Behav Ecol Sociobiol (2017) 71:136
DOI 10.1007/s00265-017-2366-5

ORIGINAL ARTICLE

Where to leave a message? The selection and adaptive significanceof scent-marking sites for Eurasian lynx
Maximilian L. Allen 1 & Lan Hočevar 2 & Maarten de Groot 3 & Miha Krofel 2

Received: 21 December 2016 / Revised: 1 August 2017 / Accepted: 8 August 2017
# Springer-Verlag GmbH Germany 2017

Abstract
Scent marking is an important aspect of social organizationand intraspecific communication for many mammals, including solitary felids. By selecting specific micro-locations forscent marking, an individual may increase its success indefending its territory and finding mates. Few studies, however, have reported the selection of scent-marking objects andsites by wild felids. To improve our understanding of thisbehavior and its adaptive significance, we developed and tested a set of mutually non-exclusive hypotheses explaining selection of scent-marking objects by Eurasian lynx (Lynx lynx).
We used snow tracking to locate and determine the characteristics of objects lynx used and selected for urine spraying.
Lynx did not mark objects according to their availability but
selected juvenile conifers and often marked the surface thatMaximilian L. Allen and Miha Krofel contributed equally to themanuscript.
Communicated by K. E. Ruckstuhl
Electronic supplementary material The online version of this article(doi:10.1007/s00265-017-2366-5) contains supplementary material,
which is available to authorized users.
* Miha Krofel
miha.krofel@bf.uni-lj.si; miha.krofel@gmail.com
1

Department of Forest and Wildlife Ecology, University of Wisconsin,
1630 Linden Drive, Madison, WI 53706, USA2

Wildlife Ecology Research Group, Department of Forestry,
Biotechnical Faculty, University of Ljubljana, Večna pot 83,
SI-1000 Ljubljana, Slovenia

3

Department of Forest Protection, Slovenian Forestry Institute, Večna
pot 2, SI-1000 Ljubljana, Slovenia

was sheltered from the elements (Bpersistence hypothesis^).
Lynx also selected for objects similar in size to lynx and objects located on straight road sections and avoided the mostfrequently available object types. This selection may haveboth promoted detectability of the messages by the conspecifics (Bdetection hypothesis^) and reduced energy expenditure of marking (Baccessibility hypothesis^). Our study also
indicated trade-offs faced by lynx, as the preferred marking
objects were often not readily available. Therefore, suboptimal marking objects were sometimes used, most likely inorder to maintain the high scent-marking frequency needed
throughout their territory. We suggest that Eurasian lynx,
and possibly other solitary felids, developed scent-marking
behaviors that increase effectiveness and efficiency of theircommunication.
Significance statement
Scent marking is a form of communication that serves several
purposes and allows the signals of the sender to reach a receiver indirectly. Persistence and detectability of these signals
can have high adaptive value for solitary felids since the signals are essential for advertising territories for competitors andmates. Although both of these uses may depend on the microlocation where scent is deposited, the majority of studies havefocused only on the marking sites used by felids and not on
their availability or selection. By snow tracking Eurasian lynx,
we showed that scent-marking sites most often used are notnecessarily the same as the sites selected. We also provide
insights into possible adaptive features of felid scentmarking and the possible mechanisms behind the selectionof marking objects which likely serve to increase the effectiveness and efficiency of scent marking.
Keywords Eurasian lynx . Lynx lynx . Scent marking .
Selection . Urine spraying . Communication

