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Vigilance is an aspect of animal behaviour, which is often underrepresented in camera trap studies. In the current study, we provide preliminary camera trap data analysis on the differences in vigilance behaviour in two areas of Vitosha Mountain, Bulgaria (with and without hunting pressure). Our results suggest that in locations where hunting is permitted through the year, roe deer tend to be more vigilant (explained by the heightened perceived risk) but some of them are more sedentary, spending relatively longer periods of time in front of the camera trap. This could be attributed to the supplementary feeding in the hunting area, which results in higher densities of ungulates (thus increased competition and consequently smaller home ranges)
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Annuaire de l’Université de Soa “St. Kliment Ohridski”
Faculte de Biologie
2016, volume 101, livre 4, pp. 23-32
Youth Scientic Conference “Kliment’s Days”, Soa 2015
1 – Department of Zoology and anthropology, Faculty of Biology, Soa University “St.
Kliment Ohridski”, Soa, Bulgaria
2 – Nature Park Vitosha, Soa, Bulgaria
3 – Advanced Wildlife Technologies and Management, Soa, Bulgaria
* Corresponding author:
Keywords: vigilance, behaviour, roe deer, hunting
Abstract: Vigilance is an aspect of animal behaviour, which is often underrepresented
in camera trap studies. In the current study, we provide preliminary camera trap data
analysis on the differences in vigilance behaviour in two areas of Vitosha Mountain,
Bulgaria (with and without hunting pressure). Our results suggest that in locations where
hunting is permitted through the year, roe deer tend to be more vigilant (explained by the
heightened perceived risk) but some of them are more sedentary, spending relatively longer
periods of time in front of the camera trap. This could be attributed to the supplementary
feeding in the hunting area, which results in higher densities of ungulates (thus increased
competition and consequently smaller home ranges).
Camera traps have been used extensively to study biodiversity, species
richness, distributions and habitat use. In recent years more and more studies
were focused on animal behaviour issues, such as reproductive behaviour, feeding
behaviour, intraspecies and interspecies interactions (competition, predation,
etc.) and the effect of human-induced disturbance on all of these processes.
The vigilance behaviour exhibited by many species that leave the safety of
their shelters to forage is relatively underrepresented in these studies. Vigilance
is a type of behaviour associated with heightened perceived risk either by
competitors, predators or humans. It is often costly during foraging as it decreases
the time available to locate and consume food resources. Therefore, there is a
trade-off between the two, which could be inuenced by a number of factors,
such as food availability, predator densities, disturbance or hunting pressure,
habitat visibility etc.
Most of the existing studies regarding vigilance behaviour focus on ungulates
and are working on a single area with or without hunting/predation pressure
(Altendorf et al., 2001, Le Saout, 2015) or during or outside the hunting season
(Benhaiem et al, 2008). To our knowledge, our study is the rst to study the
differences in vigilance, relative to hunting pressure by comparing camera trap
data from two sites sharing similar habitat characteristics, where one is in a
hunting reserve (hunting is allowed through the year) and in the other hunting is
allowed only during open season.
Study area
The study sites are located in Nature Park Vitosha, Bulgaria (N 42° 33’ 44”, E
23° 17’ 9”), on the southern slopes of the mountain. The study sites were labelled
Zone 2 and Zone 6 for consistency with previous work. Zone 2 is in the area
above Bosnek village, in the premises of the Vitoshko-Studena Hunting Reserve,
whereas Zone 6 is located above Zhelezhnitsa village. Hunting is permitted
throughout the year (and supplementary food is provided – e.g. corn) within the
area of the Hunting Reserve, whereas in the other study area (serving as a control),
hunting is restricted to the open season (October – February). Both study areas
are inhabited by wolves (Canis lupus) and their effect on the roe deer’s behaviour
is presumed to be similar in the two zones.
Camera trapping
20 camera traps (Ltl Acorn 5210) were deployed in the two study areas (10 in
each zone) between May and September 2015 (Fig. 1). The camera traps were set
up on animal trails in forest habitats, according to a predetermined grid (Kilshaw
and Macdonald, 2011). They were programmed to take 3 photos and a 10-sec
video when activated by a passing animal, allowing the analysis of behaviour.
The camera traps were checked regularly to replace batteries and memory cards.
