Beavers in Scotland: consultation on the strategic environmental assessment

4.8 Beavers and other mammals

4.8.1 How beaver activity affects other mammals

Beaver activity may influence the local distribution and abundance of other mammal species in a number of ways, some of which may have a positive and some a negative effect on mammal species. In some instances these affects can be attributed entirely to the activity of beavers themselves. Some may be magnified when considered in-combination with the effect of other receptors. A summary (see Table 4.8.1) of these positive and negative effects of beaver activity on other mammals is presented at the end of this section. The main mechanisms are:

• By creating new areas of open water and associated wetland rich in aquatic plants, fish, amphibians and invertebrates, beavers can increase the availability of food for other mammal species. Many species that occur in Scotland, such as bats, water vole Arvicola amphibius and Eurasian otter Lutra lutra are likely to benefit from the creation of these new wetlands.
• Through effects on some invasive non-native mammals, notably American mink Neovison vison, which are also likely to benefit. However, there is evidence from Patagonia and Russia of American mink avoiding beavers, so the assumed habitat benefits to mink may potentially be cancelled out, at least to some extent, by such behaviour.
• Through the construction of lodges and the creation of burrow systems in riverbanks, beavers can create additional secure dens and resting places for other mammal species. Again, there are perceived benefits and disadvantages, as both native species, such as otter, and non-native American mink may utilise these structures, although how mink respond to the presence of beavers is not clear.
• By creating newly coppiced riparian woodland, the resultant opening of the woodland canopy is likely to be beneficial to some species, such as bats. However, the regrowth is also likely to attract herbivores, such as deer, which, if browsing rates are excessive, may ultimately inhibit the regeneration capacity of the affected woodland (see section 4.2.1. of this report).
• By creating channels through dense emergent vegetation (reed beds, etc.), beavers can potentially increase the permeability of these habitats to other mammal species. This could have both positive and negative effects. For example, there is evidence from England that water voles and American mink, which rarely coexist, can do so in dense reed beds as the mink tend to occupy the main water channels while the water voles occur in the more densely vegetated areas.

A recent review identified 35 published studies investigating the impact of beavers on terrestrial mammal diversity and abundance. Twenty-five of these studies suggested that terrestrial mammal species interact with beavers, either as predators or by making use of beaver ponds and other beaver-created habitat, but did not make a comparison with where beavers were absent. The remaining 10 studies investigated the differences between areas affected by beavers and areas where there was no impact from beavers. Beaver activity was found to have a positive effect on the abundance of a mammal species, or overall mammal diversity, in half of these studies, and no difference in the other half. No study found a negative impact of beavers on mammal diversity or abundance.

4.8.1.1 Beavers and bats

Four of the studies focused on bats, with two finding a positive impact of beaver activity. One Finnish study showed that ponds created by beavers supported a higher abundance of bats than other ponds. Bats are thought to benefit from beaver activity because of an increase in prey abundance and availability, and improved foraging habitat due to the creation of more gaps in the forest canopy.

In a Polish study, four species of bat that also occur in Scotland - the widespread and abundant common pipistrelle Pipistrellus pipistrellus and soprano pipistrelle P. pygmaeus and the much rarer noctule Nyctalus noctula and Nathusius' pipistrelle P. nathusii - were all positively affected by beaver activity. No impact of beavers on Daubenton's bats Myotis daubentonii was found, which is unexpected given that this species is particularly associated with water and frequently catches its insect prey directly off the water surface. In this case, the lack of any effect of beavers may have been due to a layer of duckweed impeding hunting on some of the beaver ponds in the study. However, the effect of beavers on Daubenton's bats may be either positive or neutral depending on the characteristics of the open water habitat created, and indeed an increased abundance of this species was found following beaver impoundment in another study. Beaver impoundments that result in waterbodies characterised by a smooth, uncluttered surface might be expected to benefit Daubenton's bats, as these provide an ideal foraging environment. When ponds created by beavers develop further to form beaver meadows, any benefit for Daubenton's bats seems to be lost.