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Introduction
Scent marking is an important aspect of social organization andthe primary form of communication for many mammals, including solitary felids (Bailey 1974; Smith et al. 1989;
Ghoddousi et al. 2008; Allen et al. 2016a). Scent marking is aform of communication that allows signals of the sender toindirectly reach a receiver (Gosling and Roberts 2001; Steiger
et al. 2011) and is usually long-lasting (Alberts 1992; Jackson
1996; Vogt et al. 2014). Scent marking in felids serves several
purposes (Vogt et al. 2014; Allen et al. 2016b), with the best
understood uses being marking territories (Bailey 1974;
Gosling and Roberts 2001) and advertising for mates (Mellen
1993; Vogt et al. 2014; Allen et al. 2015). Urine and feces arethought to be a relatively limited resource (Steiger et al. 2011),
whose inexpensive nature outweighs the relative inefficiency ofattempting to reach conspecifics indirectly through scent marking (Gosling 1990). An individual may therefore increase its
success in defending its territory and finding mates by choosing
scent-marking sites that have a high probability of being visitedby conspecifics (e.g., Gosling and Roberts 2001) and by choosing micro-locations or plants which will increase the persistenceof the organic volatile compounds in urine (Alberts 1992;
Jackson 1996; Soler et al. 2009). Solitary felids occupy large
home ranges, which they cannot constantly scent mark throughout. Therefore, they can be expected to focus on efficiency andpersistence of scent marks, because persistent scent needs to berefreshed less frequently, and considerable effort might otherwise be required to regularly visit all parts of their large homeranges to ensure constant advertisement of their land tenure.
The majority of studies on scent marking by solitary felids
focus on the form and function of scent marking (see review inAllen et al. 2016a), and relatively few have reported the use
and/or selection of scent-marking objects and sites. European
wildcats (Felis silvestris) choose plants that are visually conspicuous (e.g., large diameter and grouping of plants) and preferentially select certain plant species (Piñeiro and Barja 2012;
Ruiz-Olmo et al. 2013). Similarly, leopards (Panthera pardus)
select a particular acacia species over others for claw marking(Bothma and Le Riche 1995). However, Geoffroy’s cats
(Leopardus geoffroyi) vary in their selection of scent-marking
objects based on habitat type (Soler et al. 2009). Snow leopards(Panthera uncia) regularly use protected (over-hanging) andnortherly-oriented rocky surfaces, which is believed to enhance
the longevity of scent marks by sheltering them from weather
and other environmental factors (Ahlborn and Jackson 1986;
Jackson 1996). The low number of studies focused on selectionof scent-marking objects and sites (i.e., including information
on availability, not only use) limits our ability to understandcompeting factors in selection, including the relative importance of ensuring persistence of scent marks, using conspicuous
objects to promote detectability and the accessibility of objects
for scent marking to reduce energy expenditure. To improve

Behav Ecol Sociobiol (2017) 71:136

our understanding of object selection in scent marking by wild
felids, we studied the scent-marking behavior of Eurasian lynx
(Lynx lynx) from Dinaric population.
Eurasian lynx are solitary apex carnivores that occur acrossEurope and Asia in several isolated populations, many of which
are small and considered threatened (Kaczensky et al. 2013).
Eurasian lynx have large home ranges, typically measuring several hundred square kilometers and > 1000 km2 in the northern
populations (Linnell et al. 2001). Their social organization issimilar to other solitary felids, displaying intrasexual territoriality with limited overlap on the periphery and overlapping homeranges between the sexes (Schmidt et al. 1997; Breitenmoser
and Breitenmoser-Würsten 2008). Lynx are polygamous andmonoestrous with peak of mating in late winter (Kvam 1990;
Breitenmoser and Breitenmoser-Würsten 2008). During thebreeding period, extra-territorial excursions of males have beenrecorded, sometimes with successful mating within the neighbor’s territory (C. Breitenmoser-Würsten, unpublished results
reported in Vogt et al. 2014). Aggressive intraspecific interactions are rare and usually occur between males during breeding
season (Mattisson et al. 2013). The stability of land tenure system is believed to depend mainly on indirect communication,
especially scent marking, which also plays a role in mate selection (Breitenmoser and Breitenmoser-Würsten 2008).
The typical scent-marking sequence by male and female
lynx begins with olfaction, followed by cheek rubbing, andfinally the spraying of urine (Online Resources 1 and 2). Malelynx are more frequent visitors to scent-marking sites andscent mark more frequently than females (Vogt et al. 2014,2016; Krofel et al. 2017). Scent marking shows seasonal variation (Schmidt and Kowalczyk 2006; Vogt et al. 2016), with apeak during the late winter breeding season and the lowest
frequency during summer when breeding females are denningand raising young (Vogt et al. 2014). Studies have shown
differences in the objects scent marked by lynx, with
Schmidt and Kowalczyk (2006) most frequently finding
bridge railings, corners of sheds, fences, and tree trunks used
for cheek rubbing, while Vogt et al. (2016) most frequently
noted urine spraying on rocks and juvenile conifers. However,these studies were based only on objects used by the lynx,
without knowing the availability of these objects in the environment, and it remains unknown whether lynx actively selectcertain objects or use them according to their availability. It
also remains to be seen which characteristics are most important if the selection of scent-marking objects does occur. Suchknowledge is essential for designing further studies and developing effective monitoring programs, which often rely on
the use of hair snares or photo traps (Schmidt and Kowalczyk
2006; Zimmermann et al. 2013).
We used snow tracking across six winters over a period of
13 years to study Eurasian lynx scent marking in the Dinaric
Mountains, Slovenia. Our objectives were as follows: (1) todetermine the use and selection of objects for urine spraying

