Latrine Foraging Strategies of Two Small Mammals: Implications for the Transmission of Baylisascaris procyonis

Abstract

The raccoon parasite Baylisascaris procyonis is implicated in the decline of the Allegheny woodrat (Neotoma magister). Baylisascaris procyonis is highly pathogenic in non raccoon hosts and is transmitted by eggs which are passed in raccoon feces. Granivorous species foraging for seeds in raccoon latrine areas risk exposure to the parasite. Various granivores exhibit different foraging behaviors, which may affect their probability of consuming B. procyonis eggs. To investigate the effects of species specific foraging strategies on the likelihood of B. procyonis transmission, I compared the latrine foraging behaviors of the white-footed mouse (Peromyscus leucopus) and the Allegheny woodrat during 1997 and 1998. The species use different foraging strategies, which result in differential risks of consuming embryonated B. procyonis eggs. Specifically, Allegheny woodrats carried whole feces to food caches, whereas white-footed mice primarily extracted seeds from the feces. Thus, woodrats run a greater risk of contaminating their entire cache with parasite eggs. In addition, woodrats did not collect fresh feces, but waited an average of 21 d before collection, while mice removed seeds immediately upon discovering the feces and preferentially foraged on seeds imbedded in fresh soft feces rather than on those in dried hard feces. This is relevant because B. procyonis eggs are harmless until embryonated, a process that takes approximately 2 to 4 wk. Therefore, mice reduce their risk by removing seeds from feces when the eggs are harmless, whereas woodrats increase their risk by waiting until eggs may be infective. These distinct foraging strategies help to explain the differential impact of B. procyonis on the two species.