# Why do river otters scent-mark? An experimental test of several hypotheses

> What is a river otter saying when they leave spraint at a latrine? Researchers in Alaska offered wild-caught male otters a sniff of different spraints and found they cared most about the scent of other males, with dominant males the most curious of all. The results suggest otter latrines may work more like a social noticeboard for status than a “keep out” sign.

Summary by Kersey Lawrence, Original Wisdom. Updated 9 November 2026. Page: https://www.originalwisdom.com/tracking-literature/2004-rostain-ben-david-why-do-river-otters/

## Citation and access

- **Authors:** Régan R. Rostain, Merav Ben-David, Pamela Groves and Jan A. Randall
- **Year published:** 2004
- **Journal or source:** Animal Behaviour
- **Full citation:** Rostain, R. R., Ben-David, M., Groves, P. and Randall, J. A. 2004. Why do river otters scent-mark? An experimental test of several hypotheses. Animal Behaviour 68(4): 703–711.
- **DOI:** 10.1016/j.anbehav.2003.10.027
- **Access status:** Publisher link only
- **Where to find it:** https://doi.org/10.1016/j.anbehav.2003.10.027

## Tags

- **Species:** Mammals > North American river otter
- **Region:** North America > United States
- **Behaviour and ecology:** Behaviour; Communication
- **Methods and technology:** Direct observation; DNA; Linear regression; Mann–Whitney U test; Wilcoxon matched pairs test
- **Data type:** New field data
- **Observer qualification:** Not needed
- **Discipline:** Behaviour and ecology
- **Year published:** 2004

## Detailed keywords

- **Species:** Studied: North American river otter (Lontra canadensis), 15 wild-caught adult males held in captivity. Scent sources: spraints from 10 zoo otters (seven adult males, three adult females) and from the captive males; faeces from Steller sealions (Eumetopias jubatus; one male, two females) as the other-species scent. Discussed for comparison: Eurasian otter (Lutra lutra), European badger (Meles meles), stoat (Mustela erminea), ferret (Mustela furo), weasel (Mustela nivalis) and mink (Mustela vison).
- **Location and habitat:** Otters live-captured in western Prince William Sound, Alaska, United States (coastal, marine habitat), and held at the Alaska Sealife Center in Seward, Alaska, in a 90 m² enclosure with one large and four smaller salt-water pools. Spraints also came from Oakland Zoo (California), Washington Zoo (given as Oregon), Woodland Park Zoo (Washington) and Coyote Point Museum (California).
- **Topics:** scent marking; spraints (otter faeces) and latrine sites; olfactory communication; olfactory preference tests; species identity; reproductive status; territoriality; intragroup communication; social hierarchy and dominance; kin recognition and relatedness; overmarking; social behaviour (touching, grooming, social rubbing, food sharing, play, play wrestling, pawing, pushing, biting, fighting); captive study; spraint and latrine surveys for monitoring otter populations.
- **Statistics or models:** Wilcoxon paired-sample test; Friedman test for a randomized block design; Mann–Whitney U test (one-tailed); linear regression of relatedness against the difference in investigation time; dominance ranks from the Dominance Structure Applet using the Batchelder–Bershad–Simpson (BBS) method; relatedness coefficients (R) from nine microsatellite loci with the program Kinship 1.2, calculated across 110 otters (the 15 captive males plus 95 from a companion study). Inconsistencies in the paper: (1) the methods give 12 males for the male versus female test, but the result is reported with N = 11; (2) relatedness among the 15 males is given as ranging from −0.031 to 0.75, but Figure 2 shows one value near −0.1; (3) overmarking is reported “of 24 trials”, although the three tests together involved about 30 trials; (4) the discussion says the male versus female test was “outside the breeding season”, while the methods say all tests were done directly before the mating season; (5) the centre’s acronym is given as ALSC in the methods and ASLC in the acknowledgments.
- **Data type:** New field data (captive experiment with wild-caught animals). Otters captured spring 1998 and held May 1998 to March 1999; spraints collected November 1998 to February 1999; social behaviour observed 18 January to 7 February 1999 (70.5 hours); preference tests 8 to 20 February 1999.

## Synopsis

### 1. What they did

North American river otters visit and mark prominent spots on land, called latrines, with spraints (faeces), urine and anal gland secretions (“jellies”). Much is known about who marks, how often and where, but much less about what message the marks carry. The authors tested several possible functions of spraints with wild-caught otters held in captivity.

