River ecosystems in semi-arid environments provide an array of resources that concentrate biodiversity, but also attract human settlement and support economic development. In the southwestern United States, land-use change, drought, and anthropogenic disturbance are compounding factors which have led to departures from historical conditions of river ecosystems, consequently affecting wildlife habitat, including important wintering areas for migratory birds. The Rio Grande (River) in central New Mexico is the lifeblood of the Middle Rio Grande Valley (MRGV), maintaining large urban and agricultural centers and riparian and wetland resources, which disproportionately support a diversity of wildlife. The MRGV has been identified as the most important wintering area for the Rocky Mountain Population of greater sandhill cranes (Antigone canadensis tabida). Presently, however, changes in the hydrogeomorphology of the Rio Grande and landscape modification by humans have reshaped the MRGV and winter habitat for sandhill cranes. To evaluate these impacts, we investigated how land-use practices, anthropogenic disturbance, and river morphology influenced patterns of diurnal and roosting habitat selection by sandhill cranes. During the diurnal period, sandhill cranes relied heavily on managed public lands selecting agriculture crops, such as corn fields, and wetlands for foraging and loafing while avoiding areas with increasing densities of human structures. Sandhill cranes selected areas for roosting in the Rio Grande characterized by shallower water interspersed with sandbars, wide channel width, low bank vegetation, and farther away from disturbances associated with bridges. Our results establish and identify the central processes driving patterns of diel habitat selection by wintering sandhill cranes. Land use and riverine trends have likely gradually reduced winter habitat to managed public lands and limited reaches of the Rio Grande, underscoring the importance of natural resources agencies in supporting migratory birds and challenges involved when managing for wildlife in highly pressured semi-arid environments.

Population delineation throughout the annual life cycle for migratory birds is needed to formulate regional and national management and conservation strategies. Despite being well studied continentally, connectivity of sandhill crane Grus canadensis populations throughout the western portion of their North American range remains poorly described. Our objectives were to 1) use global positioning system satellite transmitter terminals to identify summer distributions for the Lower Colorado River Valley Population of greater sandhill cranes Grus canadensis tabida and 2) determine whether intermingling occurs among any of the western greater sandhill crane populations: Rocky Mountain Population, Lower Colorado River Valley Population, and Central Valley Population. Capture and marking occurred during winter and summer on private lands in California and Idaho as well as on two National Wildlife Refuges: Cibola and Sonny Bono Salton Sea National Wildlife Refuges. A majority of marked greater sandhill cranes summered in what is established Lower Colorado River Valley Population breeding areas in northeastern Nevada and southwestern Idaho. A handful of greater sandhill cranes summered outside of traditional breeding areas in west-central Idaho around Cascade Reservoir near Donnelly and Cascade, Idaho. For example, a greater sandhill crane colt captured near Donnelly in July 2014 survived to winter migration and moved south to areas associated with the Rocky Mountain Population. The integration of the greater sandhill crane colt captured near Donnelly provides the first evidence of potential intermingling between the Lower Colorado River Population and Rocky Mountain Population. We suggest continued marking and banding efforts of all three western populations of greater sandhill cranes will accurately delineate population boundaries and connectivity and inform management decisions for the three populations.

Citation: Boggie, M. A., S. A. Carleton, D. P. Collins, J. Vradenburg, and C. J. Sroka. 2018. Using stable isotopes to estimate reliance on agricultural food subsidies and migration timing for a migratory bird. Ecosphere 9(2):e02083.10. 1002/ecs2.2083 Abstract. Anthropogenic activities have adversely transformed terrestrial ecosystems consequently limiting many species to more fragmented areas and increasing human-wildlife conflicts. Under some circumstances, this creates a need for management programs to support wildlife populations by subsidizing food resources. Evaluation and improvement of supplementary feeding practices should be implemented to determine dietary importance of supplementary food and identify when to make food resources available, an important consideration for migratory species using seasonal habitats. Large aggregations of greater sandhill cranes (Antigone canadensis tabida) wintering in the Middle Rio Grande Valley of central New Mexico have come into conflict with agricultural practices. Resulting crop depredation on private lands has consequently required a mitigation program that subsidizes cranes with cultivated corn to manage their foraging behavior and provide nutritive support. To assess dependency of cranes on corn subsidies and estimate arrival dates of migratory sandhill cranes, we measured stable isotope ratios of liver and muscle tissues of sandhill cranes and their food items during winter. Over 60% of sandhill crane diet in the winter came from corn subsidies. Rates of carbon isotope incorporation in liver and muscle tissues were 0.03 d À1 AE 0.02 (mean AE SE) and 0.02 d À1 AE 0.01, respectively, and differed predictably by metabolic activity of different tissues. Estimated arrival date on wintering grounds derived from rates of carbon isotope incorporation was November 6 AE 3 d (mean AE SE) and was within 17 d of the estimated arrival date on the wintering grounds of sandhill cranes equipped with satellite transmitters (November 23 AE 2 d). Our approach demonstrates a field-based application of intrinsic biomarkers to inform supplementary feeding practices for wildlife populations by identifying dietary response to supplementary food. Additionally, estimating arrival on wintering grounds supports management and conservation decisions by synchronizing availability of supplementary food resources with arrival times.

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