Rabies and medium-sized carnivores

In 2001, a study of the ecology of medium-sized carnivores began in Virolahti, southeast Finland in order to collect data for rabies modeling in Finland. The home ranges, use of habitat, movements, contact rates and population densities of red foxes, raccoon dogs, European badgers and domestic cats were studied. The most important method employed was radio-tracking.

European rabies models are based on the ecology of the red fox, because foxes have long been the most important vectors of the disease in Europe. Finland experienced a short outbreak of sylvatic rabies in 1988–1989. Most of the victims at the time were raccoon dogs, but foxes, badgers and cats were also infected. Rabies models created for European conditions cannot be applied in Finland, because Finland contains several vector species. The research project conducted in Virolahti provides information on the ecology of medium-sized carnivores in order to model rabies epidemics in Finland.

The study of the animals found that the yearly home ranges were larger than the seasonal home ranges, because home ranges shifted somewhat between seasons. The seasonal home ranges of foxes were about 570 ha (yearly home ranges 660 ha). The home ranges of raccoon dogs were notably smaller, about 260 ha (yearly home ranges 390 ha). The European badger had the largest home ranges (670 ha, yearly home ranges 1470 ha). Cats lived in quite small areas, with the seasonal home ranges being only 100 ha and yearly home ranges 150 ha. Domestic cats (both pet cats and farm cats) lived in smaller home ranges than truly feral cats. The core areas of home ranges, where animals spent half of their time, were significantly smaller. The core area was 120 ha for the badger, 100 ha for the fox, 40 ha for the raccoon dog and 10 ha for the cat.

Overlapping home ranges of medium-sized carnivores in Virolahti. The picture
presents areas where animals spent 90% of their time. The movements of one
lynx were also radio-tracked. The home range of the lynx was divided into three
separate areas.

The raccoon dogs in the study lived in pairs and shared their home range with their mated pair, whereas home ranges of different pairs overlapped only by 32%. The home ranges of badgers also overlapped: on average, badgers shared 42% of their home ranges with conspecifics. In Virolahti, at least 8 badgers lived in overlapping home ranges. The members of fox families also shared their home ranges: 65% of their territory was shared.

Raccoon dogs and European badgers lived partly in the same home ranges. Because the home ranges of badgers were larger, they covered 73% of the raccoon dog home ranges, whereas the latter covered only 30% of badger home ranges. Cats also used same areas with other medium-sized carnivores. The home ranges of raccoon dogs covered 64%, and badgers 69% of the areas used by cats. The territories of fox covered 59% of the raccoon dog home ranges.

The home ranges and nightly routes of different individuals often overlapped. On the left, the overlapping home ranges and routes of two badgers in Virolahti between June and August 2002. On the right, routes of a raccoon dog pair.

Raccoon dog pairs spent their nights in a shared den. Sometimes a third raccoon dog hibernated in the same den. However, it was more common for raccoon dog pairs to share their den with badgers than with unfamiliar raccoon dogs. Badgers shared their setts with conspecifics quite often, both in the summer and in the winter. In one quite crowded sett, as many as two badgers and three raccoon dogs hibernated together.

The nightly routes of animals often crossed. The probability of contacts between animals was high. Raccoon dogs met their partner almost every night, but came across a neighboring raccoon dog only twice a month on average. Every third night a raccoon dog met a badger or a cat living in the same area. If an animal theoretically transmits a rabies infection effectively for three days, one infected raccoon dog could transmit the disease to two other raccoon dogs, four badgers and several cats. Respectively, one badger could infect three badgers, one fox and several cats. Thus rabies would quite likely be transmitted between species.

In southeast Finland the pooled population density of medium-sized carnivores is high: fox density (adults) is about 0.40/ km², raccoon dog density is up to 0.80/km², and badger density is about 0.28/ km². The pooled density of raccoon dogs and foxes is certainly sufficient for a rabies epidemic. Although they are considered just a ‘spill-over species’, badgers travel long distances and may transmit the infection to other species, especially raccoon dogs. The risk of a rabies outbreak is highest in the spring, when animals are moving actively. In winter and autumn, dispersing young foxes and raccoon dogs can easily transmit the disease to new areas.

A two-species (raccoon dog and fox) rabies model showed that rabies is not subject to spread if contained within a single species in Finland, but epidemics are very likely within the entire species community. The threshold density in a community of two vector species is low compared with the threshold of each of the species. Raccoon dog hibernation also influences rabies epidemiology.

The principal method employed in the study was the radio-tracking of medium-sized carnivores (the red fox, raccoon dog, European badger and domestic cat), which provided information about the contact rates between animals and their home range sizes and habitat use. Almost 50 animals were radio-tracked, and 43 of them provided enough information for estimating the home range size. Snow track counts were also used to estimate fox density. The modeling was done in cooperation with English scientists (the research group of Dr Graham Smith, Central Science Laboratory, York, United Kingdom).

Acknowledgements

We are very grateful to all the hunters who helped us with the fieldwork. We would particularly like to thank Tapani Rainio and the local hunters' association of Virolahti. Finland’s Ministry of Agriculture and Forestry took part in the funding of the project.

Scientist in charge of project

Kaarina Kauhala
Turku Game and Fisheries Research
Itäinen Pitkäkatu 3 A
FI-20520 Turku, Finland
Phone +358 205 7516921

Other research staff: Katja Holmala, University of Helsinki, Julia Schregel, University of Oulu, Alexander Singer & Graham Smith, Central Science Laboratory, York, UK

Duration 2000-

Scientific publications relating to the project:

Holmala, K. & Kauhala, K. 2006. Ecology of wildlife rabies in Europe. Mammal Review 36 (1): 17–36.

Kauhala, K. & Holmala, K. 2006. Contact rate and risk of rabies spread between medium-sized carnivores in southeast Finland. Annales Zoologici Fennici 43: 348–357. (PDF 256K)

Kauhala, K., Holmala, K., Lammers, W. & Schregel, J. 2006. Home ranges and densities of medium-sized carnivores in south-east Finland, with special reference to rabies spread. Acta Theriologica 51(1): 1–13.

Kauhala, K., Holmala, K. & Schregel, J.2007. Seasonal activity patterns and movements of the raccoon dog, a vector of diseases and parasites, in southern Finland. Mammalian Biology 72: 342–353.

Singer, A., Kauhala, K., Holmala, K. & Smith, G.C. 2008. Rabies Risk in Raccoon Dogs and Foxes. In: B. Dodet, A.R. Fooks, T. Müller, N. Tordo, and the Scientific & Technical Department of the OIE (eds.), Towards the Elimination of Rabies in Eurasia. Basel, Karger. Development of Biologicals 131, pp. 213–222.

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