Frank Rosell

Comeback of the beaver Castor fiber: an overview of old and new conservation problems

Abstract Due to over-hunting c. 1200 Eurasian beavers Castor fiber survived in eight relict populations in Europe and Asia at the beginning of the 20th century. Following hunting restrictions and translocation programmes in 15 countries, the Eurasian beaver became re-established over much of its former range, and presently numbers c. 430 000. The translocated populations often consist of a mixture of geographical forms. Preservation of the original, unmixed populations has therefore top priority: all five in Europe have reached the assumed minimum viable population size of c. 1880 animals each, but the three in Asia are still endangered. Their protection should be carried out at the level of river catchments. Nowadays the main threats for beavers are habitat destruction and introduced North American beavers Castor canadensis. On the other hand, growing beaver populations cause increasing conflicts with man, and population and/or damage control may therefore be required. In view of these two very different problems, we conclude that the conservation of beavers is best served by preservation and restoration of riparian woods with intact natural water regimes.

Scent-marking in the Eurasian beaver (Castor fiber) as a means of territory defense

Beaver (Castor spp.) normally scent-mark by depositing castoreum and/or anal gland secretion on scent mounds close to the waters edge. The aim of this study was to investigate the hypothesis that the Eurasian beaver (C. fiber) scent-marks as a means of territory defense. Scent-marking behavior was studied during an entire year (April 1, 1995–March 31, 1996) in seven adjacent territories along 9.2 km of the BΦ River in Telemark County, Norway. The number and location of fresh scent marks were recorded biweekly. The main results showed that: (1) the number of scent marks in territories was significantly higher in spring, when dispersal of subadults normally occurs than during the rest of the year; (2) the number of scent marks was clumped near territorial borders; and (3) the number of scent marks was significantly greater upstream than downstream of the lodge.

Mitochondrial phylogeography of the Eurasian beaver Castor fiber L.

Nucleotide variation in an approximately 490 bp fragment of the mitochondrial DNA control region (mtDNA CR) was used to describe the genetic variation and phylogeographical pattern in the Eurasian beaver (Castor fiber) over its entire range. The sampling effort was focused on the relict populations that survived a drastic population bottleneck, caused by overhunting, at the end of the 19th century. A total of 152 individuals grouped into eight populations representing all currently recognized subspecies were studied. Sixteen haplotypes were detected, none of them shared among populations. Intrapopulation sequence variation was very low, most likely a result of the severe bottleneck. Extreme genetic structure could result from human‐mediated extinction of intermediate populations, but it could also be an effect of prior substantial structuring of the beaver populations with watersheds of major Eurasian rivers acting as barriers to gene flow. Phylogenetic analysis revealed the presence of two mtDNA lineages: eastern (Poland, Lithuania, Russia and Mongolia) and western (Germany, Norway and France), the former comprising more divergent haplotypes. The low level of sequence divergence of the entire cytochrome b gene among six individuals representing six subspecies suggests differentiation during the last glacial period and existence of multiple glacial refugia. At least two evolutionary significant units (ESU) can be identified, the western and the eastern haplogroup. The individual relict populations should be regarded as management units, the eastern subspecies possibly also as ESUs. Guidelines for future translocations and reintroductions are proposed.

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

According to current theories of territoriality, an animal is expected to defend the smallest area that can provide resources for maximisation of reproduction, known as the ‘economically defendable’ area. In group territorial species however, the strategies behind resource defence are likely to be more complex with corporate territoriality, cooperative breeding, delayed dispersal and intra-group competition all potentially playing a role. Here we examined group territoriality in a social herbivorous rodent, the Eurasian beaver Castor fiber. Beavers in our study do not inhabit economically defendable territories. Instead the sequence of arrival of pairs into unoccupied areas seems to play a more important role in determining the size of the territory, whereas group size is determined by past reproductive success. We argue that the settlement pattern and reproductive history have a lasting impact in the territorial system of beavers due to a combination of the low adult mortality, high dispersal costs, and avoidance of resource depletion.

Use of anal gland secretion to distinguish the two beaver species Castor canadensis and C. fiber

Introduced North American beavers Castor canadensis pose a potential threat to the continuing recovery of Eurasian beaver C. fiber populations in several European countries. For management purposes, it is necessary to be able to identify and distinguish the two species. This, however, is difficult because the two species are morphologically, ecologically and behaviourally similar. To find a method for species identification, we examined the possibility of using anal gland secretion (AGS) collected from the two beaver species. We asked 20 inexperienced volunteers to inspect the colour and viscosity of the AGS. When we provided the volunteers with the sex of each beaver and descriptions of the colour and viscosity of AGS from males and females of the two species, all volunteers could 100% correctly identify the two species. We therefore conclude that the colour and viscosity of the AGS can be used for a quick and easy identification of the two beaver species.

