Above: A portrait of a Eurasian lynx, Europe’s largest felid (Photo by Miha Krofel)
Written by Miha Krofel and Max Allen
Animals live in an invisible world of scent that is often undetectable to humans. This is most apparent to many of us as we walk our dogs and watch as they interact with their world: it seems as if they are interpreting with the scent of other animals as we might read our morning newspaper. As biologists that study cryptic species, we often wonder about the aspects of animal’s lives that we cannot observe, including how animals communicate through scent marking. Among solitary carnivores, scent marking is often used to communicate with each other. It is used as a means of competition to advertise that a given territory is occupied and a way to select mates, but can also be affected by other species, including humans.
Human development, including roads and trails, is increasing worldwide, and is known to have many effects on wildlife. Many wildlife species avoid human activity and scent, which can alter their use of areas in space and time. Human activity and development also affects other animal behavior traits, including their movement, home range size and distribution, selection of breeding sites, and feeding behavior. Research has shown that some species may select for scent marking areas that are away from human development, but the effects that humans, including infrastructure, have on scent marking behavior of wild animals are not well understood.
To study the potential effects of human infrastructure, specifically forest roads, on the scent marking behavior of solitary felids, we followed tracks made in snow by Eurasian lynx. Eurasian lynx are a solitary apex carnivore that is found across Europe and Asia, and have large home ranges. They defend their home ranges from other lynx of the same sex, and scent mark (via urine spraying and rubbing with head and body against various objects) throughout their home range. This territorial behavior enables lynx to self-regulate their population density, which ensures sustainable use of their prey. In contrast other lynx species (Canadian lynx, bobcat and Iberian lynx), which are specialized for hunting hares, rabbits and other smaller mammals, the much larger Eurasian lynx occupies ecological niche of a large predator (similar to mountain lions in North America) and hunts large prey, such as roe and red deer, Alpine chamois and reindeer.
In general, lynx avoid areas of intensive human land use, but they regularly use forest roads and similar habitats that are used less frequently by humans. We conducted our study in the forested landscape of Slovenia’s Dinaric Mountain Range in Central Europe. Eurasian lynx in Slovenia are part of the Dinaric lynx population, one of the most threatened lynx populations in Europe. In this human-dominated landscape there is a dense network of regularly maintained human routes (primarily for logging activities), with an average density of approximately 2 km of gravel forest roads and 10 km of logging dirt tracks per km2 of forest.
We used intensive snow tracking to document the scent marking rates and behaviors of Eurasian lynx across six winters. We followed the Eurasian lynx tracks a total of 94 km and recorded 619 events of scent marking via urine spraying. Most (94%) of the lynx tracks alternated several times between human routes and natural habitat. Lynx walked in natural habitat (i.e. off-road) 58% of time, and 42% on human routes.
Tracking the lynx was pretty much as simple as it sounds. After a fresh snowfall we located a new lynx track and followed it while documenting the location of each occurrence of scent marking, using a handheld GPS to record the location of the scent mark as well as the course and length of the lynx path. We focused on urine spraying, because cheek and body rubbing was difficult to detect and claw marking was infrequent (n=2). When urine marking, lynx typically create an easily recognizable track pattern in the snow by making a short detour from their direction of travel and turning their hindquarters towards a vertical object in order to spray urine upon it. We also documented whether the sprayed urine occurred on a human route (i.e., gravel forest road or logging dirt track) or in natural habitat (i.e. off-road).
The typical scent marking sequence of a Eurasian lynx. First cheek rubbing, then spraying urine.
Tracking animals is one of our most enjoyed field biology pursuits, and gives incredible insights into an animal’s lives. In our early days as biologists we would spend each winter following the trails of animals. We would spend a winter tracking one species, with a focus on a given individual when possible, and would learn as much as we could about the species from tracking and reading whatever we could find. The technique is also non-invasive, but it is generally underutilized by modern wildlife biologists and there are few articles published these days that use tracking as a technique.
Our first goal in this study was to determine whether lynx scent mark more or less frequently on human routes compared to natural habitats. Compared to previous studies of scent marking rates of felids, the overall mean urine spraying rates we found for Eurasian lynx in this study (7.1 sprays/km) were the highest marking rates reported to date (with the exception of studies that only reported the maximum rates they found). The scent marking rates we recorded in natural habitats (5.8 sprays/km) were similar to previous studies of lynx and other felids, but marking rates we recorded on human routes (11.2 sprays/km) were over 3 times higher than other documented marking rates.
