The peculiarities of hyena hygiene

Hyena hygiene is pretty similar to what you would expect from any large carnivore. Hyenas get clean by licking themselves (or even better, by getting others to lick them), although, like domestic dogs, they jump all over the opportunity to roll in something gross they find on the ground.  So, while being clean isn’t always the highest priority for hyenas, it is not uncommon for us to find them cleaning themselves or others.

Despite its function, grooming behavior doesn’t always appear as hygienic to us humans as it does to the hyenas. Like seeing your pet dog thoroughly licking its anogenital region, observing hyenas during bath time is not always the most pleasant experience. CAMI, for example, decided to ruin our peaceful evening the other night be loudly grooming her phallus right outside of my car window. I have heard Kenna complain on multiple occasions that a cleanliness-obsessed cub cleaning its phallus ruined her attempts to record vocalizations from a neighboring adult.

CAMI gave came right up to the car to make sure we
could clearly see and hear her dedication to cleanliness. 

Despite their unsightliness, these behaviors are familiar to anyone who spends a considerable amount of time observing animals, and we don’t really bat an eye when we see them. We were, however, treated to a new variety of unusual grooming behavior the other night by EREM and ARBA, twins who currently each have pairs of cubs about the same age at the current Happy Zebra clan communal den. These two moms often arrive at the same time, and like good mothers, get right down to nursing and grooming their kids.

ARBA (left) and EREM (right), each dutifully
nursing and grooming one of their two cubs.
Wait, what exactly is EREM grooming?

While watching EREM and ARBA grooming their kids, we noticed them both take particular care to groom the anogenital region of their cubs. This didn’t seem particularly unusual to us, until we noticed that the cub would often distend its anal sac during this process. The cub’s mom would then thoroughly groom the anal sac, the area where the cub will eventually begin producing the scent marking substance called paste. Not only did we notice both EREM and ARBA doing this, but their cubs each took a turn so that both littermates got a thorough anal sac grooming from their moms.

Smaug distending his anal sac so EREM can
give it a thorough cleaning, while Puff anxiously awaits his turn. 

What is going on here? I don’t know, but I wonder whether this grooming behavior is purely hygienic or if grooming of the anal sac is an important part of the ontogeny of paste production. Paste is produced by microbiota that inhabit the hyena’s anal sac, so proper maintenance of the sac could be important to encourage the colonization of the bacteria that will eventually produce the individual’s scent. Alternatively, a cub’s mom may be directly inoculating her offspring’s anal sac with these bacteria from her mouth. While these explanations are purely speculative, there are others who know much more about paste production than I. If you are interested in learning about how hyenas host specific bacteria in their anal sac that produce their scent, check out research by Dr. Kevin R. Theis (https://kevinrtheis.wordpress.com/), who has discovered some very cool stuff about the complex symbiosis that underlies hyena olfactory communication.