Field Study Plan for "Voles, Ticks and Foxes" (Punkit, myyrät ja ketut)

Updated December 14, 2021 

Study goal. The aim is to clarify the interaction between ticks and mammals to develop natural and cost-efficient ecological control methods for tick-borne diseases. It is generally agreed among scientists that in an ecosystem, the amount of large mammalian herbivores regulates the amount of ticks, and that the amount of small herbivores and birds regulates the disease prevalence in ticks. In the case of the Nordic boreal forest, the most common small herbivores are the voles. Since people tend to favor herbivore game species, the amount of predators relative to herbivores is lower than in the food chain in a natural ecosystem.

In this study, I will study more closely a small part of the food chain that regulates disease prevalence in ticks. I am interested in how much red foxes affect the habitat use of voles which, in the presence of foxes, cannot freely roam all their preferred habitat, collecting ticks. From the tick point of view, this might mean fewer larvae developing into nymphs and less transfer of diseases, received and given.

Study sites. A number of study sites will be selected from the southern part of Finland. Each study site has either a healthy population of foxes or a hunted population with less foxes (acting as the control). In this area the primary land use is agriculture and it is climatically relatively homogeneous. Furthermore, it in the same phase of emergence, i.e. the incidence of tick-borne diseases in the Finnish population has been growing rapidly in the recent years. (The official disease statistics www.thl.fi). 

The study sites have different amounts of small cervids, i.e. white-tailed deer Odocoileus virginianus and roe deer Capreolus capreolus) which favor the least severe winter climate in the South. The whitetail was introduced into Finland from North America as a game species, and its does very well in the South-Western Finland as does also roe deer. Moose (Alces alces) is also common in forested areas. Main vole species in this area are bank vole Myodes glareolus and field vole Microtus agrestis. The area is dominated by agricultural land, which means that the interaction between field vole and red fox should be a dominant feature in the tick-host system. 

Field data collecting. Data collecting is done on each study site on a number of small mammal quadrants. The exact locations will be chosen based on the permits given by the land owners. Vole trapping is made primarily once a year in the spring. On each quadrant, mouse snap-traps will be placed for two nights in a row. Tick collecting is made on the same sites as the vole trapping with the dragging cloth method (mainly Ixodes ricinus in this area). The amount of foxes in the immediate vicinity of each trapping site is recorded in the winter by counting the amount of fox tracks after snowfall.