A standard form was lled for each camera trap location, including information
on the habitat characteristics. During the day, visibility was estimated (following
the method used by Le Saout, 2015) by using a 1m pole with 10 alternating
white and red 10 cm stripes, which was placed directly in front of the camera
trap. Visibility was assessed as the number of stripes visible from a distance of
10 m in the four cardinal directions. A visibility index was then estimated as the
proportion of visible stripes relative to the total number of stripes (ranging from
0 to 1, where 0 is a dense forest with low visibility and 1 is an open forest with
high visibility). For the analysis of the behaviour during different parts of the
day, 3 categories were used: day – the time between 30 min after sunrise and 30
min before sunset; twilight – the time within 30 min before and after sunrise and
sunset; night – the time between 30 min after sunset and 30 min before sunrise.
The exact times of sunrise and sunset were taken from the Astronomical calendar
of the Bulgarian Air Force (Bulgarian Air force – Meteorological Center, 2015).
Figure 1. Map of the camera trap locations in Zone 2 and Zone 6
Behavioural data and Statistical Analysis
The resulting photos were imported and analysed through CameraBase 1.6.
(Tobler, 2013) translated into Bulgarian and complemented to adapt the needs
of the study (Zlatanova 2014, unpublished). A total of 652 independent roe deer
registrations were recorded in 2124 camera trap nights. Relative abundance index
(RAI) was calculated for the two zones as the number of roe deer registrations per
100 camera trap days (ctd). For each registration, the following parameters were
estimated: total time in front of the camera (sec), time spent displaying vigilant
behaviour (sec), time spent displaying non-vigilant behaviour (sec) and the ratios
between them. Vigilant behaviour is described as the posture of the animal where
its head is above shoulder level and it’s scanning the surroundings (Appendix
Fig. A1, a). Non-vigilant behaviour is any other behaviour – including grooming,
browsing, feeding etc. (Appendix Fig. A1, b). Behaviour was analysed only when
the head of the animal was in the frame. Photos and videos displaying roe deer,
but not suitable for behavioural analysis were included in “time spent in front of
the camera”, but excluded from all other calculations. Roe deer behaviour was
successfully identied in 88,51% of the registrations, whereas the other 11,49%
were labelled as “unknown behaviour”.
Statistical analyses were performed in R v. 3.1.0 (R Core Team, 2015).
a) b)
Figure A1 Camera trap photos of a male roe deer displaying
a) vigilant and b) non-vigilant behaviour
A summary of the resulting camera trap photos and the behavioural data
derived from them is presented in Table 1. Due to malfunctions of part of the
camera traps the total operational time (camera trap days) is different between the
two zones. The RAI shows a considerable difference in the abundance of the roe
deer. In Zone 2 (within the Hunting reserve) the index is much higher, indicating
a more abundant population, which is expected considering the supplementary
food provided to the animals there.
Table 1. Summary of the camera trap and behavioural data
Zone 2 Zone 6
Registrations of roe deer 478 174
Camera trap days 1158 966
RAI (registrations/ 100 ctd) 41.28 18.01
Number of registrations displaying
vigilant behaviour 207 75
Percentage of registrations displaying
vigilant behaviour 43,31% 43,10%
The number of registrations in the camera trap locations is mapped and
presented in Fig. 2.
Figure 2. Roe deer registrations in the two zones
The total time spent in front of the camera (Fig. 3a) appears to be shorter in
Zone 2 than in Zone 6 when comparing the median values. There is, however,
an interesting distinction to be made – the presence of outliers with high
values of time spent in front of the camera in Zone 2, one even reaching more
than 2 minutes. It seems unexpected at rst to observe individuals spending
comparatively such a long time in one place, especially when faced with hunting
pressure and disturbance. In our case, this could be attributed to the difference
in the abundance of roe deer (and other ungulates, notably the red deer Cervus
elaphus, which is virtually absent from Zone 6) between the two zones. The high
roe deer density and the added presence of red deer in Zone 2 lead to increased
competition for space and food. That in turn limits the territory that is available
for foraging to a single individual and causes it to spend more time in the same
location utilizing the accessible resources at hand to the maximum.
The total percentage of registrations displaying vigilant behaviour in the two
zones are very similar, but the differences are visible in the analysis of the duration
and proportion of vigilant behaviour in each observation (Fig. 3). The box plots
for the duration of vigilant events (Fig 3b) show little difference between the
zones in terms of the median and the spread of the distributions. However, a larger
number of outliers are present in Zone 2, some holding values 2-3 times bigger
than those in Zone 6. This could be explained again with the higher densities
(resulting in smaller home ranges and the need to avoid competitors) in Zone 2,
and the data points to increased vigilance in the individuals that spend more time
in front of the camera.