Bats may also make use of beaver habitat in other ways, for instance by roosting under the exfoliating bark from trees killed by beaver flooding.

4.8.1.2 Beavers and otters

Otters are likely to benefit from beaver activity. Beavers increase the amount of aquatic habitat, and hence increase suitable otter habitat. The ponds formed are often rich in otter prey species such as fish, amphibians and invertebrates. Abandoned beaver lodges and bank dens may also provide important shelter for otters. Beaver-created habitat is an important predictor of North American river otter distribution.

While the majority of the literature focuses on the North American river otter, a number of reports also describe the benefit beavers have on Eurasian otter. As the positive mechanisms are associated with pond creation and the creation of shelter for resting sites, similar effects are expected for both species.

The Danish trial reintroduction of beaver to Klosterheden State Forest included an assessment of the effect on the resident otter population. No negative effects were observed on the otter population. The number of locations with evidence of otter presence has increased throughout the catchment following beaver reintroduction. After the beavers were released at the site, otter was put forward as a Habitats Directive Annex II interest at the SAC at Klosterheden, and it is the view of the Danish Forest and Nature Agency that the otter interest can be maintained in the presence of beavers.

4.8.1.3 Beavers and water vole

Beaver pond creation and herbivory has the potential to have a large positive influence on water voles in the absence of American mink. The water vole has experienced a dramatic population decline across Britain, particularly in the latter part of the twentieth century.

Reintroducing beavers would create and improve habitat for water voles, which have a strong preference for slow-moving water with abundant aquatic, emergent and herbaceous bankside vegetation; all features that are characteristic of beaver ponds. A key management technique used to improve water vole habitat is thinning woody riparian vegetation, an effect beavers can also create. Evidence for a positive relationship may come from the muskrat Ondatra zibethicus, which is ecologically similar and seems to derive benefit from beaver-influenced habitat.

4.8.1.4 Beavers and non-native invasive species (American mink)

Beavers may influence local America mink Neovision vison activity, as mink are known to use beaver lodges as den sites and beaver ponds for foraging elsewhere in Europe and in North America. The highest densities of mink (and otters) occur in productive coastal habitats, and therefore the potential for interaction with beavers may be limited.

Table 4.8.1: Summary of potential interactions between beavers and other mammals.

Activity	Mechanism	Positive effects	Negative effects	Notes
Felling	Change in riparian woodland: Opening of woodland canopy and increased patchiness	A more open woodland canopy improves foraging habitat for bats Increased light levels at water's edge may improve water vole habitat Overall positive effects on diversity at landscape scale since beaver activity markedly increases habitat heterogeneity and patchiness through the creation of canopy gaps, etc.		Water vole populations are expected to respond to improved habitat conditions only where American mink are controlled
Felling	Change in riparian woodland: Change in age classes of trees	Coppiced riparian woodland is likely to benefit many species Regrowth is likely to attract herbivores such as deer	Regrowth may be restricted where deer numbers are high
Felling	Change in riparian woodland: Amount/diversity of fallen dead wood on woodland floor	Uncertain, but may be beneficial impacts on prey species
Felling and constructions	Changes in amount/diversity of woody material in watercourses	Uncertain, but may be beneficial impacts on prey species, e.g. fish for otter
Dams/pond creation	Change from lotic to lentic habitat	Overall positive effects on diversity at landscape scale since beaver activity markedly increases habitat heterogeneity and patchiness, with lentic and associated wetland habitat interspersed with lotic habitat The creation of pond habitat will boost prey abundance for many bat species and otter	Non-native American mink may benefit from new pond creation	The water shrew may be influenced; however, it occupies both lentic and lotic habitats and the effects are unknown
Dams/pond creation	Change in hydrological processes on riparian and downstream habitat	The creation of new riparian wetland will boost prey abundance for many bat species and otter	Non-native American mink may benefit from new wetland creation
Dams/pond creation	Changes in water quality downstream	Uncertain, but may be beneficial impacts on prey species, e.g. fish for otter
Dams/pond creation	Change in standing dead wood resulting from inundation of trees	May provide roosting opportunities for bats
Dams/pond creation	Impacts on movement of species		Beaver dams may sometimes have adverse impacts on migratory fish species, with consequent localised impacts on otter	See Table 3.14 for effects of beavers on fish
Other constructions	Creation of lodges, burrows, canals etc.	Burrows and lodges will provide additional secure dens and resting places for a variety of mammal species	Non-native mink may utilise these structures Foraging trails increase accessibility to dense habitats used as cover, such as reed beds, potentially increasing predation
Other		Beavers (especially juveniles) may be a prey species for a variety of predators
Indirect habitat creation/restoration initiatives as result of beaver presence	Beaver used to promote opportunities for riparian and freshwater habitat creation/restoration	Presence of beavers may act as an incentive for greater investment, management and monitoring. This could include those related to the restoration and management of riparian woodland, which would benefit a range of mammal species, e.g. otter, water vole, bats, red squirrel

