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Reproductive Ecology of Greater Sandhill Cranes in Nevada
Natural Resources and Environmental Science
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We evaluated factors influencing survival of nests and chicks (i.e., colts) of greater sandhill cranes (Grus canadensis tabida) in northeastern Nevada, USA, during 2009-2010. We monitored 161 nests and 101 colts and used a maximum-likelihood based approach to test multiple competing hypotheses and estimate daily survival rates, nest success, fledging success, and covariates. Daily survival rates (DSRs) of nests were negatively related to density of crane pairs, and positively related to proximity to roads and vegetation height at nests. Low daily minimum temperatures had a negative effect on DSR, and the effect increased as incubation progressed. We found some support for a negative impact of summer grazing on DSR. Nest success in our study (32.3%, SE = 8.3%) was the lowest reported for sandhill cranes. Managers should encourage landowners to conserve wet-meadow habitat containing tall vegetation to enhance nest success of sandhill cranes. Areas with low-density nesting pairs may be particularly important for productivity, and should be given the highest conservation priority.We found colt survival was lower on Ruby Lake National Wildlife Refuge compared to private- or state-owned lands. Colts located on the Refuge had practically no prospect of fledging (1 ± 6% in 2009, <1 ± 3% in 2010), whereas colts located on private and state lands had higher and more variable probability of fledging (25 ± 13% in 2009, 15 ± 9% in 2010). Survival rates were lowest early in development and increased with age of colts. We did not detect an effect of weather or habitat use on survival. Our results support previous findings of predation as the primary cause of pre-fledging mortality in cranes. Our findings are inconsistent with sibling competition as a major source of colt mortality, but support extrinsic factors as important determinants of survival. Our results suggest that management of predator populations may influence fledging for cranes in northeast Nevada.