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THE CANADIAN FIELD-NATURALISTVol. 112Free-ranging Eurasian Beavers, Castor fiber, Deposit Anal GlandSecretion when Scent Marking Telemark College, Department of Environmental Sciences, N-3800 B0, Norway Rosell, Frank, and Frode Bergan. 1998. Free-ranging Eurasian Beavers, Castor fiber, deposit anal gland secretion whei scent marking. Canadian Field-Naturalist 112(3): 532-535.
Two adult free-ranging Eurasian Beavers {Castor fiber) were observed depositing anal gland secretion at the border of theiterritory by everting the "cloaca", protruding the anal gland openings and rubbing them against the surface as the animawalked over the scent mound. We suggest that anal gland secretion applied to scent marks on land has some as yeunknown function in territory defense of the Eurasian Beaver.
Key Words: Eurasian Beaver, Castor fiber, scent marking, anal gland secretion, Norway.
Scent marking apparently plays an important role in territory defense of both the Eurasian Beaver (Castor fiber) (Nolet and Rosell 1994; Rosell and Nolet 1997; Rosell et al. 1998) and the NorthAmerican Beaver (C. canadensis) (Houlihan 1989; Welsh and Muller-Schwarze 1989). Scent is usuallysecreted onto small piles of mud and debris close to the water's edge (Wilsson 1971; Rosell and Nolet1997). All age classes and both sexes mark within the territory (Wilsson 1971; Buech 1995). Scent marksare assumed to signal occupancy to potential intruders, notably dispersing subadults (Svendsen 1980;Rosell and Nolet 1997; Rosell et al. 1998), and are deposited in greatest concentrations at territorial bordersduring the entire year (Rosell et al. 1998).
Both Eurasian and North American beavers possess a pair of anal glands and a pair of castor sacs located in two cavities between the pelvis and the base of the tail (Walro and Svendsen 1982; Valeu1988). Both seem to be involved in chemical signal ing. The anal gland is a holocrine secretory gland butthe castor sac is only a pocket lined with a laye of nonsecretory epithelium. Both open into the uro genitalpouch (cloaca). Anal glands are under seem ingly more muscular control than are castor sac (Svendsen1978). Beavers deposit copious amount of castoreum on scent mounds apparently by flush ing castoreumout with the urine (Svendsen 1978; Castoreum is deposited on the scent mound withou the animal actuallymaking contact between the bod and the substrate. In contrast, anal gland papilla must be "rubbed" on thesubstrate in order to depos: exudate from the anal gland (Wilss on 1971 Svendsen 1978).
It is at present uncertain whether or not anal glan secretion (AGS) is used in scent marking by beaver; Sun and Miiller-Schwarze (1997) report that North American Beavers actively deposit castoreum whilemarking, but how the AGS is deposited needs to be clarified. Schulte et al. (1994) report that beavermounds are marked with urine and castoreum from castor sacs, and possibly with AGS. Tang et al. (1995)report that beavers deposit castoreum and AGS, and Tang et al. (1993) report that beavers applycastoreum to scent mounds, but mention nothing about AGS. On the other hand, Wilsson (1971) andOwesen (1979) observed captive Eurasian Beavers depositing AGS when scent marking. Hodgdon(1978) also noted that free-ranging North American beavers deposited AGS on scent mounds. Recently,several authors have studied the response of beavers to artificial scent mounds (Miiller -Schwarze andHoulihan 1991; Schulte 1993; Sun 1996), but none observed that resident beavers responded bydepositing AGS (L. Sun, personal communication; D. Miiller-Schwarze, personal communication). The aimof this study was to monitor Eurasian Beavers depositing AGS at their territory border where markingactivity was known to be intense.
On 21 July 1997, we were stationed at the border between two territories with high scent marking activit y in t he B0 Ri ver (59°25'N, 0 9°03 'E), Telemark County, Norway. At this northerly latitude,light conditions during summer allow filming throughout most of the night. The animal livingdownstream belonged to territory 4 (hereafter animal 4) and the animal upstream to territory 3 (hereafteranimal 3). The animals were of unknown sex and estimated age for both was > 2 years. We videotapedthe movements of the beavers from the opposite bank (30 m) from 2145 to 2225 hours and later analyzedbehavior from the tape.