4.8.2 Distribution of mammals in the policy area

The following section concentrates on those mammal species of conservation importance that are likely to overlap with core beaver habitat and as such maybe positively or negatively affected by beaver activity.

4.8.2.1 Mammal species of conservation importance

To determine whether the activity of beavers on (native) mammal species is significant in the context of this Strategic Environmental Assessment, the assessment of impacts (positive and negative) has focussed on those species for which beaver activity may affect directly or indirectly (as discussed above), which are considered as having conservation importance and as such are afforded European or national protection wherever they occur.

In addition, the invasive non-native species, American mink Neovision vision has also been included in this section because of its overlap in some of its habitat and foraging requirements. Moreover many of the potential positive effects of beaver activity for mammal species of conservation concern are often in the absence of predation by mink.

Table 4.8.2 below therefore identifies those mammal species of conservation importance that utilise 'potential beaver core habitat' (as described in section 4.2. of this report) and are found within the beaver policy area. Red squirrel, has not been included as any impact from beaver felling activity is expected to be negligible.

Table 4.8.2: Summary of mammal species of conservation importance within the beaver policy area that overlap with potential beaver core habitat

Mammal species	Conservation importance
European otter	European Protected Species Qualifying feature of the following SACs: Ballochbuie SAC Cairngorms SAC Dunkeld-Blairgowrie Lochs SAC Loch Lomond Woods SAC Moine Mhor SAC Rannoch Moor SAC River Dee SAC River Spey SAC River Tay SAC Taynish & Knapdale Woods SAC Tayvallich Juniper & Coast SAC Notified feature of SSSI: River Spey SSSI
Bat species	European Protected Species
Water vole	Schedule 5 of the Wildlife & Countryside Act 1981 (as amended)
American Mink	Invasive non-native species

4.8.3 Assessment of likely effects on mammal species of conservation importance in the beaver policy area

Each of the species identified in Table 4.8.2 above is discussed in turn below in the context of those effects (positive or negative) that have been identified as a result of beaver activity. Where this relates to a species included in the Habitats Regulation Appraisal of the policy, a summary of the advice from SNH that has been provided to inform an appropriate assessment ( AA) of the policy with respect to SAC sites (see Annex 2 for the full advice) has been used (referred to hereafter as ' SNH HRA advice'). For the purpose of this assessment, the concluding points of the SNH HRA advice have been replicated where appropriate. Assessment of other sites (i.e. SSSI notified features), has been made in the context of the SNH HRA advice in combination with knowledge of the individual sites and their condition. Where mitigation or monitoring maybe appropriate, this has been identified in the narrative. Further discussion relating to the management of beavers including mitigation and monitoring options is provided in section 5 and 7 respectively.

Where a species is afforded protection as a European Protected Species through the Habitats Regulation 1994, consideration is given as to the policy impact on the favourable conservation status of the population of the species in its natural range.

Where mitigation or monitoring maybe appropriate, this has been identified in the narrative, with further discussion provided in section 5 and 7 of this report.

For species and habitats of conservation interest in the wider countryside there will be an ongoing need to assess data derived from general surveillance and monitoring activities that are already in place, and intervene with management if and when necessary. This will be informed by a more strategic approach to management being developed in due course.

