Explore the vast range of titles available.

Defining and identifying changes to seasonal ranges of migratory species is required for effective conservation. Historic sightings of migrating whooping cranes (Grus americana) have served as sole source of information to define a migration corridor in the Great Plains of North America (i.e., Canadian Prairies and United States Great Plains) for this endangered species. We updated this effort using past opportunistic sightings from 1942-2016 (n = 5,055) and more recent (2010-2016) location data from 58 telemetered birds (n = 4,423) to delineate migration corridors that included 50%, 75%, and 95% core areas. All migration corridors were well defined and relatively compact, with the 95% core corridor averaging 294 km wide, although it varied approximately ±40% in width from 170 km in central Texas to 407 km at the international border of the United States and Canada. Based on historic sightings and telemetry locations, we detected easterly movements in locations over time, primarily due to locations west of the median shifting east. This shift occurred from northern Oklahoma to central Saskatchewan at an average rate of 1.2 km/year (0.3-2.8 km/year). Associated with this directional shift was a decrease in distance of locations from the median in the same region averaging -0.7 km/year (-0.3--1.3 km/year), suggesting a modest narrowing of the migration corridor. Changes in the corridor over the past 8 decades suggest that agencies and organizations interested in recovery of this species may need to modify where conservation and recovery actions occur. Whooping cranes showed apparent plasticity in their migratory behavior, which likely has been necessary for persistence of a wetland-dependent species migrating through the drought-prone Great Plains. Behavioral flexibility will be useful for whooping cranes to continue recovery in a future of uncertain climate and land use changes throughout their annual range.

Species–area relationships are the product of many ecological processes and their interactions. Explanations for the species–area relationship (SAR) have focused on separating putative niche-based mechanisms that correlate with area from sampling effects caused by patches with more individuals containing more species than patches with fewer individuals. We tested the hypothesis that SARs in breeding waterfowl communities are caused by sampling effects (i.e. random placement from the regional species pool). First, we described observed SARs and patterns of species associations for fourteen species of ducks on ponds in prairie Canada. Second, we used null models, which randomly allocated ducks to ponds, to test if observed SARs and patterns of species associations differed from those expected by chance. Consistent with the sampling effects hypothesis, observed SARs were accurately predicted by null models in three different years and for diving and dabbling duck guilds. This is the first demonstration that null models can predict SARs in waterbirds or any other aquatic organisms. Observed patterns of species association, however, were not well predicted by null models as in all years there was less observed segregation among species (i.e. more aggregation) than under the random expectation, suggesting that intraspecific competition could play a role in structuring duck communities. Taken together, our results indicate that when emergent properties of ecological communities such as the SAR appear to be caused by random processes, analyses of species associations can be critical in revealing the importance of niche-based processes (e.g. competition) in structuring ecological communities.

Wildlife species confront threats from climate and land use change, exacerbating the influence of extreme climatic events on populations and biodiversity. Migratory waterbirds are especially vulnerable to hydrological drought via reduced availability of surface water habitats. We assessed how whooping cranes (Grus americana) modified habitat use and migration strategies during drought to evaluate their resilience to changing conditions and adaptive capacity. We categorized >8000 night‐roost sites used by 146 cranes from 2010 to 2022 and examined relative use during non‐drought, moderate drought, and extreme drought conditions. We found cultivated and uncultivated palustrine and lacustrine wetlands were generally used less during droughts than non‐drought conditions. Conversely, impounded palustrine and lacustrine systems and rivers served more frequently as drought refugia (i.e., used more during drought than non‐drought conditions). Night roosts occurred primarily on private lands (86% overall); public land use decreased with latitude and increased with drought severity, with greatest use (56%) occurring during severe autumn drought in the southern Great Plains. Quantifying use of identified critical habitats in the United States indicated that Cheyenne Bottoms State Waterfowl Management Area and Quivira National Wildlife Refuge were used less during drought, and the Central Platte River and Salt Plains National Wildlife Refuge received similar use during drought compared to non‐drought conditions. Our findings provide insights into compensatory use of habitats, where impounded surface water may function in a complementary fashion with natural wetlands. Collectively, these and other types of wetlands distributed across the migration corridor provided a reliable network of habitat available across the Great Plains. A diversity of wetlands available during variable environmental conditions would be useful in supporting continued recovery of whooping cranes and likely have benefits for a wide array of migratory birds. Wildlife, particularly migratory waterbirds like whooping cranes, face increasing threats from climate change and land use shifts, especially during extreme weather events. Whooping cranes readily modified habitat use more so than migration patterns when encountering drought conditions. Regional patterns in habitat use shifts were evident but, overall, cultivated wetlands were used less and impounded wetlands and lakes used more during drought compared to non‐drought conditions. These findings underscore the importance of diverse wetland habitats in the Great Plains for supporting the recovery of whooping cranes and other migratory birds.

