Continental declines in North American small mammal populations

We initially speculated that non-tropical North American (USA and Canada) small mammal abundances might have increased over the past several decades due to declines in mammalian predators. To test this idea we assembled from small mammal researchers 818 time series of small mammal abundances, containing a total of 5317 individual abundance data points, for 66 species in 21 genera. The resulting database is the largest collection of multi-year abundance data for North American small mammals. We then used a hierarchical Bayesian modelling approach to estimate an overall abundance trend. Contrary to our initial speculation, we found strong support for an overall decline in North American small mammal abundance, with an estimated annual decrease of 3.6 %. Sixty species trends were negative while only six were positive. Given this decline and given that small mammals are important for ecosystem function as prey items, as predators, and for seed dispersal, we suggest conservation efforts should be directed to this generally neglected group. In particular, we need further work to uncover the causes and consequences of small mammal declines, and to develop mitigation strategies to avoid further declines in North American small mammals. • We conduct the first estimate of the overall trend in small mammal abundance in NA. • We find strong evidence for a continent-wide decline in small mammal abundance. • Conservation efforts to understand and mitigate small mammal declines are needed.