Colonization, riparian habitat selection and home range size in a reintroduced population of European beavers in the Loire

Abstract

1. Colonization in a reintroduced population of European beavers in the Loire Valley was studied between 1974 and 1999. It followed a discontinuous remoteness model and a scattered distribution, beavers occupying only 25% of the river system over the 2800 km explored. 2. After 5 years, the colonization rate reached 104.2% year–1 of new sites occupied (SD 75% year–1), before dropping over the next 20 years. Nevertheless, the number of new colonies per km (0.125) remained stable throughout the years. 3. Populus nigra, Salix alba and Fraxinus angustifolia were the dominant woody species in beaver sites, often associated with some herbaceous species. 4. The length of willow grove dominated by S. alba and P. nigra (x) was the best predictor of beaver home range (y), fitting the equation y=−0.742x + 5.9. Long‐term maintenance of the population requires a minimum of 1.79‐km of willows per colony. 5. In cutting tree trunks, beavers stimulate shoot development from the remaining stumps. They rejuvenate riparian forests, increase the number of tree stems and help stabilize the banks. Their effect on woody plant morphogenesis may have consequences for the helophyte communities used as food or habitat by other aquatic species.

Distribution and patterns of spread of recolonising Eurasian beavers (Castor fiber Linnaeus 1758) in fragmented habitat, Agdenes peninsula, Norway

“…Single groups are relatively recently established on two more watersheds, and these have both selected high quality habitat patches. This pattern is in accordance with other studies, which show a pattern of rapid colonization within watersheds, strong selection for the highest quality unoccupied habitat available, progressive lowering of the quality of habitat on which settlement occurs as a watershed population grows, and a strong barrier effect of watershed divides on dispersal (Hartman 1994(Hartman , 1995Fustec et al 2001;John et al 2010;Halley et al 2002 for review). Beavers are known to have colonised site 2, on Skjenaldelva watershed, within 5 years of the initial release on Ingdalselva.…”

“…Both a male and a female would have to make the trip separately, as dispersal occurs as individuals. The furthest known colonisation distance previously recorded is of 80km, on the Loire, but this did not involve a watershed crossing and was on a river on which beavers were already firmly established (Halley & Rosell 2002;Fustec et al 2001). Conversely, persistence of a population which went unrecorded in print for over a century seems unlikely, even in so remote a location.…”

“…The topography and vegetation in the gorge is such that beavers could live in burrows with few obvious signs of presence, so it is possible these beavers may have been descendants of a remnant of the original population which survived at this location. Colonising beavers usually either occupy sites adjacent to existing territories, or make longer distance dispersals to patches of high quality habitat some distance from existing territories (Fustec et al 2001;John et al 2010;Halley & Rosell 2002 for review). The pattern in Ulsberg-Voll from the 1930s-1970s is consistent with shortdistance colonisations from a refuge in the gorge, which is then noted by the human population of the wider-bottomed river valley below.…”

Territory and group sizes in Eurasian beavers (Castor fiber): echoes of settlement and reproduction?

“…In fact, it appears that larger territories are also proportionately richer in terms of resource abundance. This is in contrast to a study on a newly established Eurasian beaver population in the Loire river valley, France that reports a highly significant negative correlation between home range size and proportion of suitable foraging habitat (Fustec et al 2001). In that study, home range boundaries were determined by investigating changes in density of beaver signs along the river rather than more directly by radiotracking or mapping scent mounds.…”

“…During natural colonisations of beavers in Sweden and France, distant sites were often colonised earlier than those closer to previously occupied sites, before filling up of the habitat took place (Hartman 1995;Fustec et al 2001). This pattern is analogous to a 22 sequential settlement.…”