Understanding the Winter Ecology of Sandhill Cranes

Photo by Larry Kruckenberg

Understanding the role of habitat use, seasonal movement, and mortality to describe the winter ecology of the Rocky Mountain Population of Sandhill Cranes (Grus canadensis) in the middle Rio Grande Valley of New Mexico

The Rocky Mountain Population (RMP) of greater sandhill cranes (Grus canadensis tabida) recovered from low numbers in the early 1900s (≈ 150-200) to >21,000 cranes by 2008 (Kruse et al. 2009). Fall population estimates indicate that the size of the RMP has been relatively stable since 1995 (Sharpe et al. 2002), but recently there is concern that habitat fragmentation, changes in agricultural practices, low recruitment, and harvest pressure (Drewien personal communication) have had an impact on the RMP (Drewien et al 1995, McWethy and Austin 2009).  Additionally, population indices from the last three years (Kruse et al. 2013) indicate a population decline; even though current population numbers are within the population goals set by the RMP Cooperative Flyway Management Plan (17,000 – 21,000; Pacific and Central Flyway Councils 2007).   This decline is most concerning because if landscape level changes or managed harvest rates are negatively affecting the population, corrective management actions, after the fact, can result in very slow recovery. 

The Middle Rio Grande Valley (MRGV) is the principal wintering area for RMP sandhill cranes in New Mexico, mainly from Albuquerque south to Bosque del Apache National Wildlife Refuge (BdA) at San Antonio, NM. The valley has long been recognized as an important wintering area for cranes (Pacific and Central Flyway Councils 2007) and is the site of the annual Crane Festival that draws tens of thousands of visitors to marvel at the flights of sandhill cranes moving between roosts and foraging sites. Most cranes winter on BdA or on the New Mexico Department of Game and Fish’s property, Bernardo Wildlife Area. These two areas alone are the single most important wintering areas for RMP cranes in the MRGV (Drewien and Bizeau 1974).

Throughout their winter range agricultural practices are changing, acreage of corn and small grains are decreasing due to increased demand for water, and water availability due to persistent drought is decreasing. Therefore, it is crucial that we identify the limiting factors driving seasonal movement patterns, habitat use, resource selection, and mortality of RMP cranes.  It would be most beneficial to study RMP cranes across their seasonal distributions simultaneously.  However, to accomplish this would be quite difficult from logistical and financial perspectives.  The optimal approach for identifying factors limiting population growth, and contributing to current population declines, is to start where the birds are concentrated, the wintering grounds.  Wintering areas may represent the greatest potential impacts to crane population dynamics as a result of changing land-use practices and high rates of cause-specific mortality.  Cranes can also be most efficiently captured on wintering sites, and data collected from marked cranes have potential to inform breeding season studies.  Over the next four years, we will work towards completing previously stated objectives to inform conservation and management decisions and provide a foundation  for continued studies on the breeding grounds in Colorado, Idaho, Montana, Utah, and Wyoming where our research efforts can be focused using data collected from GPS collars.

Primary Objectives:

1.      Estimate over winter survival and non-hunting mortality of RMP Sandhill Cranes in the MRGV

2.      Determine seasonal habitat use and resource selection using VHF radio and GPS satellite transmitters

3.      Use VHF and GPS locations to understand spatially explicit winter movement patterns of RMP Sandhill Cranes in the MRGV

4.      Link winter movements to managed habitats on private and public land to understand role of RMP Sandhill Cranes in crop depredation

5.      Use movement, habitat use, and resource selection to build a bioenergetics model for RMP Sandhill Cranes in the MRGV

6.      Estimate carrying capacity from habitat use, habitat availability, winter movements, and bioenergetics model

Secondary Objectives:

1.    Delineate and identify use areas outside of traditional known breeding areas

2.    Assess habitat selection, use, and condition on the breeding grounds

3.    Develop foundation of seasonal movement to inform breeding season studies using GPS transmitters

Primary Investigators:

  • Dan Collins, Regional Migratory Game Bird Coordinator, U.S. Fish and Wildlife Service,  Region 2, Migratory Bird Office
  • Scott Carleton, Assistant Unit Leader, U.S. Geological Survey, New Mexico Cooperative Fish and Wildlife Research Unit, New Mexico State University
  • John Vradenburg, Land Management and Research Demonstration Biologist
  • Managed Arid Wetlands and Riparian Areas, Bosque del Apache NWR
  • Ashley Inslee, Bosque del Apache National Wildlife Refuge