Beaver opportunities

As mentioned above beaver activity has the potential to create many positive effects for a variety of native mammal species such as habitat creation or improvement with resulting benefits for prey abundance or foraging habitat. The presence of beavers could therefore act as an incentive for greater investment, management and monitoring. This could include those related to the restoration and management of riparian woodland, which would benefit a range of mammal species, including otter, water vole and bats.

4.8.3.1 Consideration of potential positive effects on mammal species of conservation importance

The impact of beaver activity on the mammal species discussed below is considered to be either positive or neutral. Where there is considered to be a negative effect or the potential for a negative effect, these are discussed in the following section, see 4.8.3.2.

European Otter

Otters are land mammals, but they spend a considerable amount of time in water. They can be found in both freshwater (such as rivers and lochs) as well as in the sea.

Otters live in holts, for example burrows, natural holes, caves or other structures (including man-made ones) that are used for shelter or for breeding. They can also use other structures to rest in or take temporary shelter, for example couches

A number of positive and negative effects have been identified for otter. Potential positive effects are anticipated to include:

• The creation of pond habitat will boost prey abundance for otter
• The creation of new riparian wetland will boost prey abundance for otter
• Burrows and lodges will provide additional secure dens and resting places for a variety of mammal species

Knapdale

• Moine Mhor SAC
• Taynish & Knapdale SAC
• Tayvallich Juniper and Coast SAC

Tayside

• Ballochbuie SAC
• Cairngorms SAC
• Dunkeld-Blairgowrie Lochs SAC
• Loch Lomond Woods SAC
• Rannoch Moor SAC
• River Dee SAC
• River Spey SAC
• River Tay SAC

Knapdale

Beaver activity in Knapdale can be expected to lead to the creation of further areas of wetland that will provide additional foraging resource for otters and (other species) reliant on wetland and riparian habitats. The extent to which this extra resource will actually benefit otters is difficult to judge, as the habitat in the SBT release area and nearby coast is already excellent for otters. The coast is likely to remain the focus for much of the otter foraging activity in the area. Should beavers expand north of the Crinan Canal into the River Add catchment, more tangible benefits to otters can be expected, as the SBT monitoring indicated that otter activity in this area was consistently less than in Knapdale with its more varied habitats.

Beaver activity can be expected to lead to the creation of additional otter holts and lie-ups (and dens for other species including the non-native mink, see below) in the form of disused and abandoned lodges and bankside burrows. It is unclear whether these extra places of shelter would actually influence the population density of territorial species at Knapdale. In the case of otters, for example, food supply is more likely to limit population density than the availability of holt sites or lie-ups.

Beaver activity can be expected to result in local increases in amphibian populations, which will benefit otters. Frogs and toads are important seasonal prey items for otters, notably at breeding ponds in the early spring. Fish form a significant component of otter diet, and fish surveys undertaken at Knapdale during the trial period found no significant change in the species composition or the number of fish found at sites where beavers have become active. Should further beaver releases take place in Knapdale, ongoing monitoring of the fish population would be recommended.

Tayside

In Tayside, further expansion of the beaver population is anticipated as the species colonises the remaining parts of the catchment where suitable habitat exists. Many habitats and species are expected to benefit, as noted above for the Knapdale area, with positive or neutral effects on native mammals, as summarized in Table 4.8.2 above.

European Protected Species

Otter are classed as European Protected Species, and are fully protected under The Habitats Regulations 1994 (as amended in Scotland).

While this assessment has identified the potential for some localised negative effects on otters, which are discussed in section 4.8.3.2 below, it is anticipated that the potential impacts from the policy will not be detrimental to the maintenance of the population of the species (otter) concerned at Favourable Conservation Status in their natural range.

Bats

There are at least ten species of bat to be found in Scotland. The most numerous and familiar of these are common and soprano pipistrelles, which can be seen flitting about near woodland or open water at dusk, in search of midges and other flying insects.

