North American Beaver Castor Canadensis Research Articles

Acoustic monitoring shows invasive beavers Castor canadensis increase patch‐level avian diversity in Tierra del Fuego

Abstract The North American beaver Castor canadensis is an invasive species in the Tierra del Fuego Archipelago. Due to this biological invasion, Argentina and Chile signed an agreement to restore affected ecosystems by eradicating beavers. In southern Patagonia, the beavers’ ecological impacts are well studied, but there is a relative lack of information on how their invasion (and potential removal) could affect bird communities. In the southern portion of Tierra del Fuego's ‘big island’ (Isla Grande), we conducted passive acoustic monitoring and avian point counts in intact riparian forests, beaver ponds and beaver meadows (i.e. drained ponds) to assess spatial and seasonal differences in acoustic activity and avian abundance, species diversity and functional diversity. During spring and summer, acoustic activity was significantly higher in meadows than in forests, with ponds exhibiting intermediate values. Abundance and species diversity exhibited similar patterns, driven largely by resident passerines, while functional diversity tended to be highest in ponds, largely due to ducks and raptors. Effects were weaker in fall and winter. Acoustic metrics exhibited moderate to strong correlations with all point‐count‐derived metrics. Synthesis and applications. At the patch level, the avian community was more abundant and diverse in beaver‐modified habitats than in intact riparian forests, though communities in modified patches may not differ substantially from those in analogous natural open and wetland habitats. Dam breaching and pond drainage did not yield a return to an intact forest bird community, indicating that active reforestation may be necessary to restore avian communities to pre‐beaver conditions in the short to medium term, as sought by the binational agreement. Given the immense challenges of eradication and restoration, its social‐ecological costs and benefits—including those related to avifauna—should be thoroughly considered in establishing goals or indicators of success.

A non-invasive, DNA-based method for beaver species identification in Finland

For the ability to control an invasive species and to protect an ecologically similar native species it is essential to map the exact distributions of both species. This is difficult if the species are so morphologically similar that their identification in the field is almost impossible. In Finland, the invasive North American beaver Castor canadensis is spreading towards the range of the native Eurasian beaver Castor fiber and at present, these species are partly sympatric. Effective management of these morphologically similar species requires an efficient method for species identification, ideally one that is non-invasive. Non-invasive genetic methods are used in a wide variety of wildlife species, for example in the research of large carnivores. Feces are a good source of DNA for terrestrial animals, but for the semi-aquatic animals like beavers, feces are not the best option. However, environmental DNA (eDNA) has been successfully used to detect species non-invasively in aquatic and terrestrial environments. We developed a non-invasive, eDNA-based method to map the distribution of the beaver species in Finland and to investigate within-species genetic diversity. The eDNA was obtained from the feed remains (wood chips) from beaver forage sites. With the help of Citizen science, wood chip samples were collected from different parts of Finland. We used our eDNA method to identify the ranges of both beaver species. Additionally, the presence of Eurasian beavers in south-east Finland was proven for the first time. Our non-invasive eDNA method is an effective way to accurately identify the ranges of both beaver species and will allow for the control of the invasive North American beaver and conservation of the native Eurasian beaver in Finland.

Populations in stable and variable habitats: Green and common sandpiper in a beaver-influenced landscape

Stability of breeding habitat use and population variability was studied in two common wader species: green sandpiper Tringa ochropus and common sandpiper Actitis hypoleucos in a boreal lake area in southern Finland. The main natural driver of habitat disturbance in the area is an ecosystem engineer, the North American beaver Castor canadensis. We also studied the presence and abundance of green sandpipers before, during and after beaver-induced floods.In the studied landscape, the variable habitat created by beaver flooding appeared to have carrying capacity for a larger green sandpiper population than the more stable habitat for that of the common sandpiper. Common sandpipers made much use of the same lakes from year to year whereas the occupation of wetlands by the green sandpiper was more variable. The population of common sandpipers fluctuated more, although they inhabited the more stable environment. Green sandpiper pair numbers increased during beaver flooding, which suggests that they adapt rapidly to changes in breeding site availability. Some of the facilitating effects of the beaver appeared to remain 1–2 years after the flooding.

Ecosystem services provided by beavers Castor spp.

