Factors affecting seasonal movements of juvenile Greater Sage-Grouse: A reconceptualized nest survival model

• Published in: The Condor (Los Angeles, Calif.) Calif.), 2016-02, Vol.118 (1), p.139-147
• Main Authors: Caudill, Danny, Terhune, Theron M, Bibles, Brent, Messmer, Terry A
• Format: Article
• Language: English
• Subjects: Birds; Centrocercus urophasianus; Climate change; DEMOGRAPHY; Discriminant analysis; dispersal; Freezing; Greater Sage-Grouse; juvenile; migration; nest survival model; Ornithology; Population growth; Precipitation; Probability; Program MARK; seasonal movement; Seasons; Site fidelity; Snow accumulation; Survival; Survival analysis
• ISSN: 0010-5422; 1938-5129; 2732-4621
• DOI: 10.1650/CONDOR-15-77.1

Estimating the climatic and habitat factors that affect animal movement patterns (e.g., migration, dispersal, site fidelity) is informative for management and conservation. Juvenile Greater Sage-Grouse (Centrocercus urophasianus) have been identified as having a significant influence on population growth, but relatively little is known about factors that influence survival, movement, and the potential interrelation between the two. Movement out of fall habitat has been suggested to influence the survival of juvenile Greater Sage-Grouse. We reconceptualized the nest survival model (equating movement out of a focal area with failure of a nest) to extend its use to movement data on juveniles in south-central Utah. We found that juveniles' seasonal movements were affected by a linear trend in time (β = −0.655, 95% confidence interval [CI]: −1.049 to −0.26) and by precipitation (β = −3.718, 95% CI: −6.687 to −0.749), with an interaction between the parameters (β = 0.360, 95% CI: 0.002–0.718). In the absence of precipitation, the probability of movement increased weekly through time (within a year). Weekly precipitation increased the probability of movement in earlier weeks, but the effect of precipitation attenuated in later weeks (i.e. interaction parameter). The precipitation was likely non-accumulating snowfall, given the observed below-freezing temperatures. Our results suggest that changes in precipitation (mainly snowfall) that result from climate change could influence the timing and duration of seasonal movements (i.e. population-level time to complete movement) in migratory populations of Greater Sage-Grouse. Furthermore, our results demonstrate the utility of the nest survival model for evaluating the factors that affect animal movements with “ragged” data.