The Effect of Federal Delisting on US Wolf Population Dynamics

Abstract

Species protection laws, like the US Endangered Species Act (ESA), are key tools for reversing biodiversity loss. One important question concerns whether legal protection can be phased out once a species is considered recovered and how this affects population dynamics. We used Bayesian hierarchical models and time series of annual population size estimates for gray wolves (Canis lupus) across eight US states to assess how annual population growth rates were affected by the proportion of each year that each wolf population was not listed under the ESA. We found that between 1979 and 2022, delisting had an overall negative effect on the growth rate of wolf populations. This effect remained after accounting for potential confounders like density dependence. The resulting growth rates after 1 year unlisted varied between the different states’ populations and included short-term declines as well as population stabilization and continued growth at slower rates over longer terms.