Habitat selection by sympatric ungulates in an agricultural landscape : implications for disease transmission and human-wildlife conflict

Abstract

As areas of agricultural production expand worldwide, complex zones of wildlife-agriculture interface present numerous benefits and challenges to farmers and wildlife managers. In western Canada, free-ranging elk (Cervus canadensis), mule deer (Odocoileus hemionus), and white-tailed deer (Odocoileus virginianus) make frequent use of cereal, oilseed, and pulse crops. However, cervid use of annual crops presents substantial socio-economic concerns for producers. Additionally, use of crops may facilitate cervids co-mingling and increase the risk of intra- and inter-specific transmission of chronic wasting disease (CWD).

The purpose of my thesis research was to determine the key environmental factors influencing the selection of agricultural crops by elk, white-tailed deer, and mule deer, analyze overlap in species’ selection, and develop predictive models to identify the spatial distribution of crop damage risk. In this study, I analyzed 19,069 damage claims paid by Saskatchewan Crop Insurance Corporation to Saskatchewan farmers for confirmed losses to annual crops (cereals, oilseeds, pulses) from 2000-2012 by elk, mule deer, and white-tailed deer. These data were used to conduct species-specific ecological niche factor analyses (ENFAs), which relate habitat variables within damaged sites to that of the surrounding landscape. The key habitat variables influencing selection of annual crops were then incorporated into resource selection probability function (RSPF) models. These models characterize and predict the probability of crop damage by elk, mule deer, and white-tailed deer, and each possible dual species combination. By integrating damage probability values and historical monetary values of regional crop production, I evaluated the risk of annual crop damage by each of the three species, and dual species combinations, across all sections of agricultural land in Saskatchewan.

The ENFAs revealed that elk and white-tailed deer selected for areas where a high proportion of farmland is seeded to oats, barley, canola, and alfalfa, while avoiding areas farther from protected areas, with a high density of paved or unpaved roads and a high proportion of open grassland. Alternately, mule deer favoured open grasslands, shrublands, and areas with a greater density of streams or water bodies, while avoiding areas where a high proportion of farmland is seeded to oats, canola, flaxseed, wheat, and barley. Areas at highest risk for annual crop damage by elk bordered the northern edge of the study area; mule deer damage risk was highest in south-western and central Saskatchewan; while white-tailed deer damage risk was highest in north-eastern and north-central areas of the province.

Identifying these specific associations between landscape variables, rates of crop damage, and associated species overlap may provide an important opportunity for agencies to develop cooperative management strategies to efficiently allocate mitigation resources. Efforts to prevent the selection of cereal, oilseed, and pulse crops by free ranging elk, mule deer, and white-tailed deer in Saskatchewan could prove to be a valuable step in not only minimizing crop damage and maintaining wildlife tolerance in rural communities, but also in managing the spread of chronic wasting disease throughout western Canada.