July–September. Transient FPT values were negatively correlated with agriculture during all months except June and July. High FPT values (ARS behavior) of residents and transients were generally correlated with greater densities of edge habitat. Although we observed high individual variation in space use, our study found substantive differences in habitat use between residents and transients, providing further evidence that complexity and plasticity of coyote habitat use is influenced by territorial strategy.     

A place to land: spatiotemporal drivers of stopover habitat use by migrating birds

Migrating birds require en route habitats to rest and refuel. Yet, habitat use has never been integrated with passage to understand the factors that determine where and when birds stopover during spring and autumn migration. Here, we introduce the stopover‐to‐passage ratio (SPR), the percentage of passage migrants that stop in an area, and use 8 years of data from 12 weather surveillance radars to estimate over 50% SPR during spring and autumn through the Gulf of Mexico and Atlantic coasts of the south‐eastern US, the most prominent corridor for North America’s migratory birds. During stopovers, birds concentrated close to the coast during spring and inland in forested landscapes during autumn, suggesting seasonal differences in habitat function and highlighting the vital role of stopover habitats in sustaining migratory communities. Beyond advancing understanding of migration ecology, SPR will facilitate conservation through identification of sites that are disproportionally selected for stopover by migrating birds.     

Stopover duration,movement patterns and temporary home ranges of fall migrant yellow‐rumped warblers Setophaga coronata in native and anthropogenic woodlands of the Northern Prairie region,USA

Stopover behavior of migrant birds is influenced by their energetic condition, but also by extrinsic factors, including weather conditions and habitat attributes such as vegetation structure, microclimates, predation pressure, competition, and food availability. Anthropogenic habitats may differ from natural habitats in these attributes, which could promote differing stopover behaviors for migrants in the two habitat types and affect overall habitat suitability. We used radio‐telemetry to measure stopover behaviors of fall migrant yellow‐rumped warblers Setophaga coronata in native riparian corridor woodlands (corridors) and anthropogenic woodlots (woodlots) in the Northern Prairie region. We measured stopover duration, movement rate, and temporary home range size for birds in both habitat types by attaching radio‐transmitters and relocating birds to either corridor (n = 17) or woodlot (n = 16) study sites. We used AIC_C to rank null, global, and reduced models, which included habitat type, energetic condition, habitat size, year, date, and movement rate (for stopover duration analyses only) as explanatory variables. Model rankings showed that habitat type was not included in any of the top models (ΔAIC_C < 2) for movement behavior, temporary home range size, or stopover duration, which suggests similar functional habitat quality between the two habitat types. These data add similar behavioral responses for birds in the two habitat types to similar fattening rates and stress physiology, further confirming similar suitability of native and anthropogenic woodland habitats in this region as stopover habitat. We also applied logistic regression with a model selection approach, including cloud cover, tail wind component, temperature, and barometric pressure as independent variables, and departure decision as the dependent variable, to evaluate the effects of weather variables on departure. Model selection suggested that cloud cover is a prominent factor affecting departure decisions and the other variables may also influence departure decisions of yellow‐rumped warblers from inland stopover sites.     

Biofilm Consumption and Variable Diet Composition of Western Sandpipers (Calidris mauri) during Migratory Stopover

Many shorebird species undertake long-distance migrations punctuated by brief stays at food-rich, estuarine stopover locations. Understanding use of these food resources helps guide conservation and responsible development decisions. We determined the extent and degree to which Western Sandpiper (Calidris mauri) utilized biofilm as a food resource across a large and variable stopover location during northward (spring) migration. We investigated the spatial heterogeneity in diet composition, to determine whether shorebirds were consistently feeding on biofilm or whether diet varied between naturally and anthropogenically delineated sites. We used stable isotope analysis to estimate that biofilm conservatively comprised 22% to 53% of Western Sandpiper droppings across all sampling sites and that prey composition differed significantly between areas within the stopover location. Widespread biofilm consumption demonstrates the importance of biofilm as a dietary component. Variable diet composition suggests that habitat heterogeneity may be an important component of high quality stopover locations in the context of “state-dependant trade-offs” of Western Sandpiper population sub-groups. Future management decisions must consider and address potential impacts on the biofilm community throughout a stopover location, as single site studies of diet composition may not be adequate to develop effective management strategies for entire stopover sites.     

Semi‐intensive shrimp farms as experimental arenas for the study of predation risk from falcons to shorebirds

Varying environmental conditions and energetic demands can affect habitat use by predators and their prey. Anthropogenic habitats provide an opportunity to document both predation events and foraging activity by prey and therefore enable an empirical evaluation of how prey cope with trade‐offs between starvation and predation risk in environments of variable foraging opportunities and predation danger. Here, we use seven years of observational data of peregrine falcons Falco peregrinus and shorebirds at a semi‐intensive shrimp farm to determine how starvation and predation risk vary for shorebirds under a predictable variation in foraging opportunities. Attack rate (mean 0.1 attacks/hr, equating 1 attack every ten hours) was positively associated with the total foraging area available for shorebirds at the shrimp farm throughout the harvesting period, with tidal amplitude at the adjacent mudflat having a strong nonlinear (quadratic) effect. Hunt success (mean 14%) was higher during low tides and declined as the target flocks became larger. Finally, individual shorebird vigilance behaviors were more frequent when birds foraged in smaller flocks at ponds with poorer conditions. Our results provide empirical evidence of a risk threshold modulated by tidal conditions at the adjacent wetlands, where shorebirds trade‐off risk and rewards to decide to avoid or forage at the shrimp farm (a potentially dangerous habitat) depending on their need to meet daily energy requirements. We propose that semi‐intensive shrimp farms serve as ideal “arenas” for studying predator–prey dynamics of shorebirds and falcons, because harvest operations and regular tidal cycles create a mosaic of foraging patches with predictable food supply. In addition, the relatively low hunt success suggests that indirect effects associated with enhanced starvation risk are important in shorebird life‐history decisions.