Electricity generation from renewable-energy sources has increased dramatically worldwide in recent decades. Risks associated with wind-energy infrastructure are not well understood for endangered Whooping Cranes (Grus americana) or other vulnerable Crane populations. From 2010 to 2016, we monitored 57 Whooping Cranes with remote-telemetry devices in the United States Great Plains to determine potential changes in migration distribution (i.e., avoidance) caused by presence of wind-energy infrastructure. During our study, the number of wind towers tripled in the Whooping Crane migration corridor and quadrupled in the corridor’s center. Median distance of Whooping Crane locations from nearest wind tower was 52.1 km, and 99% of locations were >4.3 km from wind towers. A habitat selection analysis revealed that Whooping Cranes used areas ≤5.0 km (95% confidence interval [CI] 4.8–5.4) from towers less than expected (i.e., zone of influence) and that Whooping Cranes were 20 times (95% CI 14–64) more likely to use areas outside compared to adjacent to towers. Eighty percent of Whooping Crane locations and 20% of wind towers were located in areas with the highest relative probability of Whooping Crane use based on our model, which comprised 20% of the study area. Whooping Cranes selected for these places, whereas developers constructed wind infrastructure at random relative to desirable Whooping Crane habitat. As of early 2020, 4.6% of the study area and 5.0% of the highest-selected Whooping Crane habitat were within the collective zone of influence. The affected area equates to habitat loss ascribed to wind-energy infrastructure; losses from other disturbances have not been quantified. Continued growth of the Whooping Crane population during this period of wind infrastructure construction suggests no immediate population-level consequences. Chronic or lag effects of habitat loss are unknown but possible for long-lived species. Preferentially constructing future wind infrastructure outside of the migration corridor or inside of the corridor at sites with low probability of Whooping Crane use would allow for continued wind-energy development in the Great Plains with minimal additional risk to highly selected habitat that supports recovery of this endangered species.

The Aransas-Wood Buffalo population (the only non-reintroduced, migratory population) of endangered whooping cranes (Grus americana) overwinters along the Texas Gulf Coast, USA. Understanding whooping crane space use on the wintering grounds reveals essential aspects of this species' ecology, which subsequently assists with conservation. Using global positioning system telemetry data from marked whooping cranes during 2009–2017, we fit continuous-time stochastic process models to describe movement and home range using autocorrelated kernel density estimation (AKDE) and explored variation in home range size in relation to age, sex, reproductive status, and drought conditions. We used the Bhattacharyya coefficient of overlap and distance between home range centroids to quantify site fidelity. We examined the effects of time between winter home ranges and the sex of the crane on site fidelity using Bayesian mixed-effects beta regression. Winter whooping crane 95% AKDE home range size averaged 30.1 ± 45.2 (SD) km² (median = 14.3, range = 1.1–308.6). Home ranges of sub-adult females were approximately 2 times larger than those of sub-adult males or families. As drought worsened, home ranges typically expanded. Between consecutive years, the home ranges of an adult crane exhibited 68 ± 31% overlap (site fidelity), but fidelity to winter sites declined in subsequent winters. The overlap of adult home ranges with the nearest unrelated family averaged 33 ± 28%. As a whooping crane aged, overlap with its winter home range as a juvenile declined, regardless of sex. By 4 years of age, a whooping crane had approximately 14 ± 28% overlap with its juvenile winter home range. Limited evidence suggested male whooping cranes return to within 2 km of their juvenile home range by their fifth winter. Previous data obtained from aerial surveys led ecologists to assume that whooping crane families normally used small areas (~2 km²) and expressed persistent site fidelity. Our analyses showed <8% of families had home ranges ≤2 km², with the average area 15 times greater, and waning site fidelity over time. Our work represents an analysis of whooping crane home ranges for this population, identifying past misconceptions of winter space use and resulting in better estimates of space requirements for future conservation efforts.