Potential positive effects are anticipated to include

• A more open woodland canopy improves foraging habitat for bats
• The creation of new riparian wetland will boost prey abundance for many bat species

Knapdale & Tayside

Beaver activity in the policy area can be expected to lead to the creation of further areas of wetland that will provide additional foraging resource for certain bat species reliant on wetland and riparian woodland habitats. Evidence from elsewhere in Europe strongly suggests that local bat populations will benefit from the activities of beavers in the area.

European Protected Species

Bats are classed as European Protected Species, and are fully protected under The Habitats Regulations 1994 (as amended in Scotland).

While this assessment has identified the potential for some localised negative effects on bats, which are discussed in section 4.8.3.2 below, it is anticipated that the potential impacts from the policy will not be detrimental to the maintenance of the population of the (bat) species concerned at Favourable Conservation Status in their natural range.

Water Vole

Water voles are the largest species of vole found in the UK, so big that they are often mistaken for rats. The water vole is a rare species that has suffered significant declines in population and range in the past. They live in burrows alongside, generally small, watercourses and feed on bankside grasses and sedges.

Potential positive effects are anticipated to include increased light levels at the water's edge which may improve water vole habitat

Knapdale

The water vole was included in the SBT monitoring programme, but no evidence of the species was recorded during the trial. This is not surprising given the unfavourable heavily shaded habitat at many of the locations where the surveys were undertaken, and the autumn and early winter survey period that was employed. A single sighting of a water vole was recorded by the SBT staff on Loch Linne in August 2012, suggesting that this species is present in the area, but at a low density.

Tayside

As noted above that, although habitat for water voles may improve as a result of beaver activity, they are unlikely to thrive if mink are present in the area. Predation by mink has resulted in the extinction of water vole colonies along most river main-stems and major tributaries in Scotland where the species previously occurred. The best populations are now mostly found in upland headwaters and are characterised by slow-flowing small burns meandering through areas underlain by deep peat. Potential beaver woodland habitat is usually absent at these sites.

Coordinated landscape-scale mink control projects, such as the Scottish Mink Initiative, have resulted in an apparent recovery of water voles in some areas which, if colonised by beavers, could allow water voles to realise the anticipated benefits of beaver activity. Overall, the current distributions of mink and water vole across Scotland suggest that there is likely to be a greater degree of overlap between an expanding beaver population and mink than with the more restricted water vole population.

The policy is not expected to results in any offence under the Wildlife and Countryside Act 1982 (as amended) to either of the beaver areas, for which water voles are listed on schedule 5.

4.8.3.2 Consideration of potential negative effects on mammal species of conservation importance

The impact of beaver activity on the mammal species discussed below is considered to have a negative or have the potential for a negative effect.

American Mink (Non-Native Invasive Species)

American mink Neovison vison, a semi-aquatic carnivore, first became established in the wild in Britain in the 1930s. Initially the population developed from animals escaping from fur farms, and throughout the second half of the twentieth century it spread through most of mainland UK. The spread of mink and their continued presence across many part of Scotland acts as a threat to many mammal (and bird) populations.

Beaver activity is likely to lead to an increase in the availability of prey for mink, notably invertebrates, fish and amphibians. However, the apparent avoidance of beaver-modified habitat by mink reported from Patagonia and Russia may potentially occur elsewhere and, if observed in Scotland, could have important implications for the future strategic management of mink in Scotland. Consequently, the interaction between the two species needs to be carefully monitored if further beaver expansion occurs; see section 7.

Assessment

Knapdale

Mink abundance in Knapdale (based on records of scats and footprints on mink-monitoring rafts) appeared to be low, although there is ample evidence from other studies that mink are abundant in coastal habitats in Argyll. The highest densities of mink (and otters) occur in productive coastal habitats, and therefore the potential for interaction with beavers may be limited. Control methods for this non-native invasive species are well established and are already in place at Knapdale and the wider area.

Monitoring

Further monitoring of the mink population would also be recommended, as it is unclear how this species will respond to an increasing beaver population, given the evidence from other parts of the world that suggests mink appear to avoid beaver- modified habitat. Mink monitoring would need to take place in areas where mink are both controlled and not controlled. See section 7 for details on the approach to SCM and beaver which would pick up the threat of this non-native species.

