How to recognise the presence of beavers?
Even if one can rarely observe beavers directly because of their nocturnal activity, different signs left behind by the animals during their activity allows to detect their presence with some certainty. Similar to signs of human activities, called artefacts, such signs can be named biofacts (as a biofact being an artefact made by a non-human organism).
The best season to search for beaver signs will be autumn and winter, because at this time woody plants will be utilised to a high degree, which will leave behind clearly distinguishable sings and because these signs can be seen clearly on the woody vegetation because of the lack of foliage.
Partly, other animals will leave behind signs quite similar to those of the beaver, so it is advisable not to search for only a single kind of possible beaver signs. If beavers are present in a certain area, one can always observe more than one type of signs.
The biofacts, which are usually to be found in the vicinity to a waterbody, are in detail:
The animal itself shows some characteristics, which allows the distinction of a beaver from the coypu and the muskrat, which are also living near the water and look quite similar:
This tutorial on the determination of beaver signs and the distinction of the three species beaver, coypu, and muskrat can as well be downloaded as a pdf-file (approx. 17 MB).
Cuttings [To the top]
First of all, cuttings can be found on different bushes and trees. Branches of woody plants with a diameter of
up to 10 cm are detached with an oblique cut, whereby the cut surface has an angle of approximately 45° towards
the perpendicular axis of the branch and shows clearly visible tooth marks. The cut surface of fresh cuttings
are of an almost white colour and therefore very conspicuous.
At the district Emsland, cuttings can normally be found on willows near the bank, but moreover also on other softwood species and even on conifers (e.g. pines). The majority of the cuttings are to be found in close proximity (approx. up to 10 m) to the next waterbody and at a hight of up to 1 m from the ground (however, if floods are frequent, cuttings can occasionally be found at distinctly larger heights). Care has to be taken in assigning the observed cuttings to a certain animal species, if only small branches up to the diameter of a human finger are to be found, because coypus and muskrats use smaller branches as food. Are none of the other beaver signs described over here can be found, it is almost certain that this are not biofacts of the beaver.
Mainly during the summer also herbaceous plants are cut by an oblique cutting but this can only assigned with great difficulty to a beaver, because several other animals (coypu, muskrat, Norway rat, hares, rabbits) cut herbaceous plants in a similar way.
Felled trees [To the top]
Trees or stems of larger bushes are felled by double-conically gnawing the stem if the stem diameter exceeds 10 cm
(the resulting form resembles that of an hour glass). This is an unambiguous hint to the presence of beavers, because
no other native animal species is felling trees in a similar way. In the district Emsland mainly deciduous trees like
willows poplars, birches, ashes, hackberries and oaks are felled, but also (mostly younger) conifers like pines or
blue Douglas firs. Felled trees can sometimes be found within greater distances (up to 20 m and occasionally more) from
the next waterbody.
More details on how beavers fell a tree, which tree species are used and how far the animals move away from the water to fell a tree can be found in the chapter Diet.
Gnawing traces [To the top]
Gnawing traces on still living woody plants can be found when beavers partly gnaw the bark of thicker branches or trees to
consume the bark (sometimes just to degust it) or if the animals are planning to fell a certain tree. Frequently the comparably
broad tooth marks of the incisivi can be clearly recognised.
If beavers plan to fell a tree, the bite relatively large woody chips (the size depends on the hardiness of the wood) from the stem, which can be found at the base of the tree,
Care has to be taken as well when detecting gnawing traces, because also coypus sometimes chew off bark from woody plants. The discrimination of the tooth marks based on their breadth is not very reliable, because the body size of coypus and beavers (and therefore the breadth of their incisivi as well) overlap to a large extend. If only very small tooth marks on predominantly thin twigs are observed, also hares come into question for this.
