Behaviour (2015) DOI:10.1163/1568539X-00003270

brill.com/beh

Black bear marking behaviour at rub trees during thebreeding season in northern California
A. Preston Taylor a,∗ , Maximilian L. Allen b and Micaela S. Gunther aaDepartment of Wildlife, Humboldt State University, 1 Harpst Street,
Arcata, CA, 95521, USAb
Center for Integrated Spatial Research, Environmental Studies Department, University ofCalifornia, Santa Cruz, 1156 High Street, Santa Cruz, CA, 95064, USA* Corresponding author’s e-mail address: at87@humboldt.edu
Accepted 30 January 2015; published online ???

Abstract
We studied the marking behaviour of American black bears (Ursus americanus) during the breeding season 2013. Six remote video cameras captured 529 trapping nights. We collected behaviour,sex, and age class of bears rubbing on trees. Marking events (N = 31) were observed between 26
April and 27 July with a median of 12 June. The majority (96%) of marking events were performed
diurnally. All bears we could accurately identify to sex were males (N = 16) and 29 of 31 marking
bears were adults. The most frequent use of contact with substrate was bipedal marking followedby pede marking, quadrupedal marking. Bears used their back, neck, head, and cheeks in nearly
90% of observations while scratching and biting occurred in less than a third of observations. We
documented the novel behaviour ‘groin marking’. This study suggests rub trees are locations forchemical communication through a variety of marking techniques in forested environments.

Keywords
American black bear, breeding season, communication, remote-video camera, rub trees, scentmarking, Ursus americanus.

1. Introduction
Scent communication is an ideal method to broadcast messages when auditory or visual contact is made difficult due to thick foliage or features of
the terrain (Thiessen & Rice, 1976). Deposition of odours can be used todelineate territorial boundaries, find mates, avoid physical interactions, or to
avoid foraging in recently exploited areas (Henry, 1977; Gorman & Trowbridge, 1989; Allen et al., 2014). Information transmitted through odours© Koninklijke Brill NV, Leiden, 2015

DOI 10.1163/1568539X-00003270

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Behaviour (2015) DOI:10.1163/1568539X-00003270

may include species identification, sex and reproductive status, identities ofindividuals, relative age, and mood (Eisenberg & Kleiman, 1972). In carnivores, scent marking is likely used for multiple functions, and has been
demonstrated for use to delineate territorial boundaries, increase scavenging
efficiency, help conspecifics locate one another, and for inter and intra-group
communication (Peters & Mech, 1975; Henry, 1977; Rogers, 1987; SilleroZubiri & Macdonald, 1998).
Solitary carnivores must be able to find mates and deter intrasexual competitors, and behaviours exhibited to accomplish these goals can vary between sexes (Rogers, 1987; Bothma & le Riche, 1993; Clapham et al., 2012;
Allen et al., 2014). For example, both leopard (Panthera pardus) males andfemales scratch trees; however, male leopards spray urine on trees significantly more than females, and more frequently immediately before, during,
and after mating (Bothma & le Riche, 1993). Communication can be difficult
in forested environments, and as such, signals created may be intended fora specific purpose and contain multiple cues (Candolin, 2003). Furthermore,
the method and intent of marking behaviour may vary throughout the year
as the reason for communicating changes: females in oestrus, food larders,competition avoidance, or behavioural learning opportunities (Lloyd, 1979;
Clapham et al., 2012).
Bears scent mark in a variety of forms, including actively rubbing against
trees, rocks, or the ground, intentionally marking with their feet as they walk,
urinating and straddling saplings, urinating as they walk or passively on vegetation as they move through brush (Tschanz et al., 1970; Lloyd, 1979; Klieman, 1983; Rogers, 1987). Giant pandas (Ailuropoda melanoleuca) possessa waxy-sticky anal gland secretion and use a handstand position to apply theanal gland secretion to the substrate (Kleiman, 1983). Neither the brown bear
(Ursus arctos) nor the black bear (Ursus americanus) possesses an equivalent sticky anal gland secretion nor has been observed engaging in the scentmarking behaviour exhibited by the giant panda (Pocock, 1921; Rosell et al.,2011). Experiments with captive bears have provided detailed observationof methods used to deposit scent, temporal differences in marking between
sexes, the role of marking as a form of social communication (Tschanz et al.,1970), and marking as linked to the dominance hierarchy of the population(Rogers, 1977, 1987).
Marking, or rub, trees have an important role for communication in bear
species; however, there are few visual observations of bears engaging inA.P. Taylor et al. / Behaviour (2015)