Abstract We aimed to recognise beaver‐produced ecosystem services and quantify their theoretical value for the entire Northern Hemisphere. Activity of the Eurasian beaver Castor fiber and the North American beaver Castor canadensis in the landscape provides ecosystem services and disservices. Services produced by beaver activity include water purification, moderation of extreme events, habitat and biodiversity provision, nutrient cycling, greenhouse gas sequestration, recreational hunting and fishing, water supply, and non‐consumptive recreation. Beaver‐produced services have not been compiled, analysed, or quantified previously. Each service we evaluated is worth millions to hundreds of millions of US dollars (USD) annually. Habitat and biodiversity provision (133 million USD), along with greenhouse gas sequestration (75 million USD), are particularly valuable services in absolute terms, while non‐consumptive recreation (167 USD ha−1) and habitat and biodiversity provision (133 USD ha−1) have the largest annual per‐hectare values. Our results can be used to broaden decision‐making and management perspectives, as we offer value estimates to wildlife managers and municipality planners for assessing local site‐specific beaver wetland values and the opportunities for their realisation. Implementing Payments for Ecosystem Services schemes offer a concrete way for societies to benefit from beaver‐produced services while concurrently compensating beaver‐produced losses accrued to landowners. Building such schemes offer long‐term realisation of ecosystem services and damage mitigation. This would lead to increased societal well‐being and increased conservation interest and efforts.

Population and distribution of beavers Castor fiber and Castor canadensis in Eurasia

Abstract A century ago, overhunting had reduced Eurasian beaver Castor fiber populations to c. 1200 animals in scattered refugia from France to Mongolia. Reintroductions and natural spread have since restored the species to large areas of its original range. Population has more than tripled since the first modern estimate in 1998; the minimum estimate is now c. 1.5 million. Range expansion 2000–2020 has been rapid, with large extensions in western and south‐central Europe, southern Russia, and west and central Siberia. Beavers are now re‐established in all countries of their former European range except for Portugal, Italy, and the southern Balkans; they occur broadly across Siberia to Mongolia, with scattered populations father east. About half of the world population lives in Russia. Populations appear to be mature in much of European Russia, Belarus, the Baltic States, and Poland. There is a significant population of North American beaver Castor canadensis in Finland and north‐west Russia. Most other 20th‐Century introductions of this species have become extinct or been removed. Recent DNA studies have improved understanding of Castor fiber population prehistory and history. Two clades, east and west, are extant; a third ‘Danube’ clade is extinct. Refugial populations were strongly bottlenecked, with loss of genetic diversity through genetic drift. Future range extension, and large increases in populations and in impacts on freshwater systems, can be expected. Beavers are now recolonising densely populated, intensely modified, low‐relief regions, such as England, the Netherlands, Belgium, and north‐west Germany. They will become much more common and widespread there in coming decades. As beavers are ecosystem engineers with profound effects on riparian habitats, attention to integrating beaver management into these landscapes using experience gained in other areas – before the rapid increase in population densities and impacts occurs – is recommended.

Fall and Winter Movement Dynamics of Naturally Produced Spring Chinook Salmon Parr in Two Neighboring Interior Pacific Northwest Natal Rivers

AbstractOverwintering Pacific salmon Oncorhynchus spp. are vulnerable to mortality. Ecosystem degradation exacerbates salmonid vulnerability to mortality; thus, knowledge of winter movement dynamics is essential for guiding holistic management and restoration to safeguard population viability. In northeast Oregon, long‐term population performance metrics (e.g., survival) exist for parr of two neighboring Chinook Salmon O. tshawytscha populations (Catherine Creek [CC] and Grande Ronde River [GRR]); however, knowledge of their winter ecology is lacking. Our objective was to spatiotemporally characterize the movements and rearing distributions of naturally produced CC and GRR spring Chinook Salmon parr during fall and winter. Using radiotelemetry techniques (October–February), we identified the movement dynamics of CC (2009–2012) and GRR (2014–2016) spring Chinook Salmon fall migrants (i.e., parr overwintering downstream from natal areas). For both populations, median weekly linear range (i.e., movement) was high during fall migration, while sedentary behavior was associated with anchor and surface ice. Fall emigration occurred during declining thermographs, while overwintering parr movement and water temperature peaks were proximate. Fall migrant CC parr predominantly overwintered in the upper Grande Ronde Valley (GRV), while GRR conspecifics primarily reared upstream from the GRV. Extensive portions of CC and the GRR were not included in either population’s 99% kernel density estimate (KDE); however, each population’s 99% KDE extended into the lower GRV. The GRR population’s 50% KDE (i.e., core area) was small and proximate to several North American beaver Castor canadensis impoundments, while the CC population’s core area was relatively large and situated in the upper GRV. Overall, CC and GRR fall migrant populations exhibited divergent rearing and movement patterns; however, each population’s winter core area was proximate to lentic‐like habitats (e.g., beaver ponds). For Chinook Salmon parr, natal‐stream‐specific overwintering ecology knowledge appears critical to guide winter habitat conservation and restoration, while management for lentic‐like habitats may be advisable throughout the Pacific Northwest.