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and (2) to test which additional characteristics of the marked
objects lynx were selecting for when urine spraying in respect
to their assumed adaptive significance (Table 1). Based on previous studies on felid marking behavior (Ahlborn and Jackson
1986; Bothma and Le Riche 1995; Jackson 1996; Breitenmoser
and Breitenmoser-Würsten 2008; Piñeiro and Barja 2012;
Ruiz-Olmo et al. 2013; Vogt et al. 2014) and characteristics ofdifferent objects to retain smell (Alberts 1992; Nie et al. 2012),
we developed a set of predictions, which we summarized into
three mutually non-exclusive hypotheses (Table 2). According
to the first hypothesis, the lynx would select for objects andcharacteristics that increase the persistence of scent marks(Bpersistence hypothesis^). Alternatively, lynx might selectfor objects and micro-locations that increase the probability of
being detected by other lynx (Bdetection hypothesis^) or thosethat decrease the amount of energy needed to mark them
(Baccessibility hypothesis^).

Materials and methods
Study area
Our study was conducted in the Northern Dinaric Mountain
Range in Slovenia (45°25′–45°47′N, 14°15′–14°50′E), where
the altitudes range from 200 m to the peak of Mount Snežnik

Table 1 The variables, descriptions, and possible values of the documented objects scent marked during snow tracking of lynx. We provide reasoning
behind our predictions of what objects and characteristics would be selected by lynx in conjunction with our hypothesis presented in Table 2
Variable

Description

Possible values

Reasoning behind the prediction

Object typeType of the object used for marking

Rocks, juvenile conifers, tree stumps,
tree trunks, other vegetation

Height

The height of the object< 0.5 m, 0.5–1 m, 1–2 m, > 2 m

Slope

The direction the marked side of theobject is facing according to theslope of the surrounding (20 m)
terrain
The side of the road curvature
where the object is locatedUpwards, downwards, flat

To prolong longevity of the scent lynx would use
and select for vegetation, which has higher
surface-to-volume ratio and captures moreurine. Also, the probability of inspecting
object increases for more conspicuous(i.e., rarer) objects.
Larger objects are more visible and therefore
more visually conspicuous, and smaller
objects (< 0.5 m) are below the noselevel of potential receivers and level ofurinating; therefore they are less accessible
for marking and receiving the signal.
The objects surrounded by flat ground areeasier to access for marking and receiving
the message. Objects on flat ground arealso visually more conspicuous.
Objects on the outer curve of the road areon the other side of the road from where lynx
normally walk (pers. observation) andusing them would increase the energy
expenditure and lower the chances ofbeing detected.
Objects facing the northern directions(NW, N, NE) are more sheltered fromexposure to sun and other environmental
factors.
Detectability for lynx is higher for the sidesof the objects that are parallel to theirdirection of movement, while accessibility
for the sender is easier on sides parallel or
towards direction of departure from the object.

Road curvature

Inner side of the curve, outer sideof the curve, straight road

Direction

The cardinal/intercardinal
direction the marked side of
the object is facing

N, NE, E, SE, S, SW, W, NW

Orientation

The orientation the marked sideof the object is facing in respect
to the direction of lynx travel

Towards, away, or parallel to thedirection of departure

Mossa

Presence of moss

With or without moss

Tilta

Tilt of the rockVertical, over-hanging, sloping
backwardsa

For rocks only

Presence of moss increases the surface of theobject, captures more urine, and could
prolong longevity of the scent.
Over-hanging rocks and vertical rocks better
shelter scent from precipitation and are
more accessible to mark and receive signal
from close distances because lynx can step
closer to the rock face.

