Lower Colorado River Valley Sandhill Crane (Grus canadensis) Breeding and Wintering Ecology

The Lower Colorado River Valley Population of sandhill cranes (LCRVP) is the smallest of the migratory populations of sandhill cranes. An identified management challenge with the LCRVP is uncertainty of its breeding origins due to intermingling and close proximity to other western sandhill crane populations (Rocky Mountain Population (RMP) and Central Valley Population (CVP)). Current coordinated winter aerial cruise surveys and ground counts conducted over 4 major wintering areas (Cibola National Wildlife Refuge (NWR), the Colorado River Indian Tribes wetland areas, Sonny Bono Salton Sea NWR, and Gila River) encompass ≥90% of this population. Approximately 30% of the cranes wintering in the LCRV have been located in the Nevada breeding range during the summer, leaving the remainder of the population unaccounted for during the breeding season. The primary LCRVP breeding areas are thought to be in northeast Nevada, specifically Elko and White Pines Counties. Because only 30% of the breeding population is currently accounted for on the wintering grounds there has been speculation that breeding occurs in other areas. Speculation regarding where LCRV cranes breed include: 1) western Utah, 2) south-central Owyhee County, Idaho (Mullins 1974), 3) southwestern Idaho (Drewien et al. 1976), and 4) Malheur County, Oregon. However, cranes in these areas belong to either the LCRVP or CVP (Littlefield and Thompson 1979). August (2011) suggested that federal and state lands in Nevada thought to encompass the breeding population may only contribute in a minor fashion to the overall population dynamics because suitable habitat may occur elsewhere, and there is little state and federal lands in the area favorable to breeding cranes. August (2011) found lower nest success rates on private lands (0.32 ± 0.08) in northeastern Nevada than either the Central Valley (0.72 ± 0.04, Ivey and Dugger 2008) or Rocky Mountain (0.41 ± 0.03, Austin et al. 2007; 0.65 ± 0.10, McWethy and Austin 2009) populations. This low nest success is inconsistent with recent estimates of recruitment on wintering LCRV cranes (Drewien and Rabe, personnel communications).