Vertebrate Species Richness at Littoral Beaver Lodges in a Temperate Artificial Pond

AbstractThe North American beaver Castor canadensis is widely recognized for its ability to modify freshwater habitats and facilitate changes in community composition. However, the seasonal composition of terrestrial wildlife at littoral beaver lodges remains poorly described, even though beaver lodges are distinctive semipermanent features of the terrestrial–aquatic interface and thus important resources for wildlife. Over 17 months, we used camera trapping, weather data, and satellite vegetation data to determine how vertebrate species richness and seasonal changes in community composition are associated with beaver activity and beaver lodges in a temperate artificial pond. Our results indicate clear changes in the composition of beaver lodge visitors across seasons. Moreover, there was not a strong association of species richness with beaver activity, vegetative condition, or weather condition. Littoral beaver lodges are likely important foraging sites for a wide range of taxa throughout the year. Our findings highlight the importance of beaver lodges in facilitating seasonal interactions and variation in species composition. We hope our work can be used as a baseline to investigate the importance of beaver lodges in promoting diversity at the terrestrial–aquatic interface.

Effect of Beaver on Brook Trout Habitat in North Shore, Lake Superior, Streams

AbstractThe Brook Trout Salvelinus fontinalis is a native salmonid that provides a valued and productive sport fishery in northeastern Minnesota. Revival of North American beaver Castor canadensis (hereafter, “beaver”) populations since their near extermination and concern over their impacts on Brook Trout habitat prompted a reexamination of the complex ecological relationship where the two taxa interact. Suitable Brook Trout habitat is characterized by cold, spring‐fed water with silt‐free rocky substrate and abundant cover, all of which beaver may directly or indirectly affect. Data collection occurred on 79 stream sections (200 m each) and 21 beaver ponds spanning the North Shore of Lake Superior during the summer in 2017 and 2018. Habitat suitability index (HSI) models determined the average HSI and quantity of suitable Brook Trout habitat (m2/100 m2) at stream and beaver pond sites, and a bioenergetics model calculated Brook Trout growth availability (m2/100 m2) and mean growth (g/d) at stream sites. Classification regression trees identified significant thresholds at which beaver activity (e.g., number of dams upstream of sampled sites and beaver pond age) influenced the quantity or quality of Brook Trout habitat and growth. No significant variables were identified as affecting Brook Trout habitat or growth rates in stream sites. Alternatively, the quantity and quality of Brook Trout habitat in this region appeared to be influenced by microhabitat variables (depth, velocity, and temperature) that are eminent at individual stream sites. Brook Trout growth was strongly influenced by velocity (m/s) and mean prey concentration (mg dry mass/m3). Results indicated that 12 of the 21 sampled beaver ponds contained suitable Brook Trout habitat, with dissolved oxygen (mg/L) identified as a threshold. This study recommends focusing on individual stream characteristics and beaver pond dissolved oxygen concentrations to achieve desired Brook Trout habitat and aid in the development of management strategies pertaining to these two taxa in Lake Superior's North Shore streams.

