The role of scent marking in the social communication of wild golden lion tamarins, Leontopithecus rosalia

1. What they did

Golden lion tamarins are small monkeys of Brazil’s Atlantic Forest that leave scent marks by rubbing glands on their chest (sternal glands) or around their genitals (circumgenital glands) on branches. The authors asked what this marking is for. They tested four ideas: that scent marks show group members where food is; that they signal rank within a group; that they defend a territory; and that they advertise an animal’s status to neighbouring groups.

From May 1998 to April 1999 they followed 34 wild tamarins in eight groups in Poço das Antas Biological Reserve, Brazil, on 125 days. In 15-minute watches of one animal at a time, they counted every scent mark and noted whether it was placed on a fruit tree (a species the tamarins feed on) or another tree. They recorded every meeting with a neighbouring group, and the group’s position every 20 minutes to map territories and the areas shared with neighbours. Each animal was classed as dominant (alpha) or subordinate from behaviours such as arch walking, displacing others at food, and guarding mates. Juveniles were left out because they marked very rarely (nine marks in the whole study).

2. What they found

• They recorded 1125 scent marks from 29 adults and subadults in 339.4 hours of watching. Most marking seemed to be done by dragging the body along a branch.
• On average, adults marked 2.3 times per hour: alpha males 4.1, alpha females 2.4, subordinate males 1.3 and subordinate females 1.1.
• Food: tamarins marked fruit trees more often than other trees, relative to time spent feeding and not feeding. Against the authors’ prediction, they marked more fruit trees in the wet season than the dry season. Groups also visited and fed in more fruit trees each day in the wet season.
• Rank within the group: on days without meetings with other groups, alpha males marked more than subordinate males. Alpha and subordinate females did not differ.
• Territory: groups did not mark more in areas shared with neighbours than in areas they used alone.
• Meetings with other groups: alpha females marked more during these meetings than on days without them, and more than subordinate females during meetings. Alpha males and subordinate males did not mark more during meetings, and did not differ from each other during meetings. There were too few data to test subordinate females.
• Subordinate females were often daughters (or granddaughters) of the alpha male: only two of the five groups with subordinate females had ones unrelated to him. Five of the six groups with subordinate males had males unrelated to the alpha female.

3. What they concluded

• Scent marking in golden lion tamarins has several functions, depending on the social and ecological setting.
• Marking fruit trees probably helps group members find food again. More marking in the wet season may be because the tamarins came across more unmarked fruit trees then, or because rain washes scent away faster.
• Males appear to use how often they mark to signal rank to other males in their own group. Alpha females do not, perhaps because subordinate females are usually the alpha male’s daughters and pose no threat to her.
• The study found no evidence that scent marking defends a territory.
• Alpha females appear to use scent marking during meetings with other groups to communicate with females in those groups, perhaps to discourage females from moving in, since a female can only join a group by replacing the breeding female.
• Future work could measure how much scent is left and for how long, the chemistry of the scents, and how other tamarins respond (sniffing and marking over).

6. Other technologies, skills or innovations

• Territory sizes and shared areas mapped from locations every 20 minutes, using the Adaptive Kernel method in ArcView 3.1 with the Animal Movement extension.