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The amphibian chytrid fungus Batrachochytrium dendrobatidis has been implicated in boreal toad declines, although its overall effect on population dynamics is complicated by interactions with changing habitat conditions, population isolation, and other environmental stressors.

USGS researchers conducted mark-recapture studies of boreal toads from 2003 through 2018 at the Lost Trail National Wildlife Refuge in northwestern Montana to examine dynamics of this toad metapopulation. Estimates of male and female abundance decreased dramatically over the 16 years. Researchers found no evidence that disease affected male toad survival but detected striking decreases in recruitment of new males to the population, leading to a near-extinction event. Restoration of historical hydrology within the refuge likely adversely affected amphibian breeding habitat, and researchers hypothesized that these changes interacted with disease, life history, and other factors to restrict recruitment of new individuals to the breeding population over time. Results point to challenges in understanding and predicting drivers of amphibian population change. 

McCaffery, R.M., Russell, R.E., Hossack, B.R., 2021, Enigmatic near-extirpation in a boreal toad metapopulation in northwestern Montana: Journal of Wildlife Management, online,

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