Use of space and movement patterns in monogamous adult Eurasian beavers (Castor fiber)

Monogamy in mammals is characterized by reduced sexual dimorphism in morphology and behaviour. Ten pairs of Eurasian beaver Castor fiber were radio-tracked to test how far this concept can be applied to movement behaviour by focusing on sex-related effects on territory sizes and movement patterns. Within monogamous pairs, males and females occupied territories of almost equal size during the whole radio-tracking period and more specifically after parturition. The territories of pair members overlapped on average by 81.6 ± 14.0% SD while the territory overlap between residents and their neighbours was small to non-existent (on average between 0.5% and 2.2%). Males had larger 95% utility distributions than did females during the whole tracking period and after parturition. There was no significant difference between the 50% utility distributions for both sexes. Furthermore, males and females spent equal proportions of their time in territory border zones. There was a non-significant trend for males to move greater distances at night than females. Nightly distance moved correlated positively with territory size in females but not in males. Nightly distance moved correlated with neither body weight nor colony size. These results suggest that beavers show reduced sexual dimorphism in space use and movement patterns within adult monogamous pairs.

Selective foraging on woody plant species by the Eurasian beaver (Castor fiber) in Telemark, Norway

Beavers Castor spp. are generalist herbivores, feeding on the bark, shoots and leaves of woody plants, terrestrial herbs and forbs, ferns and aquatic vegetation. As central-place foragers, beavers move out from water to select and cut trees and vegetation, and then transport it back to their refuge. These terrestrial forays are energetically costly; therefore, beavers should concentrate their foraging activity near the central place and increase the degree of selectivity for specific sizes or species of food with increasing distance from the water. The aim of this study was to test the predictions of the central place and the optimal foraging theories for the food selection of the Eurasian beaver Castor fiber, and show the foraging preferences of the focal species in the boreal conifer forest zone of Europe. Foraging intensity by beavers and the abundance of woody species were surveyed in transects positioned randomly at seven beaver territories. In compliance with the central-place foraging theory, the foraging intensity declined with increasing distance from the river. Beavers fed preferentially on willows (Salix), rowan (Sorbus) and birches (Betula), although alders (Alnus) dominated their diet. Size selectivity showed similar patterns to previous North American studies, which were also carried out in habitats with predominantly small saplings. The probability of selection of small saplings dropped as distance increased, which is consistent with the predictions of optimal foraging models that larger prey items are more likely to be favoured with increasing provisioning distance.

Time budgets and sex differences in the Eurasian beaver

Abstract The Eurasian beaver, Castor fiber , is one of the few obligate monogamous mammal species known, and nothing is known about the time budget of the mated pair. We investigated whether mated adult Eurasian beavers would display sex differences in time budgets. Using radiotracking, we obtained behavioural data on six mated pairs of adult beaver during 2000 and 2001 on two rivers in southeast Norway. Time budgets for males and females were compared in total and over the seasons, along with temperature data collected throughout the study. The three main behaviours of both males and females were travelling, foraging and being in the lodge, accounting for 92.0 and 93.2%, respectively, of each sexs overall time budgets. Time budgets did not differ between the sexes except that males allocated more time to travel. Time budgets for each sex did not vary with season, and water and air temperature data were positively correlated with time spent travelling for both sexes. These results support the hypothesis that male and female time budgets are similar, except for the time that males and females allocated to travel. We suggest that the similarities in behaviour result because parental care by both parents is essential to the successful rearing of offspring, leading to reduced behavioural sexual dimorphism; nevertheless, some differences still occur, perhaps relating to the males indirect parental care. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Reference‐free SNP discovery for the Eurasian beaver from restriction site–associated DNA paired‐end data

In this study, we used restriction site–associated DNA (RAD) sequencing to discover SNP markers suitable for population genetic and parentage analysis with the aim of using them for monitoring the reintroduction of the Eurasian beaver (Castor fibre) to Scotland. In the absence of a reference genome for beaver, we built contigs and discovered SNPs within them using paired‐end RAD data, so as to have sufficient flanking region around the SNPs to conduct marker design. To do this, we used a simple pipeline which catalogued the Read 1 data in stacks and then used the assembler cortex_var to conduct de novo assembly and genotyping of multiple samples using the Read 2 data. The analysis of around 1.1 billion short reads of sequence data was reduced to a set of 2579 high‐quality candidate SNP markers that were polymorphic in Norwegian and Bavarian beaver. Both laboratory validation of a subset of eight of the SNPs (1.3% error) and internal validation by confirming patterns of Mendelian inheritance in a family group (0.9% error) confirmed the success of this approach.

Responses of foraging Eurasian beavers Castor fiber to predator odours

The ability of Eurasian beavers Castor fiber to recognise different predator odours has received little research, nor has the use of predator odours to deter Eurasian beavers from damaging agricultural crops, fruit and forest trees. Recognition of and response to predator odours by prey is of adaptive significance because it reduces predation risk. We tested the hypothesis that predator odours decrease foraging and predicted that: human and wolf Canis lupus odour would decrease foraging more effectively than other predator odours. Our results showed that all tested predator odours (red fox Vulpes vulpes, river otter Lutra lutra, lynx Lynx lynx, wolf and brown bear Ursus arctos), except those from human and dog Canis familaris, significantly decreased foraging during summer. River otter, red fox, lynx, wolf and brown bear odours had the strongest effects during summer. During autumn, river otter odour was significantly more effective than the other predator odours, except those from lynx, human and red fox, in decreasing foraging. Only odour from river otter, human, lynx and red fox had a significantly stronger effect than the three controls during autumn. Overall, the river otter odour was most effective in decreasing foraging. Odours from predators sympatric with the Eurasian beaver did not have a larger effect than those of originally sympatric, but now absent species. Beavers ate more sticks with predator odour in autumn than in summer. Our results have clear practical implications, and several are suggested.