Grazing Effects on Deer Mice with Implications to Human Exposure to Sin Nombre Virus

We examined the effects of grazing on deer mouse (Peromyscus maniculatus) movements into buildings using passive integrated transponder (PIT) technology and small simulated buildings located on 0.6-ha treatment (grazing) and control (no grazing) plots. Twelve experimental 9-day trials were conducted over the course of the study. During these trials, mouse movements into buildings were monitored during three time periods (each 3 days in length). In the treatment plots these time periods corresponded to pre-grazing, grazing, and post grazing by horses. The number of individual deer mice entering buildings over time decreased in both the grazed and control plots during the 9 days of each experiment. The number of entrances per/individual among the pre-grazing, grazing and post grazing periods was different between control and treated plots for both males and females. The distribution of entrances/individual among the three periods differed between males and females in both grazed and control plots. The habitat modification caused by grazing appeared to reduce deer mouse activity (entrances/individual) in buildings but does not affect the number of mice entering buildings. Reducing vegetative cover by grazing or mowing may not affect the number of mice investigating small structures but grazing creates different activity patterns in the structures for neighboring deer mice.