Decorticated sticks [To the top]
Larger cut branches are generally carried to the bank by the beaver and are debarked over here (only the bark will be
consumed). The debarked branches are left at the bank (xylem fibres can not be digested by the beaver). Currently
debarked branches are almost white in colour and therefore very conspicuous and easy to be find. Frequently to debark
branches, beavers visit the same spot at the bank, so after some time a considerable amount of debarked branches will
accumulate over there. Such spots are sometimes called feeding places and are very conspicuous. Occasionally, debarked
branches can be found at some greater distance from the bank: in such cases, usually the water level of the waterbody
has been higher (due to a flood) and the waterline has run at the area where the decorticated sticks were found. Sometimes
the animals are feeling so secure, that they quit feeding close to the water (in case of danger, beavers retreat into the
Even if decorticated sticks have been discovered, one can not automatically presume the presence of beavers, because also muskrats and coypus consume the bark and leave the debarked branches behind at the bank as well. Mainly if only single decorticated sticks were found, very often these are not left behind by beavers.
Food raft [To the top]
Partly, beavers build a food storage, which is comprised of branches stored below the waterline. However, such a storage will
only be build if severe winters are to be expected - because of that, at our latitudes food rafts can seldom be found. In
contrast to an accumulation of decorticated sticks, all branches of a food raft still wearing their bark. When creating a food
raft. some branches are fixed in the substrate of the waterbody to prevent the drifting away of the storage by the current. To
keep the raft below the water surface, the branches of preferred woody food plants (willows, poplars, etc.) are covered by
branches of less preferred woody plants (e.g. European black alder).
More details on the construction of food rafts can be found in the chapter Diet.
Exit [To the top]
Because beavers use the same spot over and over again to leave the water, after some time clearly visible gaps will develop especially
at steep banks.
However, also in this case it has to be noted, that also muskrats and especially coypus create similar exits at the bank. Although the exits created by muskrats can be easily distinguished because of the smaller size from those of the beaver, this will be not that easy in case of exits created by coypus. The differences in size between exits created by beavers or coypus will be more and more visible, the longer an exit is in use. Older beaver exits show a breadth of 30 - 40 cm and more, whereas exits used exclusively by coypus rarely reach more than 20 cm in breadth. Even roe deer (or other even-toed ungulates like wild boar or less frequently red or fallow deer) may create similar exits as beavers and coypus, in case they repeatedly cross a waterbody at the same location. However, in such cases the more or less distinct tracks of the even-toed ungulates can be recognised. Moreover, even fishermen can cause incisions in the bank by repeatedly visiting preferred fishing spots, which look - at a first glance - very similar to beaver exits. Now and then, beavers are also using the "fishermen exits" or the fishermen the beaver exits respectively.
In case of doubt, just by the presence of exits does not necessarily indicate the presence of beavers. In cases like that, one should try to find further biofacts of the beaver.
Trail [To the top]
Quite often the exits are followed by clearly visible beaten tracks on land: the so called trails or runways, which either lead towards
adjacent waterbodies or to preferred food sources of the beaver or which are used to bypass obstacles (e.g. weirs, rock ramps or
similar). Such trails also result by the repeated use of certain path by the beaver over an extended time period. Depending on the soil
condition, animal tracks or the drag mark of the tail may be visible (which of course facilitates the assignment) or not.
Such trails can also be created by coypus or by humans as well, so care has to be taken as well when assigning such a trail to a beaver.
Scent mound [To the top]
Beavers are territorial, which means that the family members are defending a part of their habitat (their territory) against
conspecifics. Scent marks are deposited for the delimitation of their own territory against animals not belonging to their
family. Moreover, the animals may use these scent mounds for their own orientation within their territory (for instance for
marking preferred food sources).
For the creation of a scent mound, a small mound is formed out of some soil (sometimes also grass or leaves) with the hands and the secretion of the castor sacks (the so-called castoreum) and/or the anal glands is deposited on top of the mound. Sometimes also decorticated sticks are incorporated into the scent mound (it is not known, if this is be done deliberately or by accident). The function of the scent mounds (respectively the castoreum or anal gland secretion deposited) will be discussed in the chapter Social behaviour in greater detail.
A scent mound created in the previous night can be perceived by a human by the characteristic smell of the castoreum from a greater distance without even actually seeing the scent mound. However, the intensity of the smell decreases rapidly for humans, for instance when it has rained during the night.
Form [To the top]
During their nocturnal activities beavers frequently take some short breaks. For this purpose, semi-circular dents were dug into
the bank, which are partly - similar to the nest chamber of the burrow - cushioned with wood shavings or frayed out grasses. At
times, also natural cavities in the bank (for instance under bigger tree trunks) are used as resting places by the animals. Such
temporary resting places are called forms.
