ABSTRACT
Annual phenology and distributions of migratory wildlife have been noticeably influenced by climate change, leading to concerns about sustainable populations. Recent studies exploring conditions influencing autumn migration departure have provided conflicting insights regarding factors influencing the movements of Mallards (Anas platyrhynchos), a popular game species. We determined factors affecting timing and magnitude of long-distance movements of 97 juvenile Mallards during autumn-winter across the midcontinent of North America marked with implanted transmitters in North and South Dakota, 2018-2019. Factors influencing variation in movement timing, along with direction and magnitudes, depended on type of movement (i.e., regional [25-310 km], initial migration, or subsequent migration movements [>310 km]). Photoperiod influenced probability of initiating all movements, although the effect was most influential for regional movements. Minimum temperature most influenced initial migration events (probability of movement increased 29% for each 1°C decrease); favorable winds also increased likelihood of initial migration events. Probability of subsequent migration events increased 80% for each 1 cm increase in depth of snow. Subsequent migration movements also were 2.0 times more likely to occur on weekend days, indicating disturbance from humans may influence movements. Migration distances increased 166 km for each 1°C reduction in minimum temperature. We also observed markedly different autumn-winter distributions of marked birds between years. Median locations during autumn-winter 2018-2019 were ~250 km farther north and ~300 km farther west during mid-December-January compared to the same time in 2019-2020. Concurrently, harvest rates for marked females and males were 10% and 26% during autumn-winter 2018-2019 and 26% and 31% during autumn-winter 2019-2020. Climate-related changes may result in increasingly variable autumn-winter distributions, with implications for wildlife recreationalists, conservation planners, and harvest managers.
ABSTRACT
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.
Subject(s)
Birds , Wind , Animals , Ecosystem , Endangered SpeciesABSTRACT
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.
Subject(s)
Animal Migration , Birds/physiology , Animals , Canada , Endangered Species , Oklahoma , Saskatchewan , TexasABSTRACT
Previous studies of migratory sandhill cranes (Grus canadensis) have made significant progress explaining evolution of this group at the species scale, but have been unsuccessful in explaining the geographically partitioned variation in morphology seen on the population scale. The objectives of this study were to assess the population structure and gene flow patterns among migratory sandhill cranes using microsatellite DNA genotypes and mitochondrial DNA haplotypes of a large sample of individuals across three populations. In particular, we were interested in evaluating the roles of Pleistocene glaciation events and postglaciation gene flow in shaping the present-day population structure. Our results indicate substantial gene flow across regions of the Midcontinental population that are geographically adjacent, suggesting that gene flow for most of the region follows an isolation-by-distance model. Male-mediated gene flow and strong female philopatry may explain the differing patterns of nuclear and mitochondrial variation. Taken in context with precise geographical information on breeding locations, the morphologic and microsatellite DNA variation shows a gradation from the Arctic-nesting subspecies G. c. canadensis to the nonArctic subspecies G. c. tabida. Analogous to other Arctic-nesting birds, it is probable that the population structure seen in Midcontinental sandhill cranes reflects the result of postglacial secondary contact. Our data suggest that subspecies of migratory sandhills experience significant gene flow and therefore do not represent distinct and independent genetic entities.
