USGS - science for a changing world

Northern Prairie Wildlife Research Center

  Home About NPWRC Our Science Staff Employment Contacts Common Questions About the Site

Grays Lake Ecosystem

Breeding Ecology of Sandhill Cranes at Grays Lake National Wildlife Refuge, Idaho

Joe Ball, Co-Project Leader and Adonia Henry, Research Assistant
Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, MT

Jane Austin, Co-Project Leader
USGS, Northern Prairie Research Center, SE, Jamestown, ND


Ball, I. J., J. E. Austin, and A. R. Henry.   2003.   Population and nesting 
     ecology of sandhill cranes at Grays Lake, Idaho, 1997-2000.  U.S. 
     Geological Survey, Montana Cooperative Wildlife Research Unit, Missoula, 
     MT and Northern Prairie Wildlife Research Center, Jamestown, ND.  Final 
     report to U.S. Fish and Wildlife Service February 2003.

Abstract:  We examined population and nesting ecology of greater sandhill cranes (Grus canadensis tabida) at Grays Lake National Wildlife Refuge (GLNWR) during 1997-2000. The primary objectives of our work were to 1) determine size, social components, and recruitment of crane populations at Grays Lake; 2) assess reliability and repeatability of census techniques; 3) evaluate factors affecting distribution and success of nests; and 4) evaluate the magnitude, and if possible the causes, of historic changes in breeding populations, fall staging populations, nest success, and recruitment of cranes at Grays Lake.

The average local population of cranes in late April-early May, 1998-2000, was 735 cranes, 34% higher than that reported for May 1970-1971 ( = 549; Drewien 1973) and 63% of the peak estimated population reported for mid-June 1979-1982 ( = 1,175; GLNWR Narrative Reports, 1979-1982). Pair numbers during mid to late April 1999-2000 ranged from 222 to 256 and were similar to indicated pair counts during 1970-1971. Current estimate of nests in the basin core (excluding renests) was 228 30, 16% higher than the 1971 estimate (Drewien 1973). Fall crane numbers peaked during 11-16 September 1998 ( = 1,210), 16-20 September 1999 ( = 1,530), and 5-8 September 2000 ( = 1,663). We estimated local recruitment from mid-August counts at 4.7% in 1998, 4.2% in 1999, and 2.3% in 2000. Estimated regional recruitment from September counts averaged 5.4% in 1998, 5.9% in 1999, and 1.4% in 2000. High recruitment during the 1980s, high adult survival, and a tendency to return to natal areas likely have helped maintain the local population through a period of low recruitment in the 1990s. Trends in fall populations at Grays Lake appear to be influenced by drought and changes in local and regional agricultural practices. Recruitment likely has been affected by drought and changes in predator communities.

We collected information on >500 nests. Peak nest initiation occurred during late April-mid May in all years. Clutch size averaged 1.89, with little variation among years. Crane nests were most abundant in semi-wet meadow, Baltic rush, and cattail/bulrush habitats. Most nests were located in water 10 cm deep, 40-50 m from shore, and in areas of low to moderate isolation by water (a ranking of perceived accessibility of the nest to mammalian predators based on water depths). During 2000, the year of the lowest spring water levels, more nests were located in cattail/bulrush, in deeper water, and in taller vegetation than in previous years. We estimated occurrence of renesting at 5% (1997), 2% (1998), 10% (1999), and 8% (2000). Nest success seems to be influenced by factors related to concealment (vegetation type and height) and predator access (isolation by water) or foraging opportunities (alternative prey), but not to land-use practices. Nest survival examined in 12 experimental units did not differ among 4 management practices (idle, fall burning, fall grazing, and a rotation of summer grazing and idle), but differed among years. Nest survival in 1998 (concurrent with a microtine irruption) was significantly higher than in 1999 and 2000 and slightly higher than in 1997. Differences in nest survival among land-use practices across the entire basin suggested nest success was higher on fall-grazed units than idled or summer-grazed units during 1997 and 1998, but no differences were detected in 1999-2000 when water levels were lower. Nests in cattail/bulrush had higher survival than nests in semi-wet meadow and Baltic rush habitats, but nest survival in 1997 and 1998, when water levels were highest, was similar across all 3 habitats. Nest success varied with isolation, but interactions between isolation, year, and other factors indicated that the relationship was complex. Apparent nest success of sandhill cranes during 1997-2000 ranged from 72% in 1998 to 51% in 2000, with an overall mean of 60% (41% Mayfield nest success; n = 519 nests). These rates are lower than that reported for 1949-1951 (90%; Steel 1952) and 1970-1971 (78%; Drewien 1973). We suspect that substantial changes in the predator community have contributed to declining nest success rates over the past 30 years.

Continued monitoring of crane populations during Spring and Fall and periodic monitoring of nest success is crucial because it provides the only objective standard for judging effectiveness of management practices and effects of natural or anthropogenic perturbations. We recommend maintaining the treatments on the 12 experimental units and collecting data for an additional 3-4 years to obtain more conclusive information about effects of land-use practices on nesting cranes. We also provide recommendations regarding monitoring, management activities, and continued research.


Back to Research
Return to Grays Lake Ecosystem Contents

Accessibility FOIA Privacy Policies and Notices

Take Pride in America logo USA.gov logo U.S. Department of the Interior | U.S. Geological Survey
URL: http://www.npwrc.usgs.gov/projects/grayslk/scrane.htm
Page Contact Information: Webmaster
Page Last Modified: Friday, 01-Feb-2013 18:01:45 EST
Reston, VA [vaww55]