3

marking events in the wild or captivity. From indirect observations, it has
been reported that marking on trees occurs more frequently during the breeding season for grizzly bears and black bears (Rogers, 1977; Burst, 1979;
Green & Mattson, 2003; Karamanlidis et al., 2007; Clapham et al., 2012),
and is apparently performed more frequently by males; although, after the
rut there is no difference between the frequency of marking for male andfemale grizzly bears (Rogers, 1987; Karamanlidis et al., 2007; Clapham etal., 2012). Interestingly, Clapham et al. (2012) also found females with cubs(<1 year old) increased their marking behaviour after the breeding season,
possibly to introduce cubs to adult male scent and marking techniques when
the chance of infanticide was lowest. Interspecific interactions also impact
marking behaviour, as black bears reduce their use of rub trees after grizzly bears mark them (Shaffer, 1971). Some rubbing events may result fromthe inherent curiosity of this intelligent omnivore. However, with few studies systematically recording bears marking trees in the wild, there may be
important behavioural aspects that are currently unknown.
We used remote video cameras to record marking behaviours of American
black bears at rub trees during the breeding season in northern California. In
this study we focused on the behaviours that American black bears exhibit
at rub trees; rub trees refer to trees that are used as scent marking locations.
Henceforth, marking events refer to behaviours recorded at rub trees. This is
the first study to investigate the marking behaviours of free-ranging American black bears using video from remote cameras. Our goal was to examine
the marking behaviours used during the breeding season to assess their frequency and duration, and the extent to which bears of different sex and age
differed in the frequency and intensity with which they used marking behaviours.
2. Materials and methods
2.1. Study area
We conducted our study in northwestern California in Redwood National
Park and adjacent Green Diamond Resource Company lands that are located north of the town of Orick, CA, USA, 78 km south of the Oregon–
California border. Redwood National Park (RNP) is a protected area encompassing 534 km2 , with 158 km2 of old-growth forest (Redwood National
Park, 2013a). Green Diamond Resource Company harvests and sells timber
products on lands adjacent to RNP, and manages its forests with sustain-

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Behaviour (2015) DOI:10.1163/1568539X-00003270

able practices that have resulted in a Forest Stewardship Council certification(GDRC, 2013). Due to timber roads, tree harvest locations, and regenerating
stands of young forests, the landscape is a patchier environment with moreincreased edge habitat than Redwood National Park.
The study area is comprised of coastal redwood (Sequoia sempervirens) dominated forests, and mixed coniferous-hardwood forests inland
and at higher elevations. Dominant trees of the park include big-leaf
maple (Acer macrophyllum), Douglas fir (Pseudotsuga menziesii), red alder(Alnus rubra), Sitka spruce (Picea sitchensis), and tan oak (Lithocarpus densiflorus), while common understory and herbaceous plants include
huckleberry (Vaccinium spp.), salal (Gaultheria shallon), salmonberry(Rubus spectabilis), skunk cabbage (Lysichiton americanus) and sword fern
(Polystichum munitum) (Redwood National Park, 2013b). Large mammals
that reside in the study area include black bear, black-tailed deer (Odocoileus
hemionus), elk (Cervus elaphus), bobcats (Lynx rufus), coyotes (Canis latrans) and pumas (Puma concolor) (Redwood National Park, 2013c).
The climate of the region is characterized by wet, cool winters and warm,
foggy summers. The majority of precipitation is received in winter months,
but coastal fog during summer condenses on trees and drips on the ground.
Average annual precipitation is 152–203 cm, and temperatures vary from
4–15°C (Redwood National Park, 2013d).
Black bear densities in northwestern California are some of the highest
reported for the species and can range from 1–2 bears/km2 (Matthews, 2002;
Early, 2010). Bears in the region maintain a home range but do not appear
to be highly territorial (Early, 2010). Home range size estimates for bears
near the study area range from 10.6–62.3 km2 for males and 3.6–17.3 km2
for females (Kellyhouse, 1980; Matthews, 2002; Early, 2010). Across its
geographic range, the black bear’s breeding season is consistent and ranges
from 25 May to 10 August with a peak in June and July (Jonkel & Cowan,
1971; Rogers, 1977).
2.2. Field methods
We deployed six remote video cameras with infrared flash (Truthcam 35,
Primos, Flora, MS, USA) to record marking events between 25 April and 9
August 2013 in order to encompass the breeding season. The six cameras
were active 24 h/day for a total of 529 trapping nights. Trapping hours were
not equally distributed across camera stations because of electronic malfunctions (from condensation inside the unit) and one camera being stolen. We

