Drivers of long-term population dynamics of pronghorn in North Dakota

Background/Question/Methods

Over the past four decades, pronghorn (Antilocapra americana) populations in North Dakota have been exposed to rapid oil and gas development, agricultural land use change, severe winters, droughts, and varying levels of predation by humans and coyotes. The purpose of this study was to identify the key drivers of pronghorn population change in western North Dakota since 1974. We analyzed aerial survey count data using Bayesian mixed-effects models, with survey unit and year modeled as random effects. Fixed effects included winter severity, summer drought, coyote predation, abundance the previous year, road density, oil well density, agricultural land use, and year. 

Results/Conclusions

Preliminary results indicate that pronghorn abundance in July was low in years when drought conditions occurred the previous summer, and when preceding winters were severe. Pronghorn abundance was positively correlated with pastureland and sagebrush steppe habitat, and negatively correlated with road density. Oil development occurred in parts of the state with optimal habitat for pronghorn, causing a positive relationship between oil well density and large-scale patterns of abundance. Oil infrastructure is likely to degrade high-quality habitat for pronghorn and may be avoided at a finer scale. If winter precipitation increases as predicted by climate change models, then this, in combination with an extensive network of fences that prevents migration, will have a detrimental effect on pronghorn in North Dakota. The results of this study will help us to understand the vulnerability of this highly-valued North American ungulate to climate change as well as other anthropogenic factors.