Does human infrastructure shape scent marking in a solitary felid?

1. What they did

Roads and trails now run through most landscapes and are known to change how animals move, feed and breed. Much less is known about how they affect scent marking, which is the main way solitary cats communicate with each other. The authors asked whether forest roads and logging trails change how often Eurasian lynx scent mark.

They worked in the Dinaric Mountains of Slovenia, where forests are criss-crossed by a dense network of gravel forest roads and dirt logging trails used mainly for logging. After fresh snowfall, they found a fresh lynx track and followed it, recording with a handheld Global Positioning System (GPS) unit the route of the lynx and every place where the lynx sprayed urine. For each spray they noted whether it was on a human route (gravel road or logging trail) or in natural habitat (off-road).

They followed 20 lynx tracks over six winters between 2005 and 2017, and analysed the 18 tracks longer than 1 km (13 males, 3 females, 2 of unknown sex). On five occasions they followed a track across several days. The sex of each lynx was found from DNA in scats, urine and hair collected on the trail (8 tracks), from a radio-collared lynx sexed at capture (1 track), or from the tracks themselves: footprint size and whether kitten tracks were present (7 tracks). Because individuals could not always be identified, the same lynx were likely followed more than once.

They focused on urine spraying because cheek rubbing was hard to detect, Eurasian lynx generally do not mark with scrapes or scats, and claw marking was rare. They also reviewed every study they could find that reported scent-marking rates in wild cats and compared these with their own results.

2. What they found

Where the lynx walked

• They followed lynx for 94.1 km and recorded 619 urine sprays.
• 58% of the distance (54.2 km) was in natural habitat and 42% (39.9 km) on human routes: 30.2 km on gravel forest roads and 9.7 km on logging trails.
• Almost all tracks (94%) switched several times between human routes and natural habitat.
• Males walked on human routes more than females: about 54% of their distance against 15% for females.

How often they marked

• Overall, lynx sprayed urine 7.1 times per km on average (range 0 to 20).
• They marked almost twice as often on human routes (11.2 sprays per km) as in natural habitat (5.8 sprays per km), a statistically significant difference.
• Males marked far more often than females: 9.1 against 1.1 sprays per km.
• Both sexes marked more on human routes (males 14.0 against 7.4; females 3.6 against 0.5 sprays per km), but the difference was only statistically significant for males. Only three female tracks were analysed.
• Claw marking was seen only twice (0.02 marks per km).

Compared with other studies

• The overall rate was the highest reported for any wild cat, apart from studies that gave only maximum rates (such as one female black-footed cat and Canada lynx).
• Marking rates in natural habitat were similar to earlier studies of lynx and other cats. Rates on human routes were more than three times as high as other recorded rates, which made the overall rate about twice that of any earlier study.

3. What they concluded

• Human routes channel lynx movement, so marks left on them are more likely to be found by another lynx. Forest roads and trails may therefore help territorial cats communicate more effectively.
• The high overall rates come mainly from males, which used human routes more and marked more. This fits other studies of cats and of Eurasian lynx, and is expected given that males have larger home ranges. Human routes did not mark home range boundaries in this area; lynx used them throughout their ranges, likely for easy travel and to patrol their territories.
• Roads and trails may also make marking more efficient. Lynx in Switzerland marked more when walking in a straight line, and in rugged country straight walking is much easier on a road.
• The combination of a dense network of routes with low human use may be where the effect on marking is strongest. Earlier studies were mostly in areas with fewer roads.
• Human objects such as cabins, fences and poles stand out and may also be used as marking posts; a video in the paper’s supplementary material shows a lynx marking a forest cabin.
• Because the study was done in winter, some tracking days likely fell in the breeding season, when both sexes mark more. This could affect comparisons with other studies.
• Eurasian lynx may have adapted their marking behaviour to living alongside people over thousands of years. Since roads now cover most landscapes, the marking behaviour of species that use them may have changed profoundly.
• Studies of marking rates take a lot of work but show how and why animals scent mark. The authors encourage more of them, especially for species and types of marking that are poorly known, and in different habitats.

4. How tracking was or was not used

Tracking was the main method. The researchers found fresh lynx tracks in snow and trailed them, in some cases over several days, mapping the whole route with GPS. They identified urine spraying from the trail: when spraying, a lynx typically makes a short detour from its line of travel and turns its hindquarters towards an object, leaving an easily recognised pattern in the snow. They noted whether each spray was on a road, a trail or off-road. Scats, urine and hair collected along the trail were used for DNA sexing, and for seven tracks the sex was judged from footprint size and whether kitten tracks were present. Claw marks were also recorded.

5. Tracker or observer certification

Not reported. The paper says only that “we” snow tracked the lynx; nothing is said about who did the tracking or their experience. The results depend on spotting every urine spray along the trail and on sexing seven tracks from footprint size and kitten tracks.

6. Other technologies, skills or innovations

• Handheld GPS to record the course and length of each lynx trail and the location of every urine spray.
• DNA analysis of scats, urine and hair from the trail (20 microsatellite loci and one sex-specific locus) to sex the lynx.
• A table that brings together published scent-marking rates for wild cats, by sex, type of marking, season and habitat.

7. Implications for conservation (from the paper)

• Roads and other linear infrastructure can harm carnivores: vehicle collisions, habitat fragmentation, limits to dispersal and gene flow, and easier access for people, which may increase legal and illegal hunting.
• Routes with low human use might improve communication between solitary cats. It remains to be seen whether this benefits breeding success or social stability, and whether any benefit is large enough to outweigh the harm done by roads and other development.
• More research is needed on how people affect scent marking by carnivores in human-dominated landscapes.