A.P. Taylor et al. / Behaviour (2015)

5located rub trees by walking along bear trails, and trees were determined
to be a rub tree by presence of a combination of hair, bite and claw marks,
wounds on the tree, and a depression of tracks leading to and from the tree
(Burst, 1979; Burst & Pelton, 1983; Elbroch, 2003). We set up each camera
to record bear visits and marking behaviours at a rub tree by placing themknee to shoulder height facing the rub tree. We subsequently changed 1 camera set up to 5 m high pointing down in order to stop bears from displacing
the camera during visits. We set the cameras to record 60-s videos with a
10-s delay between triggers, and we replaced batteries and memory cards
every 1 to 3 weeks, depending on how often cameras were capturing videos.
We defined a video event as each time a black bear was documented
on camera, and defined a marking behaviour event as each time a bear
exhibited one of the marking behaviours (Table 1) during a visit. We determined sex from external reproductive organs (testicles and penis or vulva),
Table 1.
Ethogram of marking behaviours exhibited by black bears, captured with remote video cameras, during the breeding season 2013 in northwestern California.
Behaviour

Description

Biting

The bear’s teeth are in contact with tree and the bearuses its teeth to remove bark or wood.
The bear rubs its back against the tree.
The bear rubs its neck, head, or cheeks against the tree.
The direction a bear faces during marking behaviours.
Direction can be dorsal, where the bear is standing
with its back to the tree, or ventral where its stomach isfacing the tree.
The bear uses its nose to smell footprints leading up toa tree or smell the tree.
The bear walks with a stiff-legged gait, deliberately
placing rear feet in same location as front feet, andtwisting feet into ground or shuffling footforward-backwards before taking the next step.
The bear’s claws make contact with the tree and areused to hold or scrape the tree.
How a bear stands during marking; marking can occur
from a bipedal stand, where the bear is standing on its
hind feet to rub the tree, or a quadrupedal stand, where
all four feet are in contact with the ground and the bearis rubbing its side against the tree.

Dorsal marking
Facial marking
Orientation during marking

Olfactory investigation
Pede marking

Scratching
Stance during marking

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Behaviour (2015) DOI:10.1163/1568539X-00003270

a vulva-patch of hair (M. Clapham, pers. comm.), swollen mammae (Larivière, 2001), or the presence of cubs. Age class was subjectively assigned
based on size to cub (<1 year), yearling (1–2 years), and adult (>2 years);
however, due to difficulty in assigning age class from video data we did notincorporate it into any statistical analyses. Identification of individual bears
was based on sex, size, spatial and temporal differences in the area and timeof event capture, and amount of dorsal hair loss. Cameras were distributed
at a distance to maximize independence among events. Three cameras wereclose enough to potentially capture the same individual; however, the highdensity of bears allowed us to capture multiple different animals on thesecameras.
2.3. Statistical analyses
We created an ethogram of marking behaviours by black bears that included
8 observed behaviours (Table 1). For each marking behaviour event werecorded occurrence, frequency and duration of the behaviours exhibited.
We analysed the distribution of marking behaviour events by date and time
period. First, we divided each month of the study into two equal periods andthen analysed the frequency of behaviour events using a generalized linear
model with Poisson link in program R (R Core Team, 2014). Second, we
divided each day (24 h) into 4-h time periods: 00:01–04:00, 04:01–08:00,
08:01–12:00, 12:01–16:00, 16:01–20:00 and 20:01–00:00. We then analysed
the frequency of behaviour events by time period using a 2 × 6 Fisher’s exact
test (Sokal & Rohlf, 1987), rather than a chi-square test to account for low
sample sizes in some time periods. We then did a post hoc comparison basedon diurnal, crepuscular and nocturnal time periods, with crepuscular defined
as within 1 h of sunrise and sunset and time between crepuscular during theday, diurnal and night, nocturnal. For each analysis with significant statisticalresults we calculated post hoc effect size as ϕ coefficients (Nakagawa &Cuthill, 2007) to measure the magnitude of the effect; we considered scoresof 0.10 small effects, 0.30 medium effects and 0.50 large effects (Cohen,
1992).
Next, we analysed the frequency of occurrence for each behaviour compared to others using 2 × 2 chi-square tests (Sokal & Rohlf, 1987). We
compared differences in the frequency of display of the stances used while
marking, including the display of pede marking (on the ground) before
marking to after marking on the tree, the display of bipedal marking to7