Both animals were observed depositing AGS at their common border by everting the "cloaca", protruding the anal gland openings and rubbing them against the surface as the animals walked over their scentmounds. When scent marking, the beavers held their tails rigid and almost horizontal just above the ground,afterwards dragging the tail over the scent mound. Once, a beaver sat on the mound during marking, afterfirst having protruded the anal gland. The beavers were never in a hurry to leave the marking site followingthe deposition of AGS.
Beaver 4 scent marked five times with AGS at four different sites. It was also seen scent-marking on seven other occasions but we were not able to determine if AGS was deposited. Beaver 3 was observedscent marking once with AGS, at the same site marked a few minutes earlier with AGS by the first beaver.
On two other occasions, it was impossible to determine if beaver 3 scent marked with AGS. After beaver 3 had over-marked the mound previousl y marked b y its neighbor, the first beaver promptly returned tomark the same site two more times. Both times it sniffed intensely at the mound before over-marking. Once,after the first over-marking, both beavers tail-slapped while only 15 m apart.
Our observations are apparently the first of free-ranging Eurasian Beavers depositing AGS when scent marking. Hodgdon (1978) never observed North American Beavers sitting on the mound during marking.
He reported that animals characteristically galloped or rushed to water and entered as soon as the body wasaway from the mound, though occasionally they would move away and feed. However, Eurasian Beaversnever rapidly departured from the scent marking site (Wilsson 1971; this study). Hodgdon (1978)observed that North American Beavers held the tail rigid, horizontal and elevated above the ground,without dragging over the mound following scent marking as we observed.
Other field observations (Rosell et al., unpublished) indicate that the beaver under certain circumstances use castoreum or AGS, or both. The odor of scent marks, as detected by humans, varies greatly within a site(Rosell et al. unpublished; B. Schulte, personal communication). Whether this is due to different beavers ordifferent scents (castoreum and AGS differ in smell), or a change in the nature of the site over a short-time period, is uncertain (B. Schulte, personal communication). On the basis of both visual and olfactorycues, Bergan (1996) suggested that castoreum was secreted far more frequently than AGS, particularly inwinter.
The AGS of the Eurasian and the North Ame r i ca n B e a ve r i s se x u a ll y d i m or p h i c (Gr0nneberg and Lie 1984; Sun 1996; Rosell et al. 1997), and the color and viscosity of AGS can be used for sexingboth beaver species (Gr0nneberg and Lie 1984; Owesen 1979; Valeur 1988; Schulte et al. 1995). Weassume that in areas where the two species occur together (see Nolet and Rosell 1998), AGS deposited onscent mounds is very important for species recognition.
The North American Beaver has also recently been shown to use the AGS to discriminate between unfamiliar sibling and unfamiliar non-relatives (Sun and Miiller-Schwarze 1997), and Schulte (1998)found that North American Beavers discriminated among castor-fluid scents from family, neighbour, andnonneighbour adult males. Therefore, information about kinship is probably contained both in AGS andcastoreum. However, field tests including both AGS and castoreum still need to be carried out to determine ifthe Eurasian Beaver also can discriminate among scents from family, neighbour, and non-neighbourindividuals. However, our observations may suggest they do. Both AGS and castoreum from a strangeconspecific can elicit territorial responses (Hodgdon 1978; Walro 1980; Welsh and Miiller-Schwarze 1989).
One major difference between the two marking organs of beaver may be important for the function of scent marking behavior. Castoreum has a low molecular weight (volatile) and AGS has a highermolecular weight (Gr0nneberg 1978; Gr0nneberg and Lie 1984; Tang et al. 1993, 1995; Sun 1996). Thismay indicate that castoreum informs intruders about territory occupancy at a distance, while AGS works atclose range. Indeed, most of the lipids in the AGS are of molecular weight above 300 and will thusnormally not be volatile enough to act as "chemical messenger" through the air (Gr0nneberg and Lie1984).
AGS seems to have many different functions. Information about kinship is coded in the AGS, and scent from anal glands differ between the sexes and also between the two species. So far, most researchershave given castoreum most attention when studying scent marking behavior. However, our findingsindicate that the function of AGS in territory defense should be examined more closely. We suggest that AGSapplied to scent marks on land has some as yet unknown function in territory defense of the Eurasian Beaver.
Acknowledgments
We thank H. Parker and L. Sun for reviewing our manuscript.
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