Drought leads to collapse of black-tailed prairie dog populations reintroduced to the Chihuahuan Desert

Background/Question/Methods

Black-tailed prairie dogs were once the most numerous species of prairie dog but have been reduced in distribution and abundance in the last 200 years. Recent conservation strategies emphasize reintroducing prairie dogs into Chihuahuan Desert grasslands of the southwestern United States, a region thought to contain large tracts of suitable habitat. The demographic responses of populations to these environments are largely unknown, but are important to achieving the management goal of repatriating prairie dogs and establishing viable populations. Because rainfall in desert habitats is lower, more variable, and incongruent with the reproductive biology of black-tailed prairie dogs, southwestern populations may be less prolific and fluctuate more than those in northerly climes. To assess their demographic response to climate, we used mark-recapture and mark-resight techniques to estimate population density, annual reproduction and monthly survival from 577 individual prairie dogs inhabiting six reintroduced colonies during three years in the Chihuahuan Desert. The study period spanned an extreme drought that occurred in 2003 when annual cumulative precipitation was 64% below the long-term average.

Results/Conclusions

Densities of these reintroduced populations averaged 11.3 prairie dogs/ha and were lower than average densities from more northerly climes ( = 18.3 - 90.3 prairie dogs/ha); population densities fluctuated widely in accordance with local environmental conditions. The probability that an adult female became pregnant, the number of juvenile prairie dogs emerging from maternity burrows, and their emergence time were positively linked to female body mass. Adult monthly survival declined abruptly from over 0.95 during the early spring to 0.70 in summer 2003, following a rapid loss in adult body mass that coincided with the low precipitation of 2003. Monthly juvenile survival fell to near zero on two of the three largest colonies in the same year and growth rates of juveniles in 2003 were half that of subsequent years. Reduced vital rates resulted in declines in population size at all colonies. Prairie dog populations in desert environs may be at greater risk of extirpation due to extreme fluctuations in population size caused by variable climatic regimes. Because the climate of the American Southwest is predicted to become hotter, drier and more variable, we suggest that the current conservation strategy to reintroduce black-tailed prairie dogs into the southern portion of their range needs to be reevaluated. Failure to do so may result in unfulfilled management objectives, misallocated resources and ultimately the continued decline of an ecologically important species.