The analysis of the proportion of time spent vigilant in each registration (Fig.
3c) shows a noticeable difference in the two zones. Vigilance levels are higher
in the zone with hunting pressure with a median of 0,67 and much lower in Zone
6 (median = 0,50) which emphasizes the role of hunting on roe deer behaviour.
This is in agreement with the result of Sönnichsen et al. (2013) and Benhaiem et
al (2008) that report heightened vigilance during the hunting season.
Figure 3. Effect of hunting pressure on roe deer behaviour. Total time spent in front of
the camera (a), duration (b) and proportion (c) of time spent vigilant in Zone 2 (in the
Hunting enterprise, hunting pressure through the year) and Zone 6 (control, without
hunting pressure outside of the open season)
When considering the different times of day, further patterns emerge. The
number of registrations displaying vigilance during the day, twilight and night
differs signicantly between the two zones 2 = 7,215; d.f. = 2; p < 0,05). The
proportion of the time spent vigilant (Fig.4) is higher and more variable during the
day and night in Zone 2, whereas higher levels of vigilance are observed in Zone
6 during twilight. The effect of hunting is reected in higher vigilance during the
day. The increased vigilance during the night in Zone 2 could be explained by
the concentrations of ungulates in the area (due to supplementary feeding) which
attract carnivores. In the conditions of high hunting pressure in this area during
the day, the wolves are limited in their activity patterns and need to forage during
the night. Under normal conditions (in the control Zone 6) the wolves are active
predominantly in twilight, which is reected in the higher vigilance levels of the
roe deer there.
Figure 4. Proportion of time spent vigilant at different times of day in:
a) Zone 2 – with hunting pressure and b) Zone 6 – without hunting pressure.
The roe deer in Zone 2 are more vigilant during the day and twilight than
during the night, which supports the conclusion of Eccard et al. (2015) in their
similar results in Germany. The authors suggest that this is a long-term adaptation
to daytime hunting. These results are also in agreement with those of Sönnichsen
et al. (2013) from the Białowieza Primeval Forest in Eastern Poland.
With regards to the visibility (Fig.5), in the hunting zone locations with
denser forests tend to have roe deer registrations with higher levels of vigilance,
whereas in the non-hunting zone vigilance levels are relatively stable in the
different visibility classes. This is in agreement with the ndings of Benhaiem et
al. (2008) that during the open season roe deer are less vigilant when they were
close to woodland, but this is not the case outside the open season.
Figure 5. Proportion of time spent vigilant at different times of day in:
a) Zone 2 – with hunting pressure and b) Zone 6 – without hunting pressure.
In locations where the forest is relatively dense (forest visibility class 0.20
0.40) roe deer are more vigilant in the hunting zone. Such habitats provide
concealment to hunters and roe deer need to be more alert in order to spot a
potential threat early enough. In more open forests (class 0.60 – 0.80) there is a
reverse relationship – with higher vigilance levels in the non-hunting zone where
the only threat can be attributed to predators. In the open forest with very high
visibility (class 0.80 – 1.00) the vigilance levels are similar.
In Zone 2 the percentage of registrations displaying vigilant behaviour are
lower in the open forests than in the dense forests which points at visibility as one
of the factors that determine roe deer behaviour. In conditions of high visibility,
the animal is capable of detecting danger much easier and thus does not need to
be alert as long. This is especially true in Zone 2, where the main threat are the
hunters, who can easily be heard and seen in an open forest. These results are in
agreement with the conclusions of Altendrof et al. (2001) for the behaviour of the
mule deer in Idaho, USA and those of Le Saout (2015) for the Sitka black- tailed
deer in Canada. Kuijper et al. (2014), however, suggest that olfactory cues (in
their case wolf scat) are more important than visual ones when assessing risk in
dense forests.
Additional environmental and habitat variables could be studied in order to
further understand the dynamics of roe deer behaviour. The seasonal shifts in
territoriality, hunting pressure, foliage (altering visibility) and food availability
should all be taken into account when attempting to explain the differences in roe
deer vigilance. Roe deer density, presence of other ungulates acting as competitors
(red deer), as well as carnivores, could also play an important role. Furthermore,
it is interesting to test the effects of characteristics such as sex, age and group size
on vigilance behaviour (Lashley et al. (2014) provide an insight on white-tailed
deer vigilance in these aspects).
