Scent marking in wild banded mongooses: 1. Sex-specific scents and overmarking

1. What they did

Many mammals leave scent marks, and many place their own mark directly on top of another animal’s mark. This is called overmarking. It is common, but most of what is known about it comes from captive animals. The authors studied overmarking in wild banded mongooses, which live in large mixed-sex groups (8 to 70 animals) with several breeding males and females and no single dominant pair. Competition for mates happens mainly inside the group, because outsiders almost never join.

• The study population. Nine habituated groups on and around Mweya Peninsula, Queen Elizabeth National Park, Uganda, December 2005 to November 2007. Every mongoose could be recognised by a hair-clip pattern or a coloured collar, and one animal in each group carried a radio collar so the group could be found. Animals were trapped, briefly anaesthetised, tattooed and marked.
• Scent chemistry. While the animals were anaesthetised, the team collected anal gland secretions from 80 adults (40 males, 40 females) and analysed their chemical make-up in a laboratory in Switzerland.
• Watching marking in the wild. Banded mongooses mark in five ways: anal marks (dragging the anal region over a surface), cheek marks (rubbing the side of the face), token urination (a stamping of the hind legs while urinating), ordinary urination, and small amounts of scat left at latrines. Each time a mongoose marked a spot, the observers gave that spot a number (a “scent station”), noted who marked it, with what, and on what surface, and then recorded in order every animal that sniffed or licked it and whether they overmarked it, until the group moved on. Each scent station was located with a handheld Global Positioning System (GPS) unit and placed on home range maps as either a shared (overlap) area or an area used by that group alone.
• Analysis. They asked what made an animal more likely to overmark a scent it had investigated: its own sex and age, the sex of the animal whose mark it was, the type of mark, and, where two marks were already stacked, which one was on top. Adults (365 days and older) and juveniles (up to 290 days) were analysed separately.

2. What they found

Scent chemistry

• The anal gland secretions of males and females were chemically different. 73 of 80 samples (91.3%) were assigned to the correct sex, against 50% expected by chance.

Overmarking by adults

• Both males and females were much more likely to overmark scent from their own sex: males overmarked other males’ marks, and females overmarked other females’ marks.
• This held for anal marks, token urination, urine and scat. Cheek marks were too few to test.
• It was not because each sex used different spots: males and females started marking on the same kinds of surface. Most scat (over 90%) and most urine was left on the ground; anal marks were spread across ground, objects and shrubs.
• When two marks were already stacked, the sex of the top (most recent) mark mattered; the sex of the bottom (original) mark did not.
• Glandular marks (anal and cheek) were more likely to be overmarked than urine and scat.
• Females were more likely than males to overmark urine and token urine from the opposite sex; for the other scent types there was no difference.

Juveniles and age

• Juveniles also overmarked a lot, but they did not pick out same-sex scents. Only the type of mark affected whether they overmarked.
• The tendency to overmark same-sex scent rose with age during roughly the first 1.5 years of life, around sexual maturity. Among adults, age made no difference.

Where in the home range

• The authors report that same-sex overmarking happened in the same way in areas shared with neighbouring groups and in areas used by the group alone.

3. What they concluded

• Banded mongooses have sex-specific scents, and adults overmark the scents of their own sex within their own group. The authors say this has not been described within groups for any other species.
• This supports the idea that overmarking is part of competition within each sex. Because food and other resources are not used differently by males and females, and because same-sex overmarking appears around sexual maturity, the competition is likely to be for mates or mating opportunities.
• Among males, competition is intense because adult males outnumber adult females and females come into oestrus at the same time. Among females, competition for the best males may be increased by this synchronised oestrus and by the heavy pup care males give (each weaned pup is fed almost entirely by one male “escort”).
• Overmarking was the same across the whole home range, which fits a role inside the group rather than only in defending the territory against neighbours.
• Detailed studies of overmarking by wild animals are needed to check and build on laboratory findings. Two companion papers look at males and females separately, at individual signatures in scent, and at links with breeding success.

6. Other technologies, skills or innovations

• Habituated, individually recognisable animals (hair-clip patterns, coloured collars, tattoos), with one radio-collared animal per group, so every marking and investigating animal could be identified.
• Critical incident sampling: recording every marking event and every later visitor at each scent station, in order.
• Handheld Garmin GPS units to map scent stations, and home range maps (95% kernel) to class each station as shared or exclusive ground.
• Chemical fingerprinting of anal gland secretions by gas chromatography–mass spectrometry (GC-MS).