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Table 2 Predictions and results of the scent-marking objects and theircharacteristics selected or used by the Eurasian lynx in the Dinaric
Mountains, Slovenia, according to the three hypotheses separating
persistence, detection, and accessibility (see Table 1 for description of
Variablethe variables and reasoning behind the predictions). Selectedcharacteristics are given among the results unless stated otherwise. For
direction and orientation, we assumed that use reflects selection, giventhat most objects were possible to mark from several sides

Predictions according to the three hypotheses:

Results

Persistence

Detection

Accessibility

Object type
HeightSlope

Vegetation––

Object types with lower availability
Larger objects
Flat

Use according to the availability> 0.5 mFlat

Road curvature
Direction–
NW, N, NE

Straight road or inner curve–

Straight road or inner curve–

Juvenile conifers
0.5–1.0 m
Downwards facing rocks
avoided
Straight road
SW, E, W

Orientation
Moss
Tilt

–
With
Over-hanging or vertical

Parallel––

Parallel or away–
Over-hanging or vertical

ParallelWitha
Sloping rocks avoideda

Most frequent use, but not confirmed selection in respect to availability

at 1796 m. The climate is a mix of influences from the Alps,
the Mediterranean Sea, and the Pannonia Basin with averageannual temperature of 7 °C, ranging from an average monthly
maximum of 18 °C to an average monthly minimum of− 2 °C, and average annual precipitation of 1700 mm. The
area is covered with mixed temperate forests intermixed with
agricultural fields and small settlements. The limestone anddolomite geology of the area results in a rugged karstic relief
and abundant karstic structures, such as cliffs, dolines, caves,and rock shelters. Lynx in Slovenia (currently estimated to
10–20 adult animals) are part of the Dinaric lynx population,
one of the most threatened populations in Europe (Krofel and
Jerina 2016).
Field methods
We used intensive snow tracking to document scent marking
in Eurasian lynx. After a fresh snowfall that had continuous
ground coverage, we searched for a fresh lynx trail and thenfollowed it while documenting the location of each event ofurine spraying, cheek rubbing, and claw marking. We used ahandheld GPS to record the course and length of the lynx pathand the coordinates for each occurrence of scent marking.
When urine marking, lynx typically make a short detour fromtheir direction of travel and turn their hindquarters towards
visually conspicuous objects in order to spray urine, which
creates easily recognizable track pattern in the snow (Vogtet al. 2016; Krofel et al. 2017). We used this movement patternin combination with the visual or olfactory detection of urine
to confirm each urine-marking event and locate the exact location of the scent mark. We also occasionally noted cheekrubbing and claw marking by inspecting objects approachedby lynx for hair and/or claw marks. We noted the sex of thelynx when possible through genetic analyses from samples on
the trail (Sindičić et al. 2013), the tracking of radio-collaredindividuals of known sex (Krofel et al. 2013), or the presenceof kittens for females. Because it was not possible to always
identify the lynx, we could not determine the exact number ofdifferent individuals sampled, and the same individuals werelikely tracked multiple times during the study period. We assumed that a track belonged to the same individual if it occurred in the same area (taking into account lynx home rangesize), same time period (<7 years apart), and was of the samesex (when information of sex was available). We also took
into account known life histories of some individuals (e.g.,
detected mortalities). The minimum number of different individuals sampled was eight.
We focused predominantly on urine spraying because wefound cheek rubbing difficult to detect and Eurasian lynx generally do not use scrapes or feces for marking (Breitenmoser
and Breitenmoser-Würsten 2008). When urine spraying occurred, we documented the type of the object used for marking(rock, juvenile conifer, tree stump, tree trunk, other vegetation,snow heap, human object, or other) and the height of theobject. We also documented four variables of the microlocation on the object that was marked: curvature of the road(inner or outer side of the road curve, or straight road),
cardinal/intercardinal direction of the side of the object
marked, and orientation of the marked side of the object inrespect to the travel path and slope of the surrounding landscape (see Table 1 for details). In our last years of monitoring(the winters of 2015–2016 and 2016–2017) when urine
spraying occurred on rocks, we also noted whether the rockwas covered with moss or not and the tilt of the rock.
On a subsample of lynx tracks on the forest roads (5 tracks,
12,381 m in total), we recorded data on the objects available

