Mammalian Scent Marking

1. What they did

Since Hediger’s classic 1949 paper, scent marking by mammals has often been called “territorial marking”, as if marks mainly show which area an animal will defend. The author questions that idea. Field studies had already found that the black rhinoceros is not territorial and that chamois marking is not tied to holding a territory.

She reviews experimental studies of scent marking in captive mammals, mainly sugar gliders, rabbits, golden hamsters, Mongolian gerbils and marmosets, and adds results from her own study of nine captive Maxwell’s duikers at the Bronx Zoological Park. She looks at:

• Marking and dominance: do high-ranking animals mark more?
• Marking and strangers: do animals mark more after meeting, or smelling, unfamiliar members of their own species?
• The motivation of marking: is marking linked to aggression?
• The effects of marking on other animals.
• Marking with more than one source of scent at the same time.

2. What they found

Marking and dominance

• Sugar gliders live in groups of up to six adults with their young. The one or two dominant males do almost all of the marking, of both group members and the territory. Females rarely mark.
• In rabbits, dominant males and females mark more with their chin glands than subordinates do (in one enclosure, dominant males marked 8 times in an hour and subordinate males not at all). Dominant males also have much larger chin and anal glands than expected from their body weight. Dominant rabbits pile their marked feces at prominent places in their territory, and these feces smell more strongly, even to humans.
• After a fight between two male golden hamsters, the winner always marked more in the loser’s cage than the loser did in the winner’s (for example 20.6 versus 5.2 marks per 10 minutes).
• Male gerbils that marked most tended to win encounters. Dominant marmosets of both sexes mark more than subordinates.
• In the author’s duikers, males marked objects most, “type A” females (the female in each group that marked and groomed with the male most) about half as often, and “type B” females hardly ever. In a large enclosure, the dominant male marked most and the lowest-ranking male least.
• Dominant pangolins and chamois also mark more (dominant chamois marked 82 times, subordinates 35).

Marking and strangers

• Many species mark more after meeting strangers of their own species, especially of the same sex, but not after meeting members of their own group.
• A dominant male sugar glider marks more after smelling scent from a male of another group, but not scent from a female, from his own group, or from himself. Sniffing tests showed males can tell apart scent from different males and from different body parts of the same male.
• Male hamsters mark a lot in another hamster’s empty cage but little in their own or a clean cage. In a female’s cage they mark least on the day she is in estrus (in heat) and the day after.
• A dominant male marmoset’s marking rose from about 5 to 17 marks per hour to about 43 to 55 after a strange male had been present. Dominant females increased more after a strange female.
• Male and type A female duikers increased their marking more after an extra animal of their own sex had been present.

Marking and aggression

• Frequent, vigorous marking happens when there is reason to think the animal is motivated to attack: when it holds a territory, is dominant, or meets a same-sex stranger.
• Many marking glands depend on androgens (male hormones), which also make animals more ready to fight.
• When two male duikers mark each other it is always the prelude to a fight, and the author never saw a fight without it. Duikers marking at a high rate also thrash the marked object with their horns and paw the ground.
• Similar displays: roe deer mark branches with a forehead gland, thrash them with their antlers and scrape the ground; reindeer, elk and black-tailed deer combine urine marking, thrashing shrubs and pawing; the black rhinoceros urinates on a plant, smashes it with the horn and scrapes the ground with the hind legs. Ring-tailed lemur males hold “stink-fights” that can last from 10 minutes to an hour. Coatis mark with urine while threatening each other.

Effects of marking

There is little experimental evidence. Marks may act as threats (as suggested for marmosets). In sugar gliders, marking by the dominant male may hold back the development of other males, whose marking rises if he is removed. But an animal that marks a lot may keep its rank through its aggressiveness, not through the marking itself.

More than one source of scent

Sugar gliders, rabbits, gerbils and marmosets may mark with several glands, feces or urine in response to the same stimulus. Whether these carry different messages, or the same message in ways that work under different conditions (for example humid or dry), was unknown.

3. What they concluded

• Mammals mark frequently whenever they are both intolerant of and dominant to other members of their species. In other words, they mark when they are likely to attack, and likely to win if they do.
• This happens with territories, as Hediger pointed out, but also in other social systems, so marking should not be assumed to be territorial.
• Frequent, vigorous marking happens when the animal is probably motivated to aggression.
• How marks affect other animals is poorly understood, as is why many species mark with more than one source of scent.

6. Other technologies, skills or innovations

• Marking rates were counted in controlled tests: animals placed in another animal’s cage, in clean cages or in neutral areas, or given filter paper or cloth carrying scent from strangers.
• Sniffing time was used to test whether sugar gliders could tell scents apart: once they got used to a repeated scent, a longer sniff at a new scent showed they noticed the difference.