Reproduction by Black-Tailed Prairie Dogs and Black-Footed Ferrets: Effects of Weather and Food Availability

Food availability is one of the most important factors influencing reproduction in mammals. Reproductive success of some species can be negatively affected when body reserves are depleted during long periods of adverse weather conditions. We investigated the relationship of forage availability and weather variables on reproduction by black-tailed prairie dogs (Cynomys ludovicianus) and the effects of black-tailed prairie dog reproduction on reproduction by black-footed ferrets (Mustela nigripes), a prairie dog specialist predator. Prairie dogs draw on stored energy reserves to support reproduction (i.e., capital breeding), while ferrets likely rely on availability of prey during the reproductive period (i.e., income breeding). We expected that productivity of prairie dogs would positively correlate with precipitation during the previous summer and availability of spring forage and that harsh winter conditions would negatively affect reproduction. We also expected that productivity of ferrets would be positively correlated with productivity of prairie dogs because of the net increase in available prey during the ferret's litter-rearing season and because female ferrets might selectively prey on juvenile prairie dogs. At 2 sites in South Dakota during 2008-2010, reproduction by prairie dogs was most strongly influenced by precipitation received during the previous year and especially by winter severity. Harsh winter conditions resulted in a marked decline in reproduction during 2010. Although reproduction by ferrets varied little across years of our study, the success of long-term conservation and reintroduction strategies for the endangered black-footed ferret could be influenced by climate-driven changes in prairie dog reproduction.