Behav Ecol Sociobiol (2017) 71:136

for scent marking to compare the availability and use of objects for urine spraying. When walking on the forest roads,
lynx almost exclusively marked the objects located on thesides of the road and did not leave the roads. Therefore, whensampling for availability of objects, we only sampled objects
present on the side of roads. For each 10-m road section(n = 1238), we marked which potential marking objects wereavailable along the edge of the road and noted which objects
were marked by the lynx (n = 106). We used 10-m sections as
our sample because we found that lynx would frequently markat 20-m intervals on roads.
It was not possible to record the data blind because ourstudy involved focal wild animals in the field.
Statistical analyses
We used program R version 3.3.1 (R Core Team 2016) and thenlme package (Pinheiro et al. 2016) for all of our statisticalanalyses, and in each analysis, we considered P ≤ 0.05 to bestatistically significant. We first calculated summary statistics
for our data and then tested our series of predictions.
For all forthcoming analyses, we used generalized linear
mixed models (GLMMs) using a Gaussian error distribution.
In each model, the individual ID with the transect ID nested
within it was included as a random effect, and because thetransects were not of equal length, we used the log transformation of the transect length as an offset.
To determine if lynx marked certain types of objects more
often than others when spraying urine, we used the percentage
of each object type (human object, juvenile conifers, othervegetation, snow heap, rocks, tree stump, tree trunk) per transect as our independent variable. First, the model was checkedwith snow heaps (the least used object type) as a control.
Then, the model was repeated with rocks, juvenile conifers,
and tree stumps, which occurred most frequently as the control type.
To determine if lynx marked objects with certain characteristics more often than others when spraying urine, we used thepercentage of the characteristic type used on each transect as
the independent variable in the GLMMs. We tested each characteristic we recorded (Table 1), first overall for all objects,
then for each object type. For rocks, we also tested for lynx
use of rocks with or without moss and among different tilts ofrocks.
To determine if lynx selected for certain types of objects
and characteristics (i.e., used more often than available) whenspraying urine, we compared the percentage of object type orcharacteristic used per transect to the percentage of objects or
characteristics available per the same transect for the object
types for which we had enough samples (rocks, juvenile conifers, other vegetation, and tree stumps) in the GLMMs.
Therefore, the number of object types for our selection analyses was lower than in our use analyses. The analysis was done

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for every object type separately; the selection of characteristics
was tested per characteristic per object type and all object
types together.

Results
Overview
We followed 17 Eurasian lynx tracks (nmale = 11, nfemale = 4,
nunknown = 2) during six winters over a span of 13 years (n04–05 = 2, n06–07 = 5, n07–08 = 3, n14–15 = 1, n15–16 = 5, n16–17 = 1)
for a total of 91 km. On five occasions, we were able to follow
the track across multiple days. We documented urine marking(97.9%) more frequently than cheek rubbing (1.9%) or claw
marking (0.2%) (n = 620).
Types of objects sprayed with urine
Eurasian lynx sprayed urine significantly more often on rocks(t = 7.62, P < 0.0001), juvenile conifers (t = 5.32, P < 0.0001),
and tree stumps (t = 2.90, P = 0.0047) than other types ofobjects (Fig. 1). Rocks were used significantly more than allother objects, and juvenile conifers were used significantly
more than all objects other than rocks. Tree stumps were usedsignificantly more often than snow mounds, tree trunks, andhuman objects.
Characteristics of objects sprayed with urine
In our series of 27 analyses, 25 of the variables exhibited asignificant pattern (Table 3). Among all objects, characteristics that were used most include those that were 0.5–1 m inheight, facing up slope, on straight roads, oriented towards

