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Electronic Supplementary Material
Directional preference may enhance hunting accuracy in foraging foxes
Jaroslav Červený1, Sabine Begall2, Petr Koubek3,1, Petra Nováková1, and Hynek Burda2,1*
1
Department of Forest Protection and Game Management, Faculty of Forest Protection and Wood Sciences, Czech University of Life Sciences, Kamýcká 129, 165 21 Prague 6, Czech Republic, 2 Department
of General Zoology, Faculty of Biology, University of Duisburg-Essen, 45117 Essen, Germany; 2 Institute of Vertebrate Biology, CAS, Květná 8, 603 65 Brno, Czech Republic,
* Author for correspondence ([email protected]).
MATERIAL AND METHODS
Hunting behaviour ("mousing") was observed between April 2008 and September 2010 in 84 (70 adult
and 14 juvenile) red foxes (Vulpes vulpes) in 65 localities in the Czech Republic, in different habitats, at
different day and night times. Several individuals at one locality, although not in the same place were observed repeatedly throughout the year. On the other hand, since a territory is shared by a pair of foxes, we
cannot exclude that in some cases two different individuals were observed in the same locality. Seven individuals were involved also in a telemetry study and wore collar radio transmitters (transmitting at 151
MHz) and most foxes could be identified by individual characteristics. Foxes were not aware of the observer. Altogether 23 experienced hunters and wildlife biologists (including the authors) participated in
the project and provided independent recordings (see below)). The body orientation (alignment) while
preparing for a jump