Generally, these forms are difficult to find from the landside, because they are frequently build by the beavers underneath dense bushes. They can be observed somewhat easier by using a boat.
Based on their size (the cavities can reach a diameter of 50 cm and more), these forms are a strong indicator for the presence of beavers. However, also coypus sometimes build temporary resting places at the bank, which are cushioned by frayed out plant material as well and therefore can be confused with the forms of beavers. Usually, these "coypu forms&uot; are part of a burrow (they are only the entrances or exits of a coypu burrow). Moreover, coypus are known to sometimes build open-top forms in the dense, herbaceous bank vegetation. In contrast to this, beaver forms always offer the animals inside a certain amount of protection against the top (usually beavers do not build open-top resting places).
More details regarding the building of forms can be found in the chapter Building behaviour of the beaver.
Burrow [To the top]
Inside the burrows build by the beavers the animals spend their day and give birth to the kits as well. Permanently inhabited burrows
can be divided into three types - depending on the condition of the bank: the bank den, the bank lodge and the lodge. Temporary used
burrows are known as so-called flood burrows, which can be distinguished from the three other burrow types by the fact, that the
burrow entrance lies above the water surface during normal water levels, whereas the burrow entrances of all other three burrow types
lies below the water surface (the animals have to dive to enter or leave the burrow).
Schematic drawings and further details on the construction of burrows and lodges are given in the chapter Building behaviour of the beaver.
[To the top]
As far as possible, beavers will build bank dens. To achieve this, a tube will be dug from under water oblique upwards into the bank, which will be enlarged above the waterline to a nest chamber of about 1 m in diameter. Sometimes, additional entrances and exits are build subsequently.
Despite the size of such bank dens, they are very difficult to detect. As a rule, they can only be found when they have collapsed and have been abandoned by the animals.
[To the top]
If the bank, in which the bank den has been created, is relatively shallow, sometimes the ceiling of the nest chamber collapses, if the beavers dig to far upwards when building their bank den. Such cases do not necessarily lead to an abandonment of the burrow, but to the covering of the resulting hole with branches. Depending on the structure of the bank and the duration of the colonisation, either only some few branches are accumulated or a very large amount of branches are piled up. Such a burrow is then termed bank lodge.
Such bank lodges are relatively easy to find, although it can also easily been with a pile of branches, which has been collected after the pruning of trees by humans. However, the building material of a bank lodge mainly consists out of branches cut by the beaver, which shows characteristic tooth marks at the cut surfaces. Frequently, also the decorticated sticks are used as building material by the animals. Moreover, approaching the winter, the burrow will be sealed with mud by the animals. This allows the differentiation between a bank lodge and a pile of branches left behind by humans.
[To the top]
If the bank is very shallow, so that the construction of a bank den or a bank lodge is not possible, the beavers will build a free-standing lodge. Such a lodge completely consists out of piled up branches, in which an entrance will be gnawed from below, and which will be enlarged to a nest chamber above the waterline by the animals. Such lodges can reach - especially when they are being used over an extended period of time - an impressive size. However, in the district Emsland this burrow type can only rarely be found so far.
[To the top]
Muskrats can build lodges as well, which are sometimes mistaken for the lodge of a beaver. In comparison to beaver lodges, muskrat lodges are much smaller and consist exclusively out of herbaceous plant material (frequently out of the stalks of common reed and cattail).
[To the top]
Sometimes, during regular water levels, beaver burrows can be found, which are situated at some distance to the next waterbody and whose entrance is openly accessible. This is most probably a flood lodge, which was created by the beavers during a long lasting flood and abandoned after the decline of the water level. Such lodges can be used more than once during recurrent flood events; so the animals do not build a new flood lodge at every flood.
Dam [To the top]
A beaver dam is a transverse structure in flowing waters consisting out of branches, which is constructed by beavers to control
the water level. Partly, the dam is also sealed with mud. The function of the dam is to keep the entrance of the burrow or the
lodge permanently below the water surface and/or to enable the animals to reach preferred food sources by swimming.
