Food processing by animals: do beavers leach tree bark to improve palatability?

Beavers store and consume tree parts in the bodies of water where they live. We examined whether such soaking renders food more palatable by leaching out undesirable compounds. In experiment 1, saplings of red maple, Acer rubrum (RM), were first soaked in a pond for periods of 2, 18, and 36 days, then offered to free-ranging beavers. Soaking for two days rendered RM slightly more acceptable to beavers. To further examine the time window around two days, RM sticks were soaked in distilled water in the laboratory for 1, 2, 4, and 6 days before presenting them to beavers (experiment 2). In experiment 3, twigs of three species were placed on land. Beavers placed RM in the water for 1 to 3 days before consuming the twigs. In experiment 4, sticks were provided in the water at Cranberry Lake Biological Station (CLBS). Most quaking aspen (QA) was consumed during the first night, and most witch hazel, Hamamelis virginiana (WH), during the third night. At Allegany State Park (ASP), no such difference was found. Twigs were provided in the water in experiment 5. At ASP, WH was taken after three days in the water, and at CLBS little WH was consumed, and only during the third night. A meta-analysis of all experiments shows that relatively more WH is consumed after two days than any other species. Experiment 6 traced the time beavers left their own harvested branches in the water. Unlike other tree species, WH remained in the water for two to four days before being consumed. Experiment 7 measured the phenolics leached into water from RM twigs and small pieces of bark soaked for 10 and 8 days, respectively. Shredded bark lost 50-60% of leachable phenolics into the water, and twigs 70-80%. We conclude that beavers can use water to leach undesirable compounds from their food. Although this effect was not robust, our study is the first of its kind.

Beaver response to recurrent alien scents: scent fence or scent match?

By repeatedly presenting an alien scent to territory-owning beavers, Castor canadensis, we tested two competing hypotheses about the function of scent marking: scent fence and scent matching. The scent-fence hypothesis predicts that territory owners should respond increasingly strongly over time towards a recurrent alien scent because of the ineffectiveness of previous responses. The scent-matching hypothesis predicts that the intensity of response should be the same or decrease because, without the presence of the intruding signaller coupled with the chemical signal, the presence of the scent itself does not advertise the ownership of a territory. The response level of resident beaver families was stable to strangers' anal gland secretions (AGSs) and decreased to strangers' castoreum during a period of 6 days. These results support the scent-matching hypothesis but not the scent-fence hypothesis. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

Neutral compounds from male castoreum of North American beaver,Castor canadensis.

North American beavers (Castor canadensis) mark their territories with castoreum, the strong-smelling paste in their castor sacs. In their own territories, beavers respond with scent marking to experimental scent marks that consist of strange castoreum (or selected components). In part, the unique odor of castoreum is due to large amounts of phenolic compounds and neutral compounds. Purified neutral compounds were analyzed by GC. GC-MS, and NMR; identities of the neutral compounds were confirmed by comparing the properties of authentic compounds with those of the isolated compounds. We identified 13 neutral compounds that had not been reported before for castoreum. Most of these are oxygen-containing monoterpenes. Of the nine neutral compounds reported by Lederer (1949), only three are confirmed in our analysis; the other six neutral compounds are either absent or are not volatile enough to be detected by our methods. Eight compounds-6-methyl-l-heptanol, 4,6-dimethyl-l-heptanol, isopinocamphone, pinocamphone, two linalool oxides, and their acetates-were synthesized for structure identification and bioassays.

Bioactivity of beaver castoreum constituents using principal components analysis.

North American beaver (Castor canadensis) were observed to sniff from the water and make land visits to some synthetic chemical components of castoreum placed on experimental scent mounds (ESM). In previous analysis, the elicitation (presence/absence), completeness, and/or strength (number, duration) of these key responses served as separate measures of biological activity. In this paper, we used principal components analysis (PCA) to combine linearly six related measures of observed response and one index of overnight visitation calculated over all trials. The first principal component accounted for a majority of the variation and allowed ranking of the samples based on their composite bioactivity. A second PCA, based only on response trials (excluding trials with no responses), showed that responses to the synthetic samples, once elicited, did not vary greatly in completeness or strength. None of the samples evoked responses as complete or strong as the castoreum control. Castoreum also elicited more multiple land visits (repeated visits to the ESM by the same individual or by more than one family member) than the synthetic samples, indicating that an understanding of the castoreum chemosignal requires consideration of responses by the family unit, and not just the land visit by the initial responder.

Responses of beaver (Castor canadensis Kuhl) to predator chemicals.