A.P. Taylor et al. / Behaviour (2015)

quadrupedal marking, and the display of dorsal marking to ventral marking. For each analysis with significant statistical results we calculated post
hoc effect size as ϕ coefficients, as above.
3. Results
Over the duration of the study, we captured 49 videos of bears that included
31 marking behaviour events at rub trees (Table 2). During marking events,
we assigned sex to 16 of 31 bears (51.6%) as male. We were unable toassign sex to the remaining 15 marking bears because either they did not face
the camera while marking or the video quality was too poor to distinguishnecessary details. We were able to confidently identify 12 individual bears
based on coloration, size, and patterns of hair loss. Adult bears (N = 29;
93.5%) were observed marking more than cubs or yearlings (N = 2).
Table 2.
Mean time spent in behaviour (s) in order of decreasing frequency (number of events pervideos), and 95% confidence intervals (CI) for marking behaviours of black bears, captured
with remote video cameras, during the breeding season 2013 in northwestern California.
All marking bears

Total video length
Bipedal marking
Dorsal orientation
Dorsal marking
Facial marking
Pede marking leaving tree
ScratchingOlfactory investigation
prior to rubbing
Olfactory investigation
while rubbing
Quadrupedal marking
BitingPede marking
approaching tree
Ventral orientationa
Groin markinga

Known malemarking bears

Mean (s)95% CI

Mean (s)95% CI

20.4
9.5
7.8
7.9
10.1
5.9
8.1
1.9

12.0–28.8
2.5–16.5
4.0–11.6
4.1–11.7
1.2–19.0
2.2–9.6−15.7–31.9−3.0–6.8

30.8
15.3
12.3
12.1
16.3
6.2
25.1
6.0

26.2–35.4
4.9–25.7
7.2–17.4
7.1–17.1
4.7–27.9
5.1–7.3−8.1–58.3
0.1–11.9

3.1

1.7–4.5

3.7

1.9–5.5

2.5
3.0
9.8

−14.2–19.2
2.6–3.4
8.2–11.4

4.0
3.0
9.8

1.1–6.9
2.6–3.4
9.3–10.3

24.4
25.5

n/a
n/a

48.7
n/a

n/a
n/a

a Ventral orientation and groin marking were only observed once.

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Behaviour (2015) DOI:10.1163/1568539X-00003270

Figure 1. Number of visits by black bears exhibiting marking behaviours at rub trees by
2-week intervals, observed with remote video cameras, during the breeding season 2013 innorthwestern California.

We observed 31 marking behaviour events between 26 April and 27 July
with a median of 12 June. The marking events varied significantly in theirdate of occurrence (F6,35 = 3.35, p = 0.0103), with 45.1% occurring from
1 June to 15 June (Figure 1). Marking events occurred between the hours
05:45–20:45 with a median of 10:43. Marking events varied significantlyin their time period of occurrence (p = 0.0187, ϕ = 0.26), with 53.8% of
events occurring from 08:01–12:00 (Figure 2). When compared by time
period, 83.9% of visits occurred during the diurnal time period, 16.1% were
crepuscular and 0% nocturnal.
Rubbing was displayed at 83.9% of visits, significantly more frequently
than pede marking (38.7%, χ12 = 11.49, p = 0.0007, ϕ = 0.46), olfactory
investigation (41.9%, χ12 = 9.95, p = 0.0016, ϕ = 0.43), facial rubbing(54.8%, χ12 = 4.86, p = 0.0275, ϕ = 0.32), scratching (22.6%, χ12 = 20.99,
p < 0.0001, ϕ = 0.61), or biting (9.7%, χ12 = 31.36, p < 0.0001, ϕ = 0.74)(Figure 3). Scratching was less frequently displayed than facial rubbing(χ12 = 5.51, p = 0.0190, ϕ = 0.33), while biting was less frequently displayed than pede marking (χ12 = 5.63, p = 0.0177, ϕ = 0.34), olfactory
investigation (χ12 = 6.82, p = 0.0090, ϕ = 0.37) and facial rubbing (χ12 =
12.47, p = 0.0004, ϕ = 0.48).