Fifteen adult male otters, live-captured in western Prince William Sound, Alaska, in spring 1998, were held at the Alaska Sealife Center in Seward until they were released back into the wild. In February 1999, just before the mating season, each male was led into a test area with two jars, each holding 5 g of thawed faeces under gauze so the otter could smell but not see it. For 5 minutes the researchers recorded, by video and a handheld computer, how long the otter sniffed the air, ground or jar near each sample, and whether they scent-marked. Tests were blind, jar positions were switched, and only faeces were collected, without urine or jellies.

They tested four ideas with three choices:

- Species identity: an unfamiliar male otter’s spraint versus Steller sealion faeces (7 males).

- Reproductive status: an unfamiliar adult male’s spraint versus an unfamiliar anoestrous (not in heat) adult female’s spraint (12 males).

- Territory or group membership: a familiar male’s spraint (one of the other captive otters) versus an unfamiliar male’s spraint (12 males).

- Social status and kinship: for the familiar versus unfamiliar test, they worked out whether each male ranked above or below the male whose spraint he was smelling, and how closely related the two were.

To rank the males, they watched social interactions for 70.5 hours over three weeks, at feeding times when all animals were active, and built a dominance hierarchy from friendly and aggressive interactions. Relatedness came from DNA in blood samples.

### 2. What they found

- Otter versus sealion: males spent more time investigating otter spraint (about 25 seconds on average) than sealion faeces (about 15 seconds).

- Male versus female: males spent more time investigating unfamiliar male spraint (about 13 seconds) than anoestrous female spraint (about 8 seconds).

- Familiar versus unfamiliar: males did not investigate unfamiliar spraints more or less than familiar ones.

- Dominance: six males were dominant and six subordinate to the male whose familiar spraint they were given. Dominant males spent more time than subordinates investigating both familiar and unfamiliar male spraint.

- Kinship: relatedness among the 15 males averaged 0.2, similar to wild otter groups in Prince William Sound. It had no link to how long a male investigated familiar versus unfamiliar spraint.

- Overmarking: the otters rarely marked over other otters’ spraints. They marked in 13 cases, but only three were within 1 m of the jars: once over a female spraint, once over an unfamiliar male’s and once over a familiar male’s.

- Social behaviour: aggressive interactions were rare: 82 of 1464 interactions, including three bites and one fight.

### 3. What they concluded

- Spraints probably signal species identity. The authors note that otters and sealions often meet when feeding on schooling fish in Prince William Sound, so paying attention to sealion scent would be useful to otters, and that tests with faeces of other members of the weasel family would explore this better.

- Communicating male social status seems to be a main function of spraints left at latrines. Dominant animals of other carnivores mark more and often mark over subordinates’ scent, so dominant otters may monitor others’ scent more closely. This may help keep social order without costly fights.

- They could not conclude that spraints mark territories, and found no evidence that spraints signal familiarity or kinship. Group membership in these coastal otters changes between seasons and years, and groups seem to form around cooperative fishing rather than kinship.

- They could not rule out that spraints signal reproductive condition, because the female spraints came from anoestrous females collected months earlier, and urine or anal gland secretions may carry that message instead.

- Suggested next steps: offer males spraints of oestrous and anoestrous females; repeat the tests with females; offer the familiar scents of a higher- and lower-ranking group member; and compare how often dominant and subordinate otters mark.

### 6. Other technologies, skills or innovations

- Newton Message Pad 2100 with Ethoscribe software for recording behaviour, plus a remote camera with a microwave link to the observation room and frame-by-frame video scoring.

- DNA microsatellite fingerprinting (nine loci) and the Kinship program to measure relatedness.

- The Dominance Structure Applet to rank the males from observed interactions.

### 7. Implications for conservation (from the paper)

- Spraints are commonly used to judge the status of otter populations. Because how often an otter leaves spraint is likely to vary with sex, rank and whether they live socially or alone, understanding what scent marks mean may help correct population estimates based on spraint and latrine surveys.

- All otter species are threatened or endangered in some part of their historical ranges, so understanding scent marking may improve their conservation.

### 8. Implications for tracking (Original Wisdom's observations)

_These are Original Wisdom's observations, not the authors'._

- For trackers reading otter latrines, the study suggests a latrine is less a boundary marker and more a social noticeboard, where status among males may matter more than who is a neighbour or relative. This was tested on captive males with faeces only, so it may not hold for females, urine or jellies, or wild animals.

- The authors’ point that marking rates may differ between individuals is a reminder that counts of spraints at latrines reflect behaviour as well as numbers of animals.

## Cite this summary

Lawrence, K. 2026. Summary of: Why do river otters scent-mark? An experimental test of several hypotheses (Rostain and Ben-David et al., 2004). Original Wisdom, Tracking Literature. https://www.originalwisdom.com/tracking-literature/2004-rostain-ben-david-why-do-river-otters/