The scent marking rates (scent marks/km) from tracking studies of felids noted in the scientific literature.
|Rate (scent marks/km)|
|Species||All||Male||Female||Type of Marking||Source|
|Lynx lynx||7.10||9.09||1.10||Urine Spraying||This Study|
|Lynx lynx||5.83||7.38||0.52||Urine Spraying||This Study|
|Lynx lynx||11.19||14.00||3.59||Urine Spraying||This Study|
|Lynx lynx||1.35||1.81||0.94||Urine Spraying||Sæbø, 2007|
|Lynx lynx||3.40||n.a.||n.a.||Urine Spraying||Vogt et al., 2016|
|Lynx lynx||1.03||n.a.||n.a.||Urine Spraying||Hucht-Ciorga, 1988|
|Lynx lynx||0.02||n.a.||n.a.||Claw marking||This Study|
|Lynx canadensis||10.6-11.8*||n.a.||n.a.||Urine Spraying||Saunders, 1963|
|Lynx rufus||3.001||n.a.||n.a.||Urine Spraying||Bailey, 1974|
|Panthera pardus||0.12||0.13||0.09||Claw marking||Bothma and Le Riche, 1995|
|Panthera pardus||0.08||0.10||0.01||Urine Spraying||Bothma and Le Riche, 1995|
|Panthera pardus||0.06||0.07||0.04||Body Rubbing||Bothma and Le Riche, 1995|
|Panthera tigris||2.11||2.40||1.80||Urine Spraying||Smith et al., 1989|
|Panthera leo||n.a.||3.682||n.a.||Urine Spraying||Schaller, 1972|
|Felis nigripes||n.a.||n.a.||64.6*||Urine Spraying||Molteno et al., 1998|
*only maximum rates reported
1only 2 observations
2only 1 observation
Our second goal was to compare scent marking rates between male and female lynx. Male felids often have higher rates of scent marking than females, and we observed the same for Eurasian lynx: males sprayed urine significantly more frequently (9.1 sprays/km) than females (1.1 sprays/km). Both sexes exhibited an increased frequency of scent marking on human routes (male=14.0 sprays/km; female=3.6 sprays/km) when compared to natural habitats (male=7.4 sprays/km; female=0.5 sprays/km). The high overall marking rates we observed are primarily due to male lynx, which more frequently walked on human routes and also scent marked more frequently than females.
Besides providing a means of easier and faster travel, the linear human infrastructure could also increase the efficiency of scent marking. Animals often mark in the same areas repeatedly, including on regularly used trails, which help the scent marks to be located by other individuals. The frequent use of human routes concentrates and channelizes movement, especially in rugged landscapes such as the Dinaric Mountains, and this may provide structure for the locations of ‘chemical bulletin boards’ that are created through scent marking. If so, scent marking on human routes would increase the probability of the message in the scent mark being received by a conspecific. We like to think about these marking sites as a kind of facebook page, where lynx share information with other animals in the area and also find potential mates.
Given the fact that most of the landscapes in the modern world are now covered by road networks the scent marking behavior of species such as lynx that selectively use human routes for indirect communication may have been profoundly changed due to human-caused habitat modification over the course of centuries. However, roads and other linear human infrastructure can have strong negative effects on carnivores, including collisions with vehicles, habitat fragmentation, limiting dispersal and gene flow, as well as increasing the access of people to remote areas which might increase legal and illegal hunting. While our results suggest that human routes with low use by humans such as gravel forest roads might improve effectiveness of indirect communication in solitary felids, it remains to be seen whether this could have beneficial impacts on important traits at the population level, such as increased breeding success and stability of the social system, and whether these effects are large enough to counteract the negative effects of human routes and development.
A Eurasian lynx marking a forest cabin.
Our study area is a mix of high intensity road development, but low intensity of human use on the forest roads. This combination appears to have produced pronounced effects on felid marking behavior, with human development increasing the scent marking rates of lynx. There are few reported studies of scent marking rates for felids (see table above), and this highlights the need for future studies that focus on marking rates in different types of habitat and among types of scent marking other than urine spraying. Studies to determine scent marking rates are labor-intensive, but can provide information on the function and mechanisms of scent marking, and we encourage future studies of this kind, especially of species and marking behaviors for which marking rates are poorly known.
Because the Eurasian lynx in the Dinaric Mountains one of the most threatened lynx populations in Europe their conservation is very important to us. Our next phase of research is reintroducing lynx from the Carpathian Mountains to increase the genetic diversity of our population. Keep up to date with our research as we implement these reintroductions and continue to explore carnivore ecology and behavior. We thank our field technician Lan Hočevar, and our funding sources: the Slovenian Research Agency (grant no. P4-0059) and the European Union (project “DinaRis”).