The plant physical features selected by wildcats as signal posts: an economic approach to fecal marking

1. What they did

European wildcats are solitary and territorial, and they rely on scent marks to communicate with one another, especially in the breeding season. Leaving scent marks has a cost, so the authors expected wildcats to place their scats where they would be found most easily. They asked whether wildcats choose particular plants to leave their scats on, and which features of the plants matter.

• Finding scats. From September 2008 to June 2009, they walked 32 transects of 300 m each month, spread along nine routes on roads (1 to 12 km long) in and around the Montes do Invernadeiro Natural Park in Northwest Spain. They looked for fresh wildcat scats on plants and ignored scats on other surfaces. A scat counted as fresh when it had a moist layer of mucus, a strong smell and no sign of drying out.
• Confirming who left them. Wildcat scats are hard to tell apart from those of feral cats and hybrids, so 41 scat samples from across the area were tested with DNA to confirm the species, identify individuals and find their sex.
• Measuring the plants. For each marked plant they recorded the species, the maximum height and diameter, and whether it was visually conspicuous: the plant that stood out most within a circle of 2 m radius, judged from a wildcat’s eye height. A plant marked again was not counted twice.
• Measuring what was available. In 196 plots (1 by 3 m) along the same roads, they measured the four largest plants in each plot in the same way.
• Comparing. They compared marked and unmarked plants with statistical models and tests of use versus availability.

2. What they found

Who left the scats

• DNA was readable in 26 of the 41 samples (63.4%). All 26 were from wildcats; none came from other carnivores, and the samples were genetically different from domestic cats.
• The scats came from at least 16 individuals: five males and 11 females.

Which plants they chose

• They found 104 fresh wildcat scats on plants and compared these plants with 519 unmarked plants.
• Diameter mattered most. Marked plants were wider than unmarked ones. Wildcats marked plants over 26 cm across, even though plants 6 to 20 cm across were the most common.
• Height did not matter. Marked plants averaged 39.5 cm tall, much like the plants available. Scats sat on average 10.3 cm above the ground.
• Standing out mattered. 77.9% of scats were on visually conspicuous plants, although only about half the available plants (49.1%) were conspicuous.
• Plant type mattered. 66.3% of scats were on herbaceous plants (false brome), 22.2% on woody plants and 11.5% on the “pulse” grasses. The grasses tall oatgrass, quacking grass and Yorkshire fog were clearly avoided (Jacobs’ index -0.74).
• False brome, bell heather, prickled broom, broom, blackberry and yellow rock rose were marked more often than expected from how common they were.

3. What they concluded

• Wildcats do not leave their scats on plants at random. They choose wide, conspicuous plants of certain types, which likely makes the marks easier for rival wildcats and potential mates to find. This fits the “economic” idea that animals place scent marks where they are most likely to be detected.
• Wider plants may also hold the scat better, so it does not fall to the ground and stays detectable for longer. Woody plants with rough, evergreen leaves may help the signal last; sparse grasses leave the mark exposed to the weather.
• False brome, the plant most often marked, has many broad leaves that hold scats. Bromes also appear often in the wildcats’ diet in this area, so the authors suggest the cats may be marking an important resource.
• Conspicuous marked plants may also act as visual and scent landmarks that help wildcats find their way, especially at night, but more study is needed.

4. How tracking was or was not used

The study is built on finding and identifying scats. Observers walked transects along roads looking for fresh wildcat scats on plants, judged freshness from moisture, smell and drying, and recorded the plant each scat was on. Scat identification was checked with DNA on 41 of the scats. No trailing was reported.

5. Tracker or observer certification

Not reported. The paper does not say who searched for and identified the scats, or how experienced they were. The authors note that wildcat scats are hard to tell from those of feral cats and hybrids by shape and size; DNA confirmed wildcat for all 26 samples that could be read, but 15 of the 41 samples gave no result, and the paper does not say how the other scats were confirmed as wildcat.

6. Other technologies, skills or innovations

• DNA from scats: species identification from a short nuclear gene fragment, individual identification from 12 microsatellite markers, and sex identification with a gender-specific marker.
• A simple field measure of visual conspicuousness: is the plant the most obvious one within 2 m, viewed from a wildcat’s height?

7. Implications for conservation (from the paper)

• Clearing roadside vegetation may remove wildcats’ preferred marking sites and their scent marks, which could change their marking behaviour and orientation and affect how they space themselves.