Brown Bears Use Anal Sac Secretions to Sniff Out Mates

Brown bears (Ursus arctos) sense their world largely through their nose (Figure 1). They have an extremely well developed sense of smell; under ideal conditions, they can detect odors from over a mile away. They often amble along with their nose to the ground, picking up scents of potential food sources or scents deposited by other bears.

Don_DeBold
Figure 1. A pair of brown bears (Ursus arctos), also know as grizzly bears, in Yellowstone National Park. (From Don DeBolt/Flickr)

Many other members of the Order Carnivora rely on scents to mark territories, recognize kin, or determine the reproductive condition of potential mates. These scents are produced by glands adjacent to the anus (i.e. anal glands) in some species of felids (cats), mustelids, and hyenas, Among bears, however, only the giant panda (
Ailuropoda melanoleuca) is known to have anal glands.

Brown bears (aka grizzly bears) range over vast areas and appear to recognize the scents of conspecifics, but do they have anal glands capable of producing secretions similar to those in the giant panda?

A group of Norwegian biologist working in Sweden (
Rosell et al., 2011) immobilized 17 wild brown bears and collected anal gland secretions for chemical analysis. The anal gland secretions were later analyzed by gas chromatography.

Their results (
Rosell et al., 2011) reveal that brown bears do have paired anal glands with ducts that open adjacent to the anus. The secretions from these glands were described as black or gray in color and highly odiferous. The secretions from male bears were significantly darker than those from females. Rosell and colleagues (2011) identified 90 compounds in the anal gland secretions, most of which were fatty acids, steroids, or hydrocarbons of one kind or another.

Male brown bears produced an average of 74 different compounds, while females produced a mean of 59 compounds. However, these differences between males and females were not significant. Interestingly, the relative abundance of these compounds differed between the sexes. Females produced more of four distinct compounds than males (Figure 2).

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Figure 2. The relative abundance of five compounds from brown bear anal gland secretions of males (solid) and females (hatched). (From Rosell et al., 2011)

The researchers conclude that brown bears have anal glands, and that their secretions may encode information about the sex of the producer. The volume of anal gland secretions tapered off as the breeding season progressed, suggesting that these scents may provide cues for finding mates over vast areas. In addition, the majority of compounds were large molecules (e.g. over 300 MW), suggesting that they would dissipate more slowly than smaller, more volatile compounds, making these compounds excellent long lasting scents.


References

F. Rosell, S. M. Jojola, K. Ingdal, B. A. Lassen, J. E. Swenson, J. M. Arnemo & A. Zedrosser (2011). Brown bears possess anal sacs and secretions may code for sex Journal of Zoology, 283, 143-152