Estimating Wolf Abundance in Montana with a Multi-Model Approach

Sarah Sells, Post Doctoral Research Associate

Estimating wolf (Canis lupus) abundance is a key component of wolf management in Montana. Monitoring results help Montana Fish, Wildlife and Parks set management objectives and communicate with stakeholders and the public. Monitoring any large carnivore is challenging due to their elusive nature and low densities. This is particularly true for wolves in the Northern Rocky Mountains, as federal funding for monitoring has ended and a large population spreads monitoring efforts thin. Furthermore, there is frequent turnover of packs, and behavioral dynamics may have changed with harvest.

We are developing an improved Patch Occupancy Model (iPOM) to estimate wolf abundance in Montana. This approach incorporates an occupancy model, a mechanistic territory model, and an empirical group size model. Whereas previous approaches to estimating wolf abundance relied on costly, difficult-to-collect monitoring data, iPOM eliminates the need for intensive monitoring and introduces biological models focused on the mechanisms underlying territorial and social behavior. In a three-part process, the occupancy model first estimates the extent of wolf distribution in Montana, based on environmental covariates and hunter-reported wolf observations. The spatially-explicit mechanistic territory model predicts territory sizes using simple behavioral rules and limited data for prey resources, terrain ruggedness, and human density. Together, these two models for area occupied and territory size predict the number of packs in a given area. Finally, a pack size model demonstrates that pack sizes are generally positively related to local densities of packs, and negatively related to terrain ruggedness, local mortalities, and intensity of harvest management. Total abundance estimates for given areas are derived by combining the predicted number of packs and pack sizes. Upon completion of this work, iPOM will continue to be used to estimate wolf abundance each year in Montana.