Population dynamics of the northern short-tailed shrew, Blarina brevicauda: insights from a 25-year study

The population demography of the northern short-tailed shrew, Blarina brevicauda (Say, 1823), was studied for 25 years in bluegrass, alfalfa, and tallgrass habitats in east-central Illinois. The population in bluegrass had higher over-winter population density, began increasing earlier in the year, peaked earlier in the year, had higher mean monthly densities and amplitudes of fluctuation, and remained higher for longer than did populations in alfalfa and tallgrass. Survival rates were greater in bluegrass and tallgrass than in alfalfa. The species displayed annual population fluctuations with little variation in amplitude among years in all three habitats. Seasonal reproduction appeared to be responsible for the annual fluctuations. Survival did not vary in relation to season, but was positively correlated with annual peak densities, whereas reproduction was not. There was no correlation between population densities of voles during April–August and annual peak densities of B. brevicauda. We conclude that annual fluctuations in B. brevicauda populations are driven by seasonal reproduction, while variation in mortality, most likely from predation, may explain differences in the amplitudes of annual peaks.