A.P. Taylor et al. / Behaviour (2015)

9

Figure 2. Number of visits by black bears exhibiting marking behaviours at rub trees by timeof day, observed with remote video cameras, during the breeding season 2013 in northwestern
California.

Figure 3. Frequency of marking behaviours by black bears during 31 marking events at rub
trees, captured with remote video cameras, during the breeding season 2013 in northwestern
California.

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Behaviour (2015) DOI:10.1163/1568539X-00003270

When pede marking was exhibited, it was performed significantly more
after rubbing (100% of events) than before rubbing (16.7% of events) (χ12 =
13.89, p = 0.0002, ϕ = 0.85). Bipedal stance was exhibited during 92.3% of
rubbing events, significantly more frequently than the 23.1% of quadrupedal
marking observed (χ12 = 22.77, p < 0.0001, ϕ = 0.70). Dorsal orientation
was exhibited during 100% of rubbing events, significantly more frequently
than the 4.0% of events in which bears also rubbed using a ventral orientation(χ12 = 43.38, p < 0.0001, ϕ = 0.96).
Five of six rub trees had a series of ground marks that were evidence ofprevious pede marking. The sixth tree, which lacked ground marks, only
had one marking behaviour observation during the study period. Three bears
that did not themselves mark investigated the ground marks longer than they
investigated the rub tree. Furthermore, some male bears were observed pedemarking past the rub tree then turning around to pede mark in the sameground marks before rubbing themselves against the tree. All six rub trees
were located along bear trails that were used frequently enough to create avisible path through the forest.
We also observed a novel behaviour we termed ‘groin marking’, which
has not previously been described in the literature. A juvenile black bear approached a marking tree, and initially exhibited quadrupedal marking before
reaching its rear legs back until they were nearly parallel with the ground(as in a push-up position). The bear then apparently made contact with theground with its lower torso or groin while continuing to rub the side of its
hip against the tree. The bear then pulled its rear legs under its body again
quadrupedal marking. At 33 s into the video, the bear stopped marking andsat against the tree, then continued marking at 42 s with its rear legs stretchedback behind it and vigorously rubbing the tree from its ribs along its hip.
4. Discussion
Rubbing was the most common marking behaviour exhibited by black bears
at trees, and bipedal stance was the most common position observed. Although we did observe a sow with a cub walk past a rub tree, among events
where we could identify the sex, all marking bears were male. These findings
support previous observations of marking during the breeding season being
performed primarily by male American black bears (Rogers, 1977, 1987;
Burst, 1979; Burst & Pelton, 1983) and are similar to findings for brown

A.P. Taylor et al. / Behaviour (2015)11

bears (Tschanz et al., 1970; Clapham et al., 2012). We observed very few instances of bears investigating rub trees without marking, possibly suggesting
communication may be intrasexual between male bears that mark (Clapham
et al., 2012). Black bears’ preference to mark in a bipedal stance more than inother positions was in agreement with observations of marking techniques bycaptive brown bears (Tschanz et al., 1970), although the quadrupedal stance
was also observed in this study.
Pede marking occurred in a little over a third of our observations, and may
have been more frequently observed if the cameras had been more sensitiveand faster to trigger, as some videos began with a bear at or almost at the rub
tree. This suggests that for black bears depositing scent, pede marking could
be nearly as important as rubbing against a tree. A few bears showed more
apparent interest in (more time spent investigating) ground marks than thetree, and after marking, some bears engaged in a very deliberate grinding of
their feet into the ground. This pede marking could be a method of deploying scent by male bears as they move across the landscape, similar to how
female bears are known to drip urine as they walk while in oestrus (Rogers,
1977, 1987). On one occasion, we noted pede marks from a male bear that
extended for approximately 400–500 m from the marking tree. Very little is
known about how this behaviour is used and if American black bears havean interdigital gland that leaves scent. On video, bears were clearly using
their noses to investigate the trail of pede marks. We hypothesize pede marking may be used as an ephemeral and moveable communication behaviour tomark or leave scent regarding what a bear is interested in (females in oestrus,
food larders, a carcass) along with more stable marking substrates like a rub
tree.
Marking behaviour was exhibited most frequently by adult bears during
diurnal hours, and was most frequent from 1 to 15 June. These findings
suggest that in our study area the peak of breeding season was in early June.
With the exception of one young bear, only adult bears marked trees. We
estimated the young bear to be 2 years old based on body size, and it was
one of only two individuals that did not mark diurnally. The juvenile wasalso the only bear to exhibit the novel groin marking behaviour. We notedbears on camera during nocturnal hours, but only two of those individuals
exhibited any marking behaviours. The diurnal nature of marking may reflect
the regular rhythm of activity by black bears in this area, which, in theabsence of human disturbances, is usually crepuscular or diurnal (Bridges