The results of the current study suggest that hunting pressures does cause
changes in the behaviour of roe deer that is reected in heightened vigilance not
only during the day (when hunters are active), but also at night. Forest visibility
plays a role in determining vigilance levels, mainly in the hunting zone. Due to
the high density of the roe deer population in the hunting zone (caused by the
abundant supplementary food provided by the Hunting reserve) some individuals
are limited in space by their competitors. They tend to spend more time in the
same location and show high levels of vigilance.
Acknowledgements: This work was supported by project „Ecological and behavioural
aspects of representative species of reptiles and mammals in model Natura 2000 zones”
(Contract № 167/17.04.2015), funded by the Fund for Scientic Research of Soa
University, and by the Directorate of NP Vitosha.
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... Подобно на случая с дивата свиня, всички наблюдения на благороден елен и сърна в двойка са извън периода на най-интензивна активност на елена. Други изследвания на територията на страната (в ПП "Витоша") показват, че там пиковете в активността на двата вида съвпадат почти напълно (Doykin et al., 2016). ...
... Присъствието и активността на хора и домашни или безстопанствени кучета на територията на ПП "Витоша" са много по-интензивни в сравнение с тези в НП "Пирин". Наличието на кучета също може да се причисли към антропогенните фактори, тъй като независимо от статута си (домашни, безстопанствени или полудиви) те разчитат поне до известна степен на храна, предоставена от хората (Doykin et al., 2016;Soto & Palomares, 2015). Получените стойности за коефициента на припокриване в денонощната активност на изследваните видове с хората и кучетата, регистрирани в двата парка, както и припокриването в активността на всеки вид между двата парка са представени на Табл. ...
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Behavioural ecology of mammals studied with camera traps Summary The behavioural ecology of mammals is an important element of their study and conservation. Such data for the species inhabiting Bulgaria is largely missing. The camera traps provide a unique insight into the behaviour of wild mammals and can help begin filling this gap in the knowledge. Studies on the influence of abiotic, biotic and anthropogenic factors on the behaviour of 9 selected species in Bulgaria are presented in this thesis. The most frequently registered species (indicated by the estimated detection rates) in the studied mountain areas in Bulgaria are roe deer, red fox, European badger, wild boar, wood mice, stone marten, red squirrel and European hare. The GAMM models indicate that the influence of the abiotic factors is stronger for the smaller studied species – the red fox and the roe deer. The activity rates of the red deer in the study areas is not significantly influenced by the abiotic factors. The wild boar’s activity rates are positively influenced mainly by humidity and rainfall because it is well adapted to life in humid conditions (due to the characteristics of its fur and hoofs). The roe deer’s activity is positively influenced by the increase in temperature, wind speed and atmospheric pressure. This is due to a complex adaptation against adverse meteorological conditions and avoidance of predators. The activity of the red fox is positively influenced by the increase in temperature, humidity and atmospheric pressure – an adaptation against adverse meteorological conditions and towards enhanced foraging (during the increase in rodent activity). A new method based on 2D Kernel Density Estimation graphs is proposed to analyse mammal activity patterns throughout the year. The study at feeding sites in Western Rhodopi Mts. indicates that a variety of non-target species utilise the resources, including ones of conservation like the brown bear. Its presence and activity do not impact the visitations of other species. The mammals attending the feeding stations alter their foraging strategy depending on the trade-off between energy intake and risks associated with predators, competitors and hunters. The large omnivores and herbivores dominate the feeding stations. When two species attend the feeding station simultaneously typically the smaller species retreats first. The wild boar’s herds are the most intimidating and deter visits even by the brown bear (especially young individuals). The hunting pressure influences the roe deer’s behaviour, indicated by increased vigilance both during the day and the night. The red fox, wildcat and red squirrel are most influenced by anthropogenic disturbance. They avoid parts of the day (mainly during the day) when the humans and dogs are most active. The red fox and the wildcat alter also their habitat selection depending on the presence of anthropogenic disturbance. They avoid mixed forests (where humans and dogs were most frequently observed) and select for the deciduous forests (where the pressure is weaker).
