We studied a local population of mountain plovers (Charadrius montanus) in southern Phillips County, Montana, USA, from 1995 to 2000 to estimate annual rates of recruitment rate (f) and population change (λ). We used Pradel models, and we modeled λ as a constant across years, as a linear time trend, as year-specific, and with an additive effect of area occupied by prairie dogs (Cynomys ludovicianus). We modeled recruitment rate (f) as a function of area occupied by prairie dogs with the remaining model structure identical to the best model used to estimate λ. Our results indicated a strong negative effect of area occupied by prairie dogs on both λ (slope coefficient on a log scale was −0.11; 95% CI was −0.17, −0.05) and f (slope coefficient on a logit scale was −0.23; 95% CI was −0.36, −0.10). We also found good evidence for a negative time trend on λ; this model had substantial weight (wi = 0.31), and the slope coefficient on the linear trend on a log scale was −0.10 (95% CI was −0.15, −0.05). Yearly estimates of λ were >1 in all years except 1999, indicating that the population initially increased and then stabilized in the last year of the study. We found weak evidence for year-specific estimates of λ; the best model with year-specific estimates had a low weight (wi = 0.02), although the pattern of yearly estimates of λ closely matched those estimated with a linear time trend. Insouthern Phillips County, the population trend of mountain plovers closely matched the trend in the area occupied by black-tailed prairie dogs. Black-tailed prairie dogs declined sharply in the mid-1990s in response to an outbreak of sylvatic plague, but their numbers have steadily increased since 1996 in concert with increases in plovers. The results of this study (1) increase our understanding of the dynamics of this population and how they relate to the area occupied by prairie dogs, and (2) will be useful for planning plover conservation in a prairie dog ecosystem.
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Vol. 69 • No. 4