Sandhill Crane Abundance and Nesting Ecology at Grays Lake, Idaho

Abstract

: We examined population size and factors influencing nest survival of greater sandhill cranes (Grus canadensis tabida) at Grays Lake National Wildlife Refuge, Idaho, USA, during 1997–2000. Average local population of cranes from late April to early May, 1998–2000, was 735 cranes, 34% higher than that reported for May 1970–1971. We estimated 228 (SE = 30) nests in the basin core (excluding renests), 14% higher than a 1971 estimate. Apparent nest success in our study (x̄ = 60%, n = 519 nests) was lower than reported for Grays Lake 30–50 years earlier. Daily survival rates (DSRs) of all nests averaged 0.9707 (41.2%). The best model explaining nest survival included year and water depth and their interaction. Nest survival was highest (DSR = 0.9827) in 1998 compared with other years (0.9698‐0.9707). Nest survival changed little relative to water depth in 1998, when flooding was extensive and alternative prey (microtines) irrupted, but declined markedly with lower water levels in 2000, the driest year studied. Hypotheses relating nest survival to vegetation height, land use (idle, summer grazing, fall grazing), and date were not supported. In a before‐after‐control‐impact design using 12 experimental fields, nest survival differed among years but not among management treatments (idle, fall graze, fall burn, and summer—graze—idle rotation), nor was there an interaction between year and treatments. However, DSRs in fall‐burn fields declined from 0.9781 in 1997–1998 to 0.9503 in 1999–2000 (posttreatment). Changes in the predator community have likely contributed to declines in nest success since the 1950s and 1970s. Our results did not support earlier concerns about effects of habitat management practices on crane productivity. Nest survival could best be enhanced by managing spring water levels. Managers should continue censuses during late April to evaluate long‐term relationships to habitat conditions and management.

Are Rice Paddies Suboptimal Breeding Habitat for Sarus Cranes in Uttar Pradesh, India?

“…During this study 11% of nests were second nests initiated 7-28 days after failure of first nests (mean 15.0 ± 3.7 days later) and located at a mean distance of 65.8 m (± 15.9, range 0-196 m) from first nests (Sundar and Choudhury 2008). In contrast to previous studies that had considerable difficulty in locating and confirming second nests (Austin et al 2007, Drewien 1973, in my study the probability of second nests being located was high. I minimized disturbance of nests by staying at the nest for <10 min during each visit and not using markers.…”

“…It is likely, therefore, that this study has detected an ecological trap. In Etawah and Mainpuri densities of Sarus Crane nests (0.79-0.91 nests km −2 ) were lower than estimated for cranes elsewhere (3.8-5.4 nests km −2 , Austin et al 2007). My calculation of densities of Sarus Crane nests includes habitats not used for nesting and is therefore an underestimate.…”

“…Among the cranes, the factors affecting nest survival are well documented for the Sandhill (G. canadensis) in the United States (Austin et al 2007, Dwyer and Tanner 1992, Littlefield 2003, Littlefield and Paullin 1990, Nesbitt 1988). Limited information is available for the White-naped Crane (G. vipio) from Mongolia (bradter et al 2005), and univariate analyses of factors affecting breeding success are available for the Sarus Crane in India (Mukherjee et al 2002, Sundar and Choudhury 2006, 2008.…”

“…This method is not advisable as a conservation protocol, however, since in many areas Sarus Cranes abandon nests if disturbed. Since most eggs were lost to humans, there was concurrent weak support for the effect of habitat variables on nest survival, which are important elsewhere (Austin et al 2007). this situation.…”

Nest Survival of American Coots Relative to Grazing, Burning, and Water Depths

“…Water depth also was found to be an important factor influencing nest survival of the earlier nesting species at Grays Lake, Sandhill Cranes (Grus canadensis; Austin et al 2007b) and Canada geese (Branta canadensis; Austin et al 2002). The importance of water depth may be amplified in this system because of rapid waterlevel declines during the nesting season.…”