Free-ranging beaver (Castor canadensis) in two different beaver populations in New York State were exposed to predator chemicals to test feeding inhibition. Solvent extracts of feces were applied to stem sections of aspen, the preferred food tree of beavers, permitting smelling and tasting the samples. Predator odors were from wolf (Canis lupus), coyote (Canis latrans), dog (Canis familiaris), black bear (Ursus americanus), river otter (Lutra canadensis), lynx (Lynx canadensis), and African lion (Panthera leo). The experiment was repeated. The predator odors reduced feeding compared to untreated or solvent-treated controls. One population consumed 17.0% of the samples with predator odor and 27.0% of the controls in summer, and 48.4% and 60.0%, respectively, in autumn. The other population accepted 3.15% of the predator odor samples and 11.05% of the controls in summer. Coyote, lynx, and river otter odors had the strongest effects. Diesel oil and bitter-tasting neem extract had weaker effects. Predator odors are promising as feeding repellents for beaver.

Beaver (Castor canadensis) responses to major phenolic and neutral compounds in castoreum.

North American beaver (Castor canadensis) mark their territories with castoreum, a chemically complex secretion from their castor sacs. The phenolic and neutral fractions of castoreum have been shown to elicit specific behavioral responses from beavers in a field setting. Our objective was to identify compounds/mixtures that evoked responses similar to those stimulated by castoreum. We assayed recently identified phenolic compounds, some phenolics that had been determined to be biologically active in previous studies, the neutral compound borneol, and combinations of phenolic compounds, neutral compounds, and the two combined. Biological activity was measured by the elicitation and extent of specific responses and their strength (duration, frequency, and proportion of beavers responding). Generally, single compounds stimulated fewer responses than mixtures. A 26-compound mixture of phenolic and neutral compounds elicited responses in a similar proportion of trials as castoreum. However, responses to castoreum were stronger than to any synthetic sample. Further investigation of different measures of response, namely, elicitation, completeness, and strength, are deemed necessary to fully decipher the design of social odors.

Red maple (Acer rubrum) inhibits feeding by beaver (Castor canadensis).

At many beaver (Castor canadensis) sites at Allegany State Park in New York State, red maple (Acer rubrum) is the only or one of the few tree species left standing at the ponds' edges. The relative palatability of red maple (RM) was studied in three ways. (1) At seven beaver sites, the available and utilized trees were recorded and an electivity index (E) computed. Of 15 tree species, RM ranked second or fourth lowest. (2) In experiment I, RM, sugar maple (A. saccharum, SM), and quaking aspen (Populus tremuloides) logs were presented cafeteria style at 10 colonies. RM was the least preferred. (3) Bark of RM was extracted with solvents. Aspen logs were painted (experiment II) or soaked (experiment III) with this RM extract and presented to beaver cafeteria-style, along with aspen and RM controls. This treatment rendered aspen logs less palatable, indicating that a chemical factor had been transferred.

Phenolic compounds from male castoreum of the North American beaver,Castor canadensis.

North American beaver (Castor canadensis) mark their territories with castoreum, the contents of their castor sacs. In their territories, beaver respond with scent marking to experimental scent marks consisting of castoreum, or selected single components. In part, the unique odor of castoreum is due to large amounts of phenolic compounds. Purified phenolic components were analyzed by GC, GC-MS, and NMR; identifications were confirmed by comparing the spectra of synthetic phenols with those of the isolated phenols. Of the 15 phenols reported elsewhere, only five were confirmed in our analysis; the other 10 phenolic compounds are either absent or are not volatile enough to be detected by our methods. In addition, 10 phenolic compounds have been identified in this study that were not reported in the previous papers concerning the constitution of castoreum.

Pheromonal activity of single castoreum constituents in beaver,Castor canadensis.

Behavioral activity of single components of beaver castoreum was demonstrated for the first time. In four experiments samples were presented to free-ranging beaver in their family territories. First, responses to whole castoreum and anal gland secretion (AGS) from males and females were tested. Second, 24 compounds, known to be constituents of beaver castoreum, were individually screened for activity. Four of these consistently released immediate responses during the observation periods. These are the phenols 4-ethylphenol and 1,2-dihydroxybenzene and the ketones acetophenone and 3-hydroxyacetophenone. In the most complete responses, the beaver sniffed from the water, were attracted to the odor, swam toward its source, went on land, and then approached, sniffed, pawed, and scent-marked the artificial scent mound. 4-Ethoxyphenol, a compound not yet found in castoreum, also released these responses. Five additional compounds resulted in a few delayed visits to the samples during the night following the observations, as evidenced by destroyed scent mounds. These are 4-methyl-1,2-dihydroxybenzene, 4-methoxyacetophenone, 5-methoxysalicylic acid, salicylaldehyde, and 3-hydroxybenzoic acid. Third, mixtures of 24 and six compounds were tested. Responses to these mixtures could be as strong as those to whole castoreum. Fourth, the four regularly active compounds were tested in two additional beaver populations and proved to be active there, too. The response was strongest in the densest beaver population.

