Burgener, N et al. 2009. Does anal gland scent signal identity in the spotted hyaena? Animal Behaviour 77:707-715.

Spotted hyaenas deposit a fatty scent secretion from their anal scent gland creating a scent post. In a previous study, the authors claim to have demonstrated that the hyaenas produce a group-specific odor; in this paper they studied how these odors are produced and if spotted hyaenas are able to differentiate between individuals by odor. Members of a group of hyaenas scent-mark near communal dens. This process is known as pasting and is a form of substrate marking, a method of scent dissemination mentioned in lecture. Individuals inspect pastings and anoint themselves ventrally with scent. Pastings are long lasting scents, though they may be covered up by other pastings through overpasting (when the gland is protruded) or dry pasting (when the gland is not protruded). The authors note that many animals use vomeronasal organs for this sort of conspecific olfactory communication; hyaenas, like most other carnivores, utilize the main olfactory epithelium.

Researchers observed the behavior of adult females at scent posts and determined if individuals sniffed, overpasted, dry pasted, or anointed themselves with the scent. Anointing was likely if overpasting occurred. Pastings were collected and taken to a lab where they were analyzed using gas chromatography-mass spectrometry. Compounds were classified as fatty acids, esters, aldehydes, alcohols, hydrocarbons, or unknown substances, and according to volatility.

A variety of statistical techniques were used to analyze factors controlling scent production. Researchers detected 252 volatile compounds in 143 samples from 84 individuals. Scent marks from males and females were equally complex (81.1 compounds/male, 83.6 compounds/female). Complexity of high and low ranking females was the same and no link was found for relatedness or age. Scent profile did change over time. Within clans there was a significant difference in composition of scent profile of high-ranking and low-ranking females (p=0.011). Behavioral evidence indicated that there were a greater number of responses to pastings by high-ranking females and that overpasting and anointing rates increased significantly when the social status of the female who deposited a scent mark was high.

The authors believe the difference in the scents of high and low ranking females and the differential response to scent posts of higher-ranked females indicates that spotted hyaenas can recognize individuals’ odors. The scent is chemically complex, composed of a large number of volatile compounds, which may allow for a signature that is specific to individual hyaenas. Because scents change over time, it is uncertain whether individuals are able to detect scents of dominant individuals because of a signal inherent in odors generated by dominant individuals or whether individuals must learn dominant females’ scents as they change over time. Some compounds are present only in high-ranking females and some only in low-ranking females; this could reflect diet or a response due to stress levels, indicating that odors may be modulated by, and are therefore an indicator of, internal status, a feature of chemical signals discussed in class.

Considering the complexity of the secretions studied, with an average of more than 80 volatile compounds per pasting, this demonstrates the usefulness of olfactory tuning. It seems likely that high sensitivity possible with label-lined coding of olfactory receptors is needed for the precise identification of individuals by gland secretion alone.

Spotted hyaenas produce a group scent, which the authors believe is created when individuals anoint themselves with conspecifics’ scents. This behavior is similar to that of male greater spear-nosed bats, which mark females in their group with a specific odor. While marking in this case is self-applied by females from the scents of other females, the idea of marking all members of a group with a shared odor that is not their own, or entirely their own, is very similar. Another behavior discussed in class is that of the sac-winged bat which uses its sac wings to store a mixture of urine and gular secretions. This is similar to the behavior of spotted hyaenas, which use their coats as a canvas to mix anal gland secretions from a variety of individuals in a group.

We discussed in class that oilier scents, such as fatty acids, would be used for marking territories as they are generally more stable than other compounds while more volatile hydrocarbons are used for odors that may be more fleeting but need to travel a greater distance quickly. Spotted hyaenas produce fatty acids, hydrocarbons, and a large number of compounds with intermediate levels of volatility. We discussed previously how sounds with a wide range of frequencies may be used for ranging as higher frequencies attenuate faster over distance. The implications of this were not discussed in the paper, however one cannot help but wonder whether this broad range of compound volatilities might not indicate time since the scent was deposited, much like ranging with vocalizations.