Tayside

Mink are already controlled throughout much of the Tay catchment, but it is unclear how an expanding beaver population might affect this species. If it transpires that mink, in fact, do not avoid beaver-altered sections of watercourses (as suggested by other studies) and actively utilise them, they could conceivably become easier to detect and control. This is because the rafts which form the basis of the Tayside control operation are best placed in still, slack water, such as that created by beaver activity.

Monitoring

Further monitoring of the mink population would also be recommended. See section 7 for details on the approach to SCM and beaver which would pick up the threat of this non-native species.

European Otter

Otters are land mammals, but they spend a considerable amount of time in water. They can be found in both freshwater (such as rivers and lochs) as well as in the sea.

Otters live in holts, for example burrows, natural holes, caves or other structures (including man-made ones) that are used for shelter or for breeding. They can also use other structures to rest in or take temporary shelter, for example couches

Knapdale

• Moine Mhor SAC
• Taynish & Knapdale SAC
• Tayvallich Juniper and Coast SAC

Tayside

• Ballochbuie SAC
• Cairngorms SAC
• Dunkeld-Blairgowrie Lochs SAC
• Loch Lomond Woods SAC
• Rannoch Moor SAC
• River Dee SAC
• River Spey SAC
• River Tay SAC

SNH HRA assessment

European beaver is a natural component of freshwater ecosystems in Europe, and beaver and otter are often recorded in the same areas. This is reflected by the fact that there are 396 SACs within the EU (within eight Member States) where both beaver and otter are both identified as Annex II SAC interests.

European beavers and otters do not compete directly for resources. The otter is a predatory species, and the beaver is herbivorous. Otter and beaver territories will overlap. There are occasional records of otter predation on beaver.

Information from Europe indicates that the presence of beavers does not appear to be detrimental to otters, and indeed may be beneficial. This is supported by the findings of the monitoring undertaken during the Scottish Beaver Trial. This is believed to be linked to the habitats that are created where beavers have been active, such as ponds, localised wetland areas etc., which are also good quality habitat for otters and otter prey.

However, beaver dams may sometimes have adverse impacts on migratory fish species which are one of the many prey species for otter.

The SNH HRA advice is that if the proposal is undertaken in accordance with the following mitigation condition, then the proposal will not adversely affect the integrity of the these sites.

Mitigation

Where beaver dams are constructed that impede the movement of migratory fish to such a degree that there might be an adverse effect on site integrity via impacts to otter, all appropriate mitigation measures to facilitate fish passage are put in place to avoid this.

Section 5 of this report details those techniques used to mitigate the impact of dam building activity including methods to alleviate the potential for impeding movement of migratory fish, should a situation arise where this is deemed likely.

EPS Assessment

Otter are classed as European Protected Species, and are fully protected under The Habitats Regulations 1994 (as amended in Scotland).

Although this assessment (see above) has identified the potential for some localised negative effects on otter, it is anticipated that the potential impacts from the policy will not be detrimental to the maintenance of the population of the species (otter) concerned at Favourable Conservation Status in their natural range.

Bats

There are ten species of bat to be found in Scotland. The most numerous and familiar of these are common and soprano pipistrelles, which can be seen flitting about near woodland or open water at dusk, in search of midges and other flying insects.

EPS Assessment

Bats are classed as European Protected Species, and are fully protected under The Habitats Regulations 1994 (as amended in Scotland).

Some bat species found in Scotland use trees for roosting either during the summer as maternity roosts to given birth and raise young or to hibernate during the winter. Colony size varies between species, but in Scotland bats are usually found either singly or in small groups in the winter, with slightly larger groups in the summer. There is therefore potential for a beaver to fell a tree (s) within the riparian (core beaver woodland) zone, that contains roosting bats, however the number of individual bats likely to be affected in is considered to be low.

Although this assessment has identified the potential for some localised negative effects on individual bats, it is anticipated that the potential impacts from the policy will not be detrimental to the maintenance of the population of the (bat) species concerned at Favourable Conservation Status in their natural range.