Spatial and Temporal Analysis of Contact Rates in Female White‐Tailed Deer

Abstract

: White‐tailed deer (Odocoileus virginianus) are important game mammals and potential reservoirs of diseases of domestic livestock; thus, diseases of deer are of great concern to wildlife managers. Contact, either direct or indirect, is necessary for disease transmission, but we know little about the ecological contexts that promote intrasexual contact among deer. Using pair‐wise direct contacts estimated from Global Positioning System collar locations and joint utilization distributions (JUDs), we assessed habitats in which contacts occur to test whether direct contact rates among female white‐tailed deer in different social groups differs among land‐cover types. We also tested whether contact rates differed among seasons, lunar phases, and times of day. We obtained locations from 27 female deer for periods of 0.5–17 months during 2002–2006. We designated any simultaneous pair of locations for 2 deer <25 m apart as a direct contact. For each season, we used compositional analysis to compare land‐cover types where 2 deer had contact to available land‐cover weighted by their JUD. We used mixed‐model logistic regression to test for effects of season, lunar phase, and time of day on contact rates. Contact rates during the gestation season were greater than expected from random use in forest and grassland cover, whereas contact rates during the fawning period were greater in agricultural fields than in other land‐cover types. Contact rates were greatest during the rut and lowest in summer. Diel patterns of contact rates varied with season, and contact rates were elevated during full moon compared to other lunar periods. Both spatial and temporal analyses suggest that contact between female deer in different social groups occurs mainly during feeding, which highlights the potential impact of food distribution and habitat on contact rates among deer. By using methods to associate contacts and land‐cover, we have created beneficial tools for more elaborate and detailed studies of disease transmission. Our methods can offer information necessary to develop spatially realistic models of disease transmission in deer.

Evaluating Spatial Overlap and Relatedness of White-tailed Deer in a Chronic Wasting Disease Management Zone

“…Many host characteristics such as sex, age, relatedness, density, social group composition, inter-group movement and isolation can influence the duration and intensity of contacts and disease transmission [1], [3]. Understanding how contact rates and social organization influences disease transmission and spread is a challenging issue in disease ecology yet it is critical for disease management [2], [4].…”

“…Female white-tailed deer generally associate more closely with relatives than with non-relatives [8], [9], [10]. Although the nature and persistence of these interactions are still under study [3], [6], [7], this general pattern has widespread acceptance and is sometimes referred to as the “Rose-petal theory” [11]. However, deer social behavior, site fidelity, and spatial overlap can vary among different habitats deer density, and hunting pressure [12], [13], [14], [15], [16].…”

“…Ultimately, local transmission of CWD results from individual deer movements that lead to interactions with conspecifics or the environment. In particular, the degree of spatial overlap and contact among deer is likely to impact both direct and indirect transmission of CWD, and other infectious diseases such as bovine tuberculosis [3], [6], [22].…”

“…Although previous studies on deer spatial overlap have been conducted [3], [6], we provide the first study evaluating links between deer spatial overlap, measured using VHF telemetry data, and deer relatedness based on microsatellite genetic markers. Based on female social structure, we hypothesize that related deer have greater spatial overlap, and thus more direct contact, than unrelated deer in the same areas.…”

“…We also hypothesize that fawns, who are dependent on their mothers, will overlap with adjacent deer more strongly than yearlings or adults. These overlap areas, where multiple deer share space, are the most likely regions for either direct or indirect transmission of CWD [3]. As such, understanding the factors that determine the degree of overlap, and consequently the amount of direct contact, between deer will be critical to understanding and mitigating the spread of CWD and other infectious diseases.…”