Migratory birds use numerous strategies to successfully complete twice-annual movements between breeding and wintering sites. Context for conservation and management can be provided by characterizing these strategies. Variations in strategy among and within individuals support population persistence in response to changes in land use and climate. We used location data from 58 marked Whooping Cranes (Grus americana) from 2010 to 2016 to characterize migration strategies in the U.S. Great Plains and Canadian Prairies and southern boreal region, and to explore sources of heterogeneity in their migration strategy, including space use, timing, and performance. Whooping Cranes completed ∼3,900-km migrations that averaged 29 days during spring and 45 days during autumn, while making 11–12 nighttime stops. At the scale of our analysis, individual Whooping Cranes showed little consistency in stopover sites used among migration seasons (i.e. low site fidelity). In contrast, individuals expressed a measure of consistency in timing, especially migration initiation dates. Whooping Cranes migrated at different times based on age and reproductive status, where adults with young initiated autumn migration after other birds, and adults with and without young initiated spring migration before subadult birds. Time spent at stopover sites was positively associated with migration bout length and negatively associated with time spent at previous stopover sites, indicating Whooping Cranes acquired energy resources at some stopover sites that they used to fuel migration. Whooping Cranes were faithful to a defined migration corridor but showed less fidelity in their selection of nighttime stopover sites; hence, spatial targeting of conservation actions may be better informed by associations with landscape and habitat features rather than documented past use at specific locations. The preservation of variation in migration strategies existing within this species that experienced a severe population bottleneck suggests that Whooping Cranes have maintained a capacity to adjust strategies when confronted with future changes in land use and climate.

Much previous research has focussed on the role of food supply in determining the growth and the survival of avian offspring. More recently, acid deposition in some ecosystems has demonstrated that in addition to energy, birds also need to acquire sufficient nutrients such as calcium to be successful. Whether procurement of adequate levels of calcium can limit reproductive success in areas that have not been impacted by acid rain remains equivocal. We tested whether calcium affected reproductive success of tree swallows Tachycineta bicolor by feeding extra calcium to nestlings during the brood-rearing period. Our manipulation did not enhance the survival of offspring, however, provisioning of extra calcium resulted in nestlings showing enhanced rates of growth of mass (all nests) and of ninth primary flight feathers (nests with after-second year female parents), compared to control nestlings. Calcium supplementation also resulted in nestlings having longer feathers and tarsi at age 16 days, and there was evidence that some nestlings receiving extra calcium were heavier at 16 days old. As offspring that have faster growth, or that are in good condition at fledging, often survive better after leaving the nest, these results suggest that calcium availability can limit fitness. Our results are noteworthy because our experiment was conducted in an area with abundant soil calcium where acid deposition has not occurred. The role of calcium in limiting the reproductive performance of avian species may therefore be more pervasive than previously thought.

