The scent of your enemy is my friend? The acquisition of large carnivore scent by a smaller carnivore

1. What they did

Many mammals use scent marks to talk to their own kind, but very little is known about scent as a way of communicating between species. In California’s Santa Cruz Mountains, pumas (mountain lions) mark shared “community scrapes”, areas where they scrape the ground and leave scent, and other carnivores visit them too. The researchers noticed that gray foxes visiting these sites sometimes rubbed their cheek, jaw and neck on the puma’s scrape, and set out to find why.

• Finding the scrapes. They documented 299 puma community scrapes from 2008 to 2015, using a custom algorithm to find likely sites and then visiting each in the field to confirm it.
• Filming them. From 2011 to 2015 they set infrared motion-triggered video cameras at 26 separate community scrapes, recording 60-second clips. They logged every visit by gray foxes, pumas, bobcats and coyotes, and for foxes whether they sniffed, urine marked or cheek rubbed.
• Testing ideas. Was the fox leaving its own scent (to compete with other foxes or attract mates) or picking up puma scent (for mates, or to put off predators)? They compared what objects foxes rubbed on, how recently a fox or puma had visited, whether rubbing changed with the season, and how often each of the four carnivores visited the scrapes.

2. What they found

Fox behaviour at the scrapes

• Gray foxes cheek rubbed during 92 of 903 visits (10.2%). Each bout averaged about four back-and-forth movements over 11 seconds.
• Visits with cheek rubbing lasted longer (about 38 seconds against 15).
• Foxes always sniffed when they cheek rubbed (against 65% of other visits) and urine marked more often (72.5% against 34.4%).
• A typical sequence: the fox investigated the puma’s scrape, rubbed on it, then sometimes urinated on or near it.

What they rubbed on

• Puma scrapes 78 times, bare ground 12 times, a bobcat scrape once and a shrub once. Foxes chose puma scrapes far more than other objects, and far more than chance would predict.

Timing

• Cheek rubbing was more likely the more recently a puma had visited: on average 8 days after a puma’s visit, against 20.5 days for visits without rubbing.
• It was less likely when another fox had visited recently (13.4 days against 11.3).
• Neither fox visits nor cheek rubbing changed with the season.

Which carnivores came

• Over the study, cameras recorded 1188 puma visits, 903 gray fox visits, 446 bobcat visits and only 22 coyote visits. Coyotes and bobcats were less common at the scrapes than pumas; gray foxes were as common as pumas and visited about 38 times as often as coyotes.

3. What they concluded

• Gray foxes seem to rub on puma scrapes to pick up fresh puma scent, not to leave their own. The authors describe this as the first record of a species applying another species’ scent to themselves for their own benefit, and of a subordinate species using a dominant species’ scent to communicate with other species.
• Rubbing did not follow the breeding season and did not track recent fox visits, so mate attraction seems unlikely. Gray foxes pair up all year, though, and the sex of the foxes was unknown.
• Smelling like a puma might make a coyote or bobcat hesitate just long enough for the fox to escape up a tree, its main defence. Coyotes appeared to avoid the scrapes. The authors say this predator-avoidance idea is worth testing directly, ideally with tagged foxes.
• Some rubbing on “ground” may have been on puma scrapes the team had not recorded, as some of those spots looked like scrapes.
• Scent marking between species may be a rich area for research and could help shape where species live and how many there are.

4. How tracking was or was not used

The study rests on a puma sign: the scrape. Potential community scrapes were found with a custom algorithm and confirmed by field visits, but the paper does not describe how scrapes were recognised on the ground (it refers to Allen et al. 2014). The behaviour itself was recorded on video, not from tracks and signs. The authors note that some fox rubbing they recorded as “on the ground” was at spots that looked like puma scrapes.

5. Tracker or observer certification

Not reported. Nothing is said about who confirmed the scrapes in the field or scored the videos.

6. Other technologies, skills or innovations

• Motion-triggered infrared video cameras (Bushnell Trophy Cam) recording 60-second clips, which showed behaviour that still photos would miss.
• A custom algorithm to locate potential puma community scrapes.
• The paper is a “video article”, with clips of a puma scraping, a fox cheek rubbing, the full sniff, rub and urinate sequence, and a fox escaping a bobcat by climbing a tree.

7. Implications for conservation (from the paper)

• Scent marking between species may be a mechanism that affects the distribution and abundance of species, much as calls between species can.
• How species read and use each other’s scent is under-studied and needs more research to understand carnivore communities.