Fig. 1 Types of objects used by Eurasian lynx for scent marking withurine spraying in the Dinaric Mountains, Slovenia (n = 607). Error bars
represent the standard error

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Table 3 The characteristics of objects that Eurasian lynx sprayed withurine, reported for all objects and the four most frequently used object
types. We report the variable name (see Table 1 for description of thevariables) and the results as a t value, P value, the characteristic that wasused most often, and the percent of times it was used compared to othercharacteristics used in the given object type
Variablet

P

CharacteristicUse

All objects
HeightSlope
Road curvature
Direction
Orientation

3.39
4.88
9.53
2.60
5.94

0.0014< 0.0001< 0.0001
0.0104< 0.0001

0.5–1 mUp
Straight
Southwest
Parallel

41.7%
57.9%
69.1%
20.5%
64.1%

Rocks
HeightSlope
Road curvature
Direction
Orientation
Moss
Tilt
Juvenile conifers
HeightSlope
Road curvature
Direction
Orientation
Tree stumps
HeightSlope
Road curvature
Direction
Orientation
Other vegetation
HeightSlope
Road curvature
Direction
Orientation

6.95
5.14
6.38
2.36
4.61
4.56
5.02

< 0.0001< 0.0001< 0.0001
0.02040.00010.00260.0002

0.5–1 mUp
Straight
East
Parallel
Moss
Vertical

57.4%
63.2%
63.6%
21.4%
66.1%
75.4%
71.8%

2.64
4.92
5.89
2.32
5.76

0.0119< 0.0001< 0.0002
0.0227< 0.0001

1–2 m
Up
Straight
West
Parallel

36.2%
67.8%
71.0%
24.1%
67.1%

3.64
–
4.06

0.0009–0.0006

0.5–1 m–Straight

40.9%
–
65.0%

2.6
3.02

0.01120.0068Southwest
Parallel

26.9%
49.2%

–
6.86
2.80
2.93
4.43

–
< 0.0001
0.00190.00490.0004–
Up
Straight
West
Parallel

–
88.3%
61.7%
36.0%
74.1%

southwest, and parallel to direction of lynx travel (Table 3).
Among objects of different types, these patterns held true except for direction in many cases, and juvenile conifers of 1–
2 m being used most often (Table 3). Among rocks, objects
with moss and vertical tilts were used most often (Table 3).
Objects selected (use versus availability)
When comparing the selection (use versus availability) of object types that were sprayed with urine (Fig. 2), we found thatjuvenile conifers were the only object selected significantly

Fig. 2 The pattern in selection of objects sprayed with urine by Eurasianlynx on forest roads, shown as a comparison of the percent of objects used(black; n = 106) and their availability (gray; n = 1417). Asterisks indicate
significant selection (*P < 0.05; **P < 0.01; ***P < 0.001), and error bars
represent the standard error

more often than available (t = 8.82, P = 0.0009). In contrast,
both rocks (t = − 3.72, P = 0.0205) and other vegetation(t = − 4.63, P = 0.0098) showed significant selection against
being used.
Among the characteristics of all objects selected (Table 4),
the height class 0.5–1 m was the only characteristic positively
selected for (t = 5.50, P = 0.0053), while the height class > 2 m
was selected against (t = − 2.98, P = 0.0408). Among rocks,
those with a height of 0.5 to 1 m were selected for (t = 2.89,
P = 0.0446); while rocks with a height of > 2 m (t = − 3.07,
P = 0.0371), those facing downslope (t = − 3.00, P = 0.0400),
and those with a sloping tilt were selected against (t = − 4.76,
P = 0.0089) (Table 4). Among juvenile conifers, those on
Table 4 The selection of objects that Eurasian lynx sprayed with urine,
as measured by the selection of characteristics compared to theiravailability. We report the variable name (see Table 1 for description of
the variables) and the results as a t-value and P-value, followed by thecharacteristic with the highest selection (shown as a percent increased or
decreased from expected use based on availability)
Variable
All objects
HeightRocks
HeightSlope
Tilt
Juvenile conifers
Road curvature
Other vegetation
HeightCharacteristictP

