Movement and habitat selection of the Eurasian red squirrel

Abstract

Movement ability and habitat selection of individuals are highly significant in determining the size of a population and impact the range and survival of the entire species. Thus, the conservation and management of animal species requires an understanding of the movement and habitat selection in various environments. Human-modified landscapes often differ from the natural environment of a species and can be highly fragmented. For forest-dwelling species, urbanized areas in particular can pose threats to movement, as forested areas are scarce and separated by roads and buildings.

In this thesis I study how an originally forest-dwelling species, the Eurasian Red squirrel (Sciurus vulgaris) is accustomed to live in human modified landscapes and move in urban and rural environments. The red squirrel is an arboreal mammal common in the boreal coniferous forests, but recent findings have shown the population declining in Finland. The movements of juvenile red squirrels are followed by radio tracking, and habitat selection, dispersal distance and movement patterns are examined as a response to landscape structures.

The results from the urban environment show that juvenile red squirrels do not avoid roads during their dispersal. In addition, mortality due to vehicles was detected low. Although red squirrels prefer areas with more trees available than in the surrounding urban landscape, they often use sites with only few trees. At the home range scale, the used area did not differ greatly from the habitat composition of the available landscape. Habitat use of juvenile red squirrels differed between the phases of dispersal, including settling in areas with less deciduous land cover type than in the natal area. Thus, red squirrels are well adapted to use urbanized areas and their movements are not inhibited by roads.

I found surprisingly long dispersal distances for juvenile red squirrels in the rural study area, with the maximum being over 16 km. The dispersal distances in the urban area were approximately only a quarter of those observed in the rural area. The landscape structure affected the eventual dispersal paths made by juvenile red squirrels; in the rural landscape, dispersers favored spruce-dominated areas and avoided fields along their dispersal route, although they occasionally crossed even wide fields. In the urban landscape, red squirrels preferred areas with deciduous or coniferous trees. The movement steps made by dispersers were longer in the more hostile landscape compared to forested areas. Despite these effects on movement path, the landscape structure only had a minor effect on straight line dispersal distances moved from the natal nest. Even though the dispersal distances of red squirrels vary greatly, it is obvious that landscape structure plays only a very small role in these differences.

Most of the dispersing individuals compared potential sites for a home range before settling into the one they chose. However, in the rural study area, long-distance dispersing individuals did not compare potential sites and settled in the last site they visited. Landscape characteristics did not explain the number of revisits that individuals made to alternative sites, but the number of revisits declined with a site’s distance to the natal nest and the dispersal distance of individuals. The effect of landscape variables on decisions regarding where to settle was small, but surprisingly, in the rural area, juvenile red squirrels settled in sites with more built area compared to sites where juveniles only visited but did not settle in. The decision making during natal dispersal seems to be driven mainly by factors other than landscape characteristics and the search strategies vary between individuals and study areas.

In conclusion, juvenile red squirrels are efficient dispersers, and landscape structure has only a small effect on dispersal distances and thus possibly on gene flow of the species. Red squirrels are well-adapted to changing environments; in Finland, their movements are scarcely restricted by roads or unfavorable agricultural areas. The species can utilize urban environments and even exhibits a tendency to settle near human settlement in rural areas. This study has discovered a significant difference in dispersal distances between urban and rural environments, raising questions about the reasons behind extensive dispersal distances in the rural environment.