Effects of predator fecal odors on feed selection by sheep and cattle.

The effectiveness of predator fecal odors in modifying feeding selection by sheep and cattle was investigated in two trials. In trial 1, animals could select from feed bins contaminated with coyote, fox, cougar, or bear fecal odor, and oil of wintergreen, or select the control feed. All odors were rejected (P<0.01) by sheep and cattle, except bear odors by sheep. In trial 2, animals could select feed during 10-min periods in an open 11-m × 16-m arena. Fecal odor did not influence approaches to feed bins, or head entries into bins. Only coyote fecal odor reduced (P<0.05) the time spent feeding in the contaminated bin, and increased (P<0.05) consumption from the control bin by both cattle and sheep. Some animals on some test days refused to feed from either feed bin, although cattle and sheep closely inspected bins. Results suggest that fecal odors may not prevent livestock from entering a treated area but may reduce the time spent grazing in such an area.

Experimental habitat scenting inhibits colonization by beaver,Castor canadensis.

Unoccupied beaver (Castor canadensis) sites in New York State were for two years experimentally scented with a mixture of beaver castoreum and anal gland secretion. These sites were colonized less often than unscented control sites. The beaver is the first mammal to have been shown experimentally to use intraspecific odor cues when settling in vacant habitat. Territorial pheromones may be useful as repellents for beaver or other rodents.

Responses of wild muskrats (Ondatra zibethicus L.) to scented traps.

Free-ranging muskrats were trapped in scented and blank traps in New York State at local ponds during all seasons and at a wildlife refuge in spring and early summer. In a total of 4839 trap-nights, 65 muskrats were caught. Trapping success was 1.34%. The overall responses to differently scented traps differed significantly. Adults preferentially entered blank and food-baited traps, whereas young showed no preference to blank, musk, or control odor. It appears that adults actively avoid musk, especially during the months May through July.

Alert odor from skin gland in deer.

Black-tailed deer (Odocoileus hemionus columbianus) discharge an odor from the metatarsal (MT) gland, located on the hindleg, when disturbed or alarmed. Freely moving, captive deer were exposed to the MT odor by means of a remote-release apparatus. Responses by males and females to MT odor from both sexes were recorded with a coding system and a video camera. When the odor was present, females became more alert and left the site more often than in the presence of control odors, odorless air, or deer urine. It is concluded that the MT secretion provides an alert signal, placing the odor into the class of alarm pheromones. There is no evidence that the closely related white-tailed deer,O. virginianus, possesses this alert (or alarm) odor system to the same degree.

Urine fractions that release flehmen in black-tailed deer,Odocoileus hemionus columbianus.

Flehmen (or "lipcurl") is a response of male mammals primarily to female urine, performed primarily during the reproductive season. To elucidate the components of female urine that release the Flehmen, urine of black-tailed deer (Odocoileus hemionus columbianus) was fractionated, and the fractions were presented to captive male conspecifics during three rutting seasons. The active principle (one or more compounds) is watersoluble, of low volatility, not readily extractable with organic solvents, and between 200 and 12,000 daltons in molecular weight. Several urine components were identified, but none of these showed activity.

Play behavior: persistence, decrease, and energetic compensation during food shortage in deer fawns.

White-tailed deer fawns continued to play despite an experimentally induced 33 percent milk shortage. They reduced play by 35 percent and general activity by 9 percent but increased grazing by 62 percent, resulting in virtually complete energetic compensation. This demonstrates the importance of play behavior in a mammal's activity budget.

Mammalian pheromone: identification of active component in the subauricular scent of the male pronghorn.

Male pronghorn (Antilocapra americana) mark vegetation by rubbing with their subauricular glands. Males respond to scent marks by sniffing, licking, thrashing, and marking. Hand-raised males were confronted with artificial scent marks consisting of whole extract of the subauricular gland or synthesized compounds corresponding to those identified from the extract. Of these, isovaleric acid released the strongest responses.