Waterbird species face numerous threats and many are declining globally, but knowledge of distribution, abundance, and trend remains poor for many species. Five species of marsh-nesting colonial waterbirds are poorly monitored in Canada, and especially so in the core of their range in the Canadian Prairie Provinces (Alberta, Saskatchewan, and Manitoba). We summarized published and unpublished data on abundance and distribution of breeding colonies of Western Grebe (Aechmophorus occidentalis), Franklin's Gull (Leucophaeus pipixcan), Black Tern (Chlidonias niger), Forster's Tern (Sterna forsteri), and Black-crowned Night-Heron (Nycticorax nycticorax) in Alberta, Saskatchewan, and Manitoba. We also examined the degree of overlap in nesting phenology (egg dates) and summarized survey methods that have been used to monitor the species during the breeding season—information that may be useful for the development of a multispecies monitoring program. For all species, the largest number of records of breeding colonies occurred in Alberta, with records declining eastward through Saskatchewan and Manitoba. We identified a number of breeding colonies occurring outside of currently defined species ranges, especially for the poorly studied Forster's Tern. Of 137 waterbodies hosting a colony of at least one species over the past 10 yr, 57 (41.6%) hosted colonies of at least 2 species, and 3 (2.2%) hosted colonies of all 5 species. Species tended to be reasonably synchronous in their breeding phenology, but Franklin's Gulls and Black-crowned Night-Herons tended to initiate nesting slightly earlier than the other species. We conclude that a multispecies survey timed in late May or early June to count nests and/or incubating adults, using either ground-based or aerial surveys, would likely be the most appropriate for monitoring all species jointly in the Prairie Provinces. The approach we take to compiling data from multiple sources on species occurrence and breeding phenology may be applicable to others wishing to examine the feasibility of a multispecies monitoring plan.

Understanding how animals respond to changing habitat conditions can improve predictions about effects of environmental change and also inform conservation planning. We examined relationships between abundances of 5 common dabbling duck species breeding in the Canadian Prairie Pothole Region and basic wetland metrics. Pond area was a well-supported predictor of duck abundance at the local scale of pond. Relationships for all 5 species varied with their respective regional duck and pond densities. In regions where duck densities were high, there were more ducks per pond; conversely, there were fewer ducks per pond in regions where pond densities were high, indicating that mechanisms influencing local habitat use were, in part, mediated by processes occurring at larger spatial scales. Although models explained small amounts of variation of duck abundance on a per pond basis, these models explained more variation when results were aggregated to the level of survey segment, indicating reasonable performance of models for estimating duck abundance over specific areas with known pond areas. Our results also indicated that the greatest increase in duck abundance with increasing pond size occurs at the low end of the range of pond sizes. It is relatively small wetlands that face the greatest threat of loss and degradation on the prairies; therefore, protection and conservation efforts need to focus on these wetlands if the objective is to increase or maintain populations of the duck species studied.

Waterbird species face numerous threats and many are declining globally, but knowledge of distribution, abundance, and trend remains poor for many species. Five species of marsh-nesting colonial waterbirds are poorly monitored in Canada, and especially so in the core of their range in the Canadian Prairie Provinces (Alberta, Saskatchewan, and Manitoba). We summarized published and unpublished data on abundance and distribution of breeding colonies of Western Grebe (Aechmophorus occidentalis), Franklin's Gull (Leucophaeus pipixcan). Black Tern (Chlidonias niger), Forster's Tern (Sterna forsteri), and Black-crowned Night-Heron (Nycticorax nycticorax) in Alberta. Saskatchewan, and Manitoba. We also examined the degree of overlap in nesting phenology (egg dates) and summarized survey methods that have been used to monitor the species during the breeding season--information that may be useful for the development of a multispecies monitoring program. For all species, the largest number of records of breeding colonies occurred in Alberta, with records declining eastward through Saskatchewan and Manitoba. We identified a number of breeding colonies occurring outside of currently defined species ranges, especially for the poorly studied Forster's Tern. Of 137 waterbodies hosting a colony of at least one species over the past 10 yr, 57 (41.6%) hosted colonies of at least 2 species, and 3 (2.2%) hosted colonies of all 5 species. Species tended to be reasonably synchronous in their breeding phenology, but Franklin's Gulls and Black-crowned Night-Herons tended to initiate nesting slightly earlier than the other species. We conclude that a multispecies survey timed in late May or early June to count nests and/or incubating adults, using either ground-based or aerial surveys, would likely be the most appropriate for monitoring all species jointly in the Prairie Provinces. The approach we take to compiling data from multiple sources on species occurrence and breeding phenology may be applicable to others wishing to examine the feasibility of a multispecies monitoring plan. Received 19 December 2018. Accepted 2 April 2019.