Abstract
Simple SummaryChronic Wasting Disease is a deadly infectious disease affecting cervids that was discovered in Norway in 2016. CWD can transmit through environmental reservoirs and aggregation and spatial clustering of animals may affect transmission. Deer usually forage on scattered forage, but anthropogenic food sources are often concentrated in space, leading to spatial aggregation. We determined what caused red deer to revisit the same locations in the environment, and the extent to which this was caused by anthropogenic food sources. We document that the most visited sites were indeed anthropogenic, which opens potential avenues to disease mitigation.Herbivores like cervids usually graze on widely scattered forage, but anthropogenic food sources may cause spatial revisitation and aggregation, posing a risk for transmission of infectious diseases. In 2016, chronic wasting disease (CWD) was first detected in Norway. A legal regulation to ban supplemental feeding of cervids and to fence stored hay bales was implemented to lower aggregation of cervids. Knowledge of further patterns and causes of spatial revisitation can inform disease management. We used a recently developed revisitation analysis on GPS-positions from 13 red deer (Cervus elaphus) to identify the pattern of spatial clustering, and we visited 185 spatial clusters during winter to identify the causes of clustering. Anthropogenic food sources were found in 11.9% of spatial clusters, which represented 31.0% of the clusters in agricultural fields. Dumping of silage and hay bales were the main anthropogenic food sources (apart from agricultural fields), and unfenced hay bales were available despite the regulation. The probability of the clusters being in agricultural fields was high during winter. It may be necessary to find other ways of disposing of silage and enforcing the requirement of fencing around hay bales to ensure compliance, in particular during winters with deep snow.
Highlights
None of the spatial clusters had hay bales within the cluster site itself, but hay bales were within sight for 11.9% (n = 7) of the agricultural field clusters
11.9% of clusters contained anthropogenic supplements, which accounts for 31% of the spatial clusters in agricultural fields
This yields some potential for disease mitigation, pointing in particular to targeting periods with deep snow when red deer gather at low elevation
Summary
We know little about drivers and patterns of revisitation of animals to specific sites [2]. Such revisitation is sometimes used to infer, regarding memory and familiarity as playing a role for habitat selection [3], but revisitation may arise due to unaccounted habitat heterogeneity [4]. Clustering of animals and frequent revisitation at specific locations may cause risk of transmission of infectious diseases. Understanding patterns and drivers of spatial clustering is an important issue for disease management, as the extent to which anthropogenic sources cause such aggregation provides a potential avenue for disease mitigation
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