A Review of Beaver–Salmonid Relationships and History of Management Actions in the Western Great Lakes (USA) Region

AbstractWithin the western Great Lakes (WGL) region of the USA (Michigan, Minnesota, and Wisconsin), the ecological impact that the North American beaver Castor canadensis (hereafter, “beaver”) has on coldwater streams is generally considered to negatively affect salmonid populations where the two taxa interact. Beavers are common and widespread within the WGL region, while coldwater streams that support salmonid populations are scarcer landscape features; as such, all three states currently prioritize the habitat needs of salmonids in portions of each state by conducting beaver control in coldwater tributaries. In this paper, we review the history of beaver–salmonid interactions within the WGL region, describe how this relationship and management actions have evolved over the past century, and review all published studies from the region that have evaluated beaver–salmonid interactions. Our review suggests that beavers’ impact varies spatially and temporally depending on a variety of local ecological characteristics (e.g., stream gradient and prevalence of groundwater inputs). We found that beaver activity is often deleterious to salmonids in low‐gradient stream basins but is generally beneficial in high‐gradient basins and that ample groundwater inputs can offset the potential negative effects of beavers by stabilizing the hydrologic and thermal regimes within streams. However, there was an obvious lack of empirical data and/or experimental controls within the reviewed studies, which we suggest emphasizes the need for more data‐driven beaver–salmonid research in the WGL region. Resource managers are routinely faced with an ecological dilemma between maintaining natural environmental processes within coldwater ecosystems and conducting beaver control for the benefit of salmonids; this dilemma is further complicated when the salmonids in question belong to nonnative species. We anticipate that future beaver–salmonid research will lead to a greater understanding of this ecologically complex relationship, allowing managers to be better informed of when and where beaver control is necessary to achieve the desired management objectives.

Invasive North American beaver Castor canadensis in Eurasia: a review of potential consequences and a strategy for eradication

Seven North American beavers Castor canadensis (Cc) were introduced into Finland in 1937 to supplement an ongoing reintroduction of the nearly extinct Eurasian beaver C. fiber (Cf). At that time, many zoologists recognised only one species. However, in 1973, chromosome counts (Cf = 48, Cc = 40) acknowledged two species, and Cc became an invasive alien. Recently, expanding populations of both species have converged on two fronts in Finland and northwestern Russia. According to Gause's competitive exclusion principle, two species with identical niches cannot coexist indefinitely. The imminent question is whether coexistence or competitive exclusion will ultimately result, with the possible regional extirpation or eventual extinction of Cf. We reviewed published cases of interspecies contact and compared their life history, ecology and behaviour. The few published incidences of contact were inconclusive with respect to competitive advantage. Body size is similar, but Cc litter size is slightly greater. Only minor differences in life history, ecology and behaviour were found to exist, suggesting nearly complete niche overlap. Though competitive exclusion resulting in the extinction of a native mammal by an alien congener at the continental landscape scale has been rare, the process may be difficult to detect due to potential time lags of centuries. Thus, there is a distinct risk that Cc may eventually competitively exclude Cf at all landscape scales. As no country in Eurasia obviously wants an invasion of Cc, and as most national conservation laws and international treaties forbid the spread of alien species, we advocate that the precautionary principle be adhered to and an attempt to eradicate Cc from Eurasia be seriously considered. Successful eradication is still possible if the will to do so exists. Here, we outline an eradication strategy.

Recovery and status of native and introduced beavers Castor fiber and Castor canadensis in France and neighbouring countries

ABSTRACT The Eurasian beaver Castor fiber suffered a drastic reduction in both geographical range and population size, due to human persecution, until the end of the 19th century. After the adoption of protection measures, natural expansion and reintroductions led to the recovery of this species over much of its European range. We review historical events that led to the recovery of beavers in France, and summarize the status of beavers in various river systems. Beaver establishment in France is a story of overall success: several major river systems are presently occupied, so that the species is no longer at risk in France. However, beaver recolonization took place in parallel with increasing human impacts on the environment. In addition to natural limiting factors, anthropogenic factors impeded beaver settlement in many areas. Today, beavers often occupy suboptimal habitats and, as a consequence, come into conflict with human activities. Effective solutions for preventing beaver damage include the restoration of riparian habitats to discourage crop damage and the provision of physical barriers to protect crops. Beaver populations reintroduced into France all originate from the relict Rhône population. However, in recent years, beavers from populations in neighbouring countries have been expanding into north‐eastern France. Therefore, our review of beaver origin and distribution in these countries may contribute to the development of appropriate national management strategies and towards important decisions, e.g. the decision to try to keep Rhône beavers genetically isolated, or to allow populations to mix. The recently discovered presence of North American beavers Castor canadensis in three countries surrounding France has raised an important issue. This species may out‐compete C. fiber in places where the species come into contact. A programme based on field‐trapping sessions and genetic analyses has recently been initiated in some western countries in order to eradicate this non‐native species.