The breadth and height of a dam can strongly vary depending on the circumstances. Usually, beavers are very efficient in achieving the largest effects with as little effort as possible: i.e. a dam will be build at places, where the creation of the smallest dam possible leads to the flooding of the largest area possible. However, the animals are able to create very large dams as well, which are often maintained over several years and generations. The largest beaver dam so far was discovered in 2007 in Canada at the province Alberta at the Wood-Buffalo-National Park south-west of Lake Claire (coordinates: 58°16´15.27" N 112°15´07.10" W). The dam approximately 830 m long can even be seen on satellite images (the effects of the dam on its surroundings can be seen on the satellite image - the dam itself of course is not to be seen!). Further informations on this and other beaver dams in Canada can be found over here.
Moreover, further details on the construction of dams can be found in the chapter Building behaviour of the beaver.
Occasionally, in small flowing waters, branches are washed up which become entangled and form a barrier. A certain blockage effect can result, if leaves and other plant materials get caught within the branches. If the branches are missing the typical teeth marks, beavers can be excluded from building this "dam".
Distinctive features on the animal [To the top]
Occasionally, not only signs are found but living animals are observed directly. Although beavers, coypus, and muskrats are very similar regarding their appearance and their behaviour (the members of all three species are semi-aquatic rodents), there are some characteristics, which allow the distinction of these species.
First, the three species clearly differ in their respective body size, the length of the tail, and the body mass of the adult animals:
83 - 102 cm
30 - 34 cm
19 - 30 kg
45 - 65 cm
30 - 45 cm
4 - 8 (max 12) kg
25 - 35 cm
20 - 25 cm
600 - 1800 g
source: Niethammer, J. & Krapp, F. (1978): Handbuch der Säugetiere Europas. Band 1. Rodentia I. - Akademische Verlagsgesellschaft, Wiesbaden.; Niethammer, J. & Krapp, F. (1982): Handbuch der Säugetiere Europas. Band 2/I. Rodentia II. - Akademische Verlagsgesellschaft, Wiesbaden.
Moreover, there are also differences in body shape and quality of the body hair, which are, however, sometimes difficult to perceive in living animals.
Structure of the tail
[To the top]
The most conspicuous, external feature is the structure of the beaver tail: it is (dorsoventrally) flattened to the form of a trowel. The 12 to 16 cm broad beaver trowel is hairless and equipped with scales. In contrast, the tail of the coypu is round in cross section, thinly haired and shows scales as well. The tail of the muskrat is laterally flattened (muskrats move their tail sideways when swimming and by this support the rowing motion of the feet). The tail of the muskrat is likewise almost hairless and covered with scales.
Structure of the fur
[To the top]
Contrastingly to the beaver and the muskrat, coypus possess long, conspicuously white vibrissae right and left of the nose and also the fur around the muzzle is often of a white colour. The fur of the muskrat on top is usually darker than the bottom side and the hair around the mouth is often of a lighter colour (yellowish-white to white) than at the rest of the body. In contrast, most beavers are of a uniform brown colour without conspicuous differences between the upper- and the underside.
Structure of the rear extremities
[To the top]
In the beaver, the large rear extremity is webbed. Also the rear extremities of the coypu are webbed, in contrast to the beaver the 5. toe is free (the web is missing between the 4. and the 5. toe). Contrastingly, the rear extremities of the muskrat are not webbed. In this species, the individual toes only show a lateral fringe of stiff swimming bristles (muskrats also use the tail to generate propulsion when swimming).
Body posture when swimming
[To the top]
The body posture during swimming is also different between the three species. In the muskrat, the back protrudes on its entire length almost evenly above the water surface and usually the lateral rowing movements of the tail are visible during swimming. In the coypu, the front of the body and the pelvis usually protrudes further above the waterline than the back between the front of the body and the pelvis. As a rule, also the white muzzle and the conspicuously white vibrissae are easy to recognise in the swimming animal. Finally, in the beaver only the head and the front of the body protrudes above the water surface when swimming, whereas the pelvis and the trowel are not to be seen. Occasionally, beavers dive in case of a supposed danger and loudly slap their tail on the water surface to alert other family members to the danger. This "tail-slapping" is comparably loud and characteristic for beavers.