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Anti-predator responses by ungulates can be based on habitat features or on the near-imminent threat of predators. In dense forest, cues that ungulates use to assess predation risk likely differ from half-open landscapes, as scent relative to sight is predicted to be more important. We studied, in the Białowieża Primeval Forest (Poland), whether perceived predation risk in red deer (Cervus elaphus) and wild boar (Sus scrofa) is related to habitat visibility or olfactory cues of a predator. We used camera traps in two different set-ups to record undisturbed ungulate behavior and fresh wolf (Canis lupus) scats as olfactory cue. Habitat visibility at fixed locations in deciduous old growth forest affected neither vigilance levels nor visitation rate and cumulative visitation time of both ungulate species. However, red deer showed a more than two-fold increase of vigilance level from 22% of the time present on control plots to 46% on experimental plots containing one wolf scat. Higher vigilance came at the expense of time spent foraging, which decreased from 32% to 12% while exposed to the wolf scat. These behavioral changes were most pronounced during the first week of the experiment but continuous monitoring of the plots suggested that they might last for several weeks. Wild boar did not show behavioral responses indicating higher perceived predation risk. Visitation rate and cumulative visitation time were not affected by the presence of a wolf scat in both ungulate species. The current study showed that perceived predation risk in red deer and wild boar is not related to habitat visibility in a dense forest ecosystem. However, olfactory cues of wolves affected foraging behavior of their preferred prey species red deer. We showed that odor of wolves in an ecologically equivalent dose is sufficient to create fine-scale risk factors for red deer.
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We applied optimal foraging theory to test effects of habitat and predation risk on foraging behavior of mule deer (Odocoileus hemionus) subject to predation by mountain lions (Puma concolor). We predicted that deer would spend less time foraging, have higher giving-up densities of food (GUDs), and have higher vigilance behavior when occupying patch edges than when in open and forest interiors. We also measured GUDs in 3 microhabitats within 3 forest types. We used pellet-group surveys to estimate habitat and microhabitat use, and we assessed vigilance behavior with automatic camera systems. The GUDs (perceived predation risk) were greater in forests of Douglas fir (Pseudostuga menziensii) than moun-tain mahogany (Cercocarpus ledifolius). In forests of Douglas fir, GUDs were greatest in the forest interior, declined at the forest edge, and were lowest in the open microhabitat. Microhabitat features did not influence GUDs in the mountain mahogany forest. Pellet-group data indicated more activity in the open than in the edge or forest. Based on pho-tographs, deer were more vigilant at forest edges than in open and forest areas. We con-cluded that deer are responding to predation risk by biasing their feeding efforts at the scale of habitats and microhabitats and altering their habitat-specific patterns of vigilance behavior.
In natural environments, predation risk varies over time. The risk allocation hypothesis predicts that prey is expected to adjust key anti‐predator behaviours such as vigilance to temporal variation in risk. We tested the predictions of the risk allocation hypothesis in a natural environment where both a species‐rich natural predator community and human hunters are abundant and where the differences in seasonal and circadian activity between natural and anthropogenic predators provided a unique opportunity to quantify the contributions of different predator classes to anti‐predator behaviour. Whereas natural predators were expected to show similar levels of activity throughout the seasons, hunter activity was high during the daytime during a clearly defined hunting season. According to the risk allocation hypothesis, vigilance should then be higher during the hunting season and during daytime hours than during the non‐hunting season and night‐time hours. Roe deer (Capreolus capreolus) on the edge of Białowieża Primeval Forest in Eastern Poland displayed vigilance behaviour consistent with these predictions. The behavioural response of roe deer to temporarily varying predation risks emphasises the behavioural plasticity of this species and suggests that future studies of anti‐predator behaviour need to incorporate circadian variation in predation pressure as well as risk gradients of both natural and anthropogenic predators.
The mortality risk from hunting/predation should increase animals' vigilance and modify their selection of feeding sites. This risk may thus be costly if vigilance interferes with feeding and/or if animals select poorer but safer feeding sites. We observed the vigilance behaviour of roe deer, Capreolus capreolus, feeding in a fragmented landscape during and outside the hunting season and compared food availability and local landscape features at these feeding sites with random paired sites. Roe deer spent more time vigilant during the hunting season than outside it. During the hunting season, vigilance decreased as the woodland extent within an 800 m radius increased, but this was not the case outside the hunting season. Vigilance decreased with increasing distance to houses, both during and outside the hunting season. When food is abundant, interference with feeding may be low because animals can simultaneously process food (chewing) and be vigilant. During the hunting season, the total time spent vigilant while chewing increased with increasing food abundance to a lesser extent than outside the hunting season, suggesting a higher level of costly exclusive vigilance during the hunting season. Outside the hunting season animals selected feeding sites that provided more food, but during the hunting season, as risk (proximity to houses) was positively correlated with food availability, animals no longer selected feeding sites on the basis of food availability. Taken together, our results indicate that roe deer trade off risk avoidance for food availability in hunted populations.