The importance of aquatic vegetation in beaver diets and the seasonal and habitat specificity of aquatic-terrestrial ecosystem linkages in a subarctic environment

The extent and ecological significance of trophic linkages across ecosystem boundaries have been the subject of considerable recent research attention. North American beavers Castor canadensis engineer terrestrial influences in aquatic ecosystems by constructing terrestrial food caches near their lodges and aquatic influences in terrestrial ecosystems by building dams and flooding low lying areas. However, it is poorly resolved to what extent beavers rely on aquatic food sources and whether this reliance is greater during winter when ice cover physically confines beavers to aquatic habitats or during summer when warm, ice free water promotes the growth and accessibility of aquatic vegetation. Working in a subarctic region, we surveyed the abundance of aquatic and terrestrial food sources in and around lotic and lentic environments and estimated their contributions to beaver diets during open water and ice covered periods using carbon and nitrogen stable isotope analysis of hair samples. Ponds had four times more aquatic vegetation than streams, but terrestrial habitats around ponds had less than half as much shrub cover as habitats adjacent to streams. Beaver diets in this subarctic environment are estimated to be comprised of 60 to 80% aquatic vegetation, with beavers occupying ponds consuming more aquatic vegetation in winter than beavers occupying streams, which rely more on terrestrial shrubs cached near their lodge. Collectively, these results show how the influence of physical barriers on ecosystem linkages can be modified by habitat- and season-specific abundances of preferred resources and the potential for animals to consume food in ecosystems and seasons different from where and when the food was harvested.

Conservation of the Eurasian beaver Castor fiber: an olfactory perspective

Chemical communication in mammals includes an array of specific behaviours that are often ignored in terms of their potential relevance to conservation. Often used during territorial or social interactions between animals, chemical communication can also be used as a tool in reintroduction programmes. Reintroductions still exhibit high failure rates and methods to improve success should be investigated. The Eurasian beaver Castor fiber has been widely reintroduced across Europe after its near extinction in the 19th century. 2. Using olfactory studies in the beaver, we aim to demonstrate how scent transfers a range of information about the sender which can be used to monitor social and territorial behaviour along with general well-being. Scent manipulation can be used to reduce human-beaver conflicts, and aid reintroduction success through reducing stress and territorial conflicts, and by influencing dispersal and settlement. 3. Two species of beavers, the Eurasian beaver and the North American beaver Castor canadensis, occupy freshwater habitats throughout North America and in parts of South America, most of Europe and parts of Asia. Most of the reviewed literature concerns the wild Eurasian beaver, its chemical communication and con- servation; however, captive studies and those addressing North American beavers are also included. 4. Chemical communication is advanced and has been well documented in this highly territorial species. However, few studies directly link olfaction with conserva- tion practices. 5. Olfactory studies in beavers can provide non-invasive methods to monitor translocated animals and indicators of health. We conclude that chemical analysis, olfactory studies and behavioural manipulations involving semiochemicals have important impacts on conservation and can generate practical solutions to conser- vation problems including aiding animal capture, captive stress reduction, breeding pair formation and release site fidelity.

Do introduced North American beavers Castor canadensis engineer differently in southern South America? An overview with implications for restoration

