Landscape level variation in tick abundance and red deer migration pattern

Abstract

Over the past decades the population of red deer, Cervus elaphus, along the south-west coast of Norway have increased 10 fold in density as evidenced from the harvest statistics. At the same time the abundance of Ixodes ricinus ticks have increased. The increase in tick abundance causes major concern for the welfare of both humans and wildlife, but we still know very little about ticks. Previous studies have found a positive association between tick and red deer abundance. In addition, a negative association with altitude and distance from coast have also been documented for different tick species. In Norway tick abundance is an increasing problem. Still, there have been performed no study looking on which factors may explain the landscape level variation in tick distribution in Norway. Nor have any study investigated how the tick abundance is related to the space use patterns of red deer. Red deer at the west coast of Norway are known to show partial migration. Migration in red deer is assumed to be mainly related to differences in plant phenology induced by distance from the coast and altitude. However, also ticks likely show an uneven altitudinal distribution thus playing a yet unknown role in this migratory system. The aim of this thesis was first to quantify how tick abundance is related to factors such as time period, distance from coast and altitude, and second to quantify tick abundance at a landscape level relative to red deer migration pattern and local density of deer. To achieve this, tick abundance was surveyed by aid of the cloth lure method within winter and summer areas of stationary and migratory red deer during spring and fall 2009. A lower abundance of ticks with increasing altitude and distance from the coast was found. Surprisingly there were a negative relationship between tick abundance and red deer density. When looking on tick distribution relative to red deer migration pattern the density of ticks was higher in the home range of stationary deer relative to migratory deer. The smallest amounts of ticks were found in summer areas of migratory red deer. These findings gives support to the hypothesis that migration further away from the coast and to higher altitudes in the summer provide a benefit to red deer in terms of avoiding areas likely to yield heavy tick loads. This study thus give a better understanding of which factors influence the landscape level variation in tick distribution in Norway, and indicates that ticks may play a previous unknown role in the migration system of red deer.