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Behaviour (2015) DOI:10.1163/1568539X-00003270

et al., 2004). Rub trees may be easier to find during the day because of thevisual stimuli on the marked tree (exposed wood from biting and scratching,frayed bark, and sap).
There may be more involved in scent marking at rub trees than we could
observe through the video recordings. Shaffer (1971) watched a black bearurinating during a marking event and Rogers (1977, 1987) could smell bearurine on a rub tree. However, we could not determine if bears were urinating
while marking, although in some cases the penis was apparent protruding outof the sheath during marking. Nor could we see if saliva was deposited when
facial marking or biting. Black bears do not possess the waxy anal gland secretions of giant pandas, and only recently was the anal gland secretions ofbrown bears determined to possibly code for sex (Rosell et al., 2011). American black bear marking is less clear because of the lack of external scentglands (Pocock, 1921; Burst, 1979); saliva, urine, or anal gland secretion
deposition while marking would help explain bear communication. Saliva
deposition is supported by the high frequency of facial rubbing observed
but is countered by the low frequency of biting. Likewise, if urine was usedduring scent marking we would have expected bears to stand in the ventralorientation to place urine on the tree, but ventral orientation was only observed once. Regardless of scents, most contact with trees resulted in some
fur trapped in bark or sap.
Our findings could have important implications for bear population monitoring. Active, noninvasive hair-snares lure an animal to the wire brush,
carpet, or barbed wire fence with bait or scent. Passive hair-snares take advantage of natural rubbing objects or den entrances (Kendall & McKelvey,2008). Biologists use DNA extracted from hair gathered from natural rub
trees to monitor populations (Schwartz et al., 2006; Karamanlidis et al.,2007), however behaviour of a species can bias passively gathered data toward one sex or age class, in this case, towards adult males in the population.
Because black bears are managed as a game species, it is important for managers to use appropriate techniques to assess their population structure andnumber and to understand their natural history and behaviours to set seasonsand quotas to match desired target population demographics and density.
In summary, American black bears preferred to mark in a bipedal stance,
but pede, quadrupedal, and groin marking were also exhibited. While inbipedal stance most bears used the dorsal orientation and rubbed their back,neck, head, and cheeks against the rub tree. Ventral orientation, scratching,A.P. Taylor et al. / Behaviour (2015)13

and biting were observed infrequently. Bears clearly displayed olfactory investigation of rub trees and ground marks near rub trees, implying scentcommunication occurred between bears visiting the rub trees. The majorityof marking events occurred during the diurnal time period, with more thanhalf occurring between 08:01 and 12:00. A novel behaviour, groin marking,was engaged by the only young bear observed to mark in the study. This behaviour was unique among our observations and is likely a cryptic behaviour
that is rarely used. Further investigations should research scent marking ofindividuals of known sex, age, and reproductive status throughout the entire non-denning period. A finer-scale mapping and observation of all rub
trees within a set of home ranges may further illuminate our understandingof black bear communication.
Acknowledgements
We thank M. Clapham and D. Early for providing various aspects of assistance during study design, field data collection, analysis and manuscript
completion. Humboldt State University stockroom manager, A. Desch, assisted in rectifying some technological issues with the cameras and T.
Holmes Jr. contributed to the editing of the manuscript. We thank Redwood
National Park and Green Diamond Resource Company for allowing fieldwork on their land.
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