ABSTRACT Twenty‐five pairs of North American beavers Castor canadensis Kuhl were introduced to Tierra del Fuego Island in 1946. The population has expanded across the archipelago, arriving at the Chilean mainland by the mid‐1990s. Densities range principally between 0.5–2.05 colonies/km. They have an impact on between 30–50% of stream length and occupy 2–15% of landscape area with impoundments and meadows. Beaver impacts constitute the largest landscape‐level alteration in subantarctic forests since the last ice age. The colonization pattern, colony densities and impacted area indicate that habitat in the austral archipelago is optimal for beaver invasion, due to low predator pressure and suitable food resources. Nothofagus pumilio forests are particularly appropriate habitat, but a more recent invasion is occurring in adjacent steppe ecosystems. Nonetheless, Nothofagus reproductive strategies are not well adapted to sustain high beaver population levels. Our assessment shows that at the patch‐scale in stream and riparian ecosystems, the direction and magnitude of exotic beaver impacts are predictable from expectations derived from North American studies, relating ecosystem engineering with underlying ecological mechanisms such as the relationships of habitat heterogeneity and productivity on species richness and ecosystem function. Based on data from the species' native and exotic range, our ability to predict the effects of beavers is based on: (i) understanding the ecological relationships of its engineering effects on habitat, trophic dynamics and disturbance regimes, and (ii) having an adequate comprehension of the landscape context and natural history of the ecosystem being engineered. We conclude that beaver eradication strategies and subsequent ecosystem restoration efforts, currently being considered in southern Chile and Argentina, should focus on the ecology of native ecosystems rather than the biology of this invasive species per se. Furthermore, given the nature of the subantarctic landscape, streams will probably respond to restoration efforts more quickly than riparian ecosystems.

Stream flow, salmon and beaver dams: roles in the structuring of stream fish communities within an anadromous salmon dominated stream

The current paradigm of fish community distribution is one of a downstream increase in species richness by addition, but this concept is based on a small number of streams from the mid-west and southern United States, which are dominated by cyprinids. Further, the measure of species richness traditionally used, without including evenness, may not be providing an accurate reflection of the fish community. We hypothesize that in streams dominated by anadromous salmonids, fish community diversity will be affected by the presence of the anadromous species, and therefore be influenced by those factors affecting the salmonid population. Catamaran Brook, New Brunswick, Canada, provides a long-term data set to evaluate fish community diversity upstream and downstream of an obstruction (North American beaver Castor canadensis dam complex), which affects distribution of Atlantic salmon Salmo salar. The Shannon Weiner diversity index and community evenness were calculated for sample sites distributed throughout the brook and over 15 years. Fish community diversity was greatest upstream of the beaver dams and in the absence of Atlantic salmon. The salmon appear to depress the evenness of the community but do not affect species richness. The community upstream of the beaver dams changes due to replacement of slimy sculpin Cottus cognatus by salmon, rather than addition, when access is provided. Within Catamaran Brook, location of beaver dams and autumn streamflow interact to govern adult Atlantic salmon spawner distribution, which then dictates juvenile production and effects on fish community. These communities in an anadromous Atlantic salmon dominated stream do not follow the species richness gradient pattern shown in cyprinid-dominated streams and an alternative model for stream fish community distribution in streams dominated by anadromous salmonids is presented. This alternative model suggests that community distribution may be a function of semipermeable obstructions, streamflow and the distribution of the anadromous species affecting resident stream fish species richness, evenness, biomass and production.

Ecological impact of beaversCastor fiberandCastor canadensisand their ability to modify ecosystems

The genus Castor comprises two species: the Eurasian beaver Castor fibre , and the North American beaver Castor canadensis . Both species suffered from overexploitation, but have seen a revival since the 1920s due to increased protection and reintroduction programmes. Increases in the populations and distributions of species that are able to modify ecosystems have generated much scientific interest. Here we review the available literature concerning the possible ecological impact of beaver species in the Old and New World. 2. Beavers, being ecosystem engineers, are among the few species besides humans that can significantly change the geomorphology, and consequently the hydrological characteristics and biotic properties of the landscape. In so doing, beavers increase heterogeneity, and habitat and species diversity at the landscape scale. Beaver foraging also has a considerable impact on the course of ecological succession, species composition and structure of plant commu- nities, making them a good example of ecologically dominant species (e.g. keystone species). 3. Nevertheless, the strength of beavers' impact varies from site to site, depending on the geographical location, relief and the impounded habitat type. Consequently, they may not be significant controlling agents of the ecosystem in all parts of their distribution, but have strong interactions only under certain circumstances. We suggest that beavers can create important management opportunities in the Holarctic, and this review will help land man- agers determine the likely outcome of beaver activity.

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.

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

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.