Selection

0.5 to 1 m
>2m

5.50
− 2.980.00530.040812.2%− 8.2%

0.5–1 m2.89

0.044640.1%>2m
Downslope
Sloping− 3.07− 3.00− 4.76

0.03710.04000.0089− 13.5%− 2.8%− 19.7%

Straight

3.49

0.025213.5%

1.0 to 2.0>2m− 3.42− 2.900.02680.0439− 29.9%− 15.0%Behav Ecol Sociobiol (2017) 71:136

straight curvatures of roads were selected for (t = 3.49,
P = 0.0252). Among other vegetation, those with height 1–
2 m (t = − 3.42, P = 0.0268) and > 2 m (t = − 2.90, P = 0.0439)
were selected against.

Discussion
The efficiency of scent marking, by creating marks with a highprobability of detection by conspecifics due to their conspicuousness and persistence, is likely an important aspect of theselection of objects scent marked by animals, including solitary felids. Our analyses found general support for all three ofour proposed hypotheses (Table 2). Lynx selected for objects
that are expected to better retain smell (juvenile conifers) andavoided sloping rocks which are more exposed to precipitation (Bpersistence hypothesis^). Lynx also selected for objectsof similar size as lynx, objects on straight road sections, andmost often marked sides parallel to their travel routes andvertical rocks covered with moss. According to our predictions (Table 1), such marking placement promotes detectability of the messages (Bdetection hypothesis^) and/or reduces
the energy expenditure needed for marking (Baccessibility
hypothesis^). Our study thus provides insight into the adaptive significance of scent-marking behavior in the Eurasianlynx and possible mechanisms behind the selection of marking objects to increase the effectiveness of scent marking.
We found that Eurasian lynx most often sprayed urine onrocks, followed by juvenile conifers (Fig. 1), confirming observations from Switzerland where lynx also most often
marked these objects (Vogt et al. 2016). However, by comparing the use of objects with their availability (Fig. 2), we
showed that lynx actually selected only for juvenile conifers,
while they selected against rocks. This could be explained by
our Bpersistence hypothesis,^ as wildcats also showed preferential selection of conifer species (in that case Juniperus
communis) (Ruiz-Olmo et al. 2013), which may be connectedwith the chemicals within the conifer slowing the release ofvolatile organic compounds in the urine. Our observations on
object selection also correspond to scent marking by othercarnivores, such as gray wolf (Canis lupus) (Barja 2003),
red fox (Vulpes vulpes) (Miguel et al. 2009), and giant panda(Ailuropoda melanoleuca) (Nie et al. 2012). In addition, theshape and the larger surface-to-volume ratio of conifers compared to rocks likely better retain scent as it increases theadsorption of chemicals in urine (more urine staying on thesurface instead of falling to the ground, which frequently
occurs in urine spraying by lynx on smooth surfaces; pers.
observation, see also video in supplementary data of Krofel
et al. 2017) and better protects it from the elements (Alberts
1992; Nie et al. 2012). Prolonged persistence of scent marks
on juvenile conifers would allow conspecifics to be able toreceive chemical message for longer periods, which would

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decrease the need to frequently refresh the scent marks, therefore increasing the efficiency of scent marking by lynx.
The frequent use but not selection for rocks as scentmarking sites could also be explained by our Bdetection
hypothesis.^ Given the large relative availability of rocks inour study area, this may make rocks that are lacking any otherdistinction less conspicuous and thus less attractive for scentmarking. Piñeiro and Barja (2012) found that wildcats preferentially selected for more visually conspicuous objects, which
likely increased the probability of detection for scent marks,
and similar studies have shown that detection appears to bealso important for other felids (Bothma and Le Riche 1995;
Ruiz-Olmo et al. 2013; Allen et al. 2014) and other carnivores(Barja 2009; Miguel et al. 2009; Nie et al. 2012).
While we observed avoidance of rocks more exposed toprecipitation according to the tilt of the marked face, there wasno clear selection for northward-facing faces. This contrasts
with observations of marking behavior of snow leopards(Ahlborn and Jackson 1986; Jackson 1996) and may be because the lynx habitats in Dinaric Mountains are less exposed
to weather than the snow leopard range in the Himalayas, or
because snow leopards frequently use scraping while scentmarking (Jackson 1996) and shelter is therefore also needed
to preserve the visual cues of the scrape (e.g., Allen et al.
2014).
When we analyzed characteristics of sites used for marking, we observed that lynx most often sprayed urine on rocks
and juvenile conifers, the side of the object facing up theslope, objects that were 0.5–1 m high and located on straightroad sections, and among rocks those covered with moss andwith a vertical face. When taking into account the availability,
we noted that lynx also selected for objects 0.5–1 m high andobjects on straight road sections, but avoided rocks, objects on
downward slopes and sloping sides of the rocks. Although
there was some overlap in use and selection, this suggests that
focusing research only on object use oversimplifies scentmarking, stressing the importance of measuring object availability and thus selection of objects when conducting scentmarking behavior studies.
Our use of snow tracking informs our understanding ofscent marking by Eurasian lynx and complements the previous studies that have been conducted with this (Vogt et al.
2016; Krofel et al. 2017) and other methods (e.g., Schmidt
and Kowalczyk 2006; Vogt et al. 2014). One limitation of
the snow tracking method was our difficulty in documenting
behaviors other than urine spraying, such as cheek rubbing,which camera trap studies have shown often occurs in conjunction with urine spraying (Vogt et al. 2014; LH and MK,
unpublished data; Online Resources 1 and 2). Another limitation is that because our study focused on winter (to use snow
tracking), our data is limited to this season, and selection may
be different in summer when leaves on young deciduous trees
and other objects are available. Our study also focused on lynx

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Page 8 of 9

marking behavior in the wild and did not measure persistence
and detectability of scent marks or accessibility of marking
sites directly. Future studies using an experimental framework
could help to determine more precisely how different objects
and variables affect the persistence of felid scent marks (e.g.,comparison of scent persistence among plants, rocks and otherobjects, and among different aspects and tilt of the marked
side of the object), how this affects the selection of objects
for scent marking by mammals and efficiency of scent marking, and whether these characteristics increase investigationby conspecifics.
We found that lynx used and selected objects and microlocations for urine spraying in a way that likely contributed
towards prolonging longevity of the scent message, increasing
detectability of the chemical message by conspecifics, andpromoting energy-efficient marking behavior. The efficiency
and success of scent marking is generally difficult to study inthe wild but has important implications for the fitness of individuals and populations. Our study also highlights the tradeoffs faced by the lynx in object selection, as the preferredmarking objects are often not readily available (juvenile conifers were available at only 17% of road sections). Lynx therefore need to use suboptimal marking objects to maintain thehigh scent-marking frequency throughout their territory thatwas reported for this species and is likely required for effective
intraspecific communication (mean scent-marking rate
7.1 urine sprays/km; Krofel et al. 2017). Understanding use
and selection of marking objects also has implications beyond
behavioral ecology, with applied aspects including designingeffective research and population monitoring schemes. These
often depend on the successful selection of sites for live captures, photo-trapping, and hair-snaring (Schmidt andKowalczyk 2006; Heurich et al. 2012; Krofel et al. 2013;
Zimmermann et al. 2013), which are further important forsuccessful conservation and management of endangered populations of Eurasian lynx and other felids.
Acknowledgments This study was partly financed by the Slovenian
Research Agency (grant no. P4-0059) and by the European Union
through INTERREG IIIA Neighborhood Program Slovenia/Hungary/
Croatia 2004–2006 (project BDinaRis^). We are grateful to P. Apps, U.
Fležar, L. Garamszegi, J. Javornik, A. Žagar, and an anonymous reviewer
for reviewing drafts of the manuscript and providing several usefulsuggestions that importantly improved the manuscript.
Compliance with ethical standards
Ethical approval All applicable international, national, and/or institutional guidelines for the care and use of animals were followed, and thework conforms to the legal requirements of the country in which it was
carried out.
Conflict of interest The authors declare that they have no conflict ofinterest. All sources of funding are acknowledged, and the authors do not
expect any direct financial benefits that could result from this publication.

Data availability The datasets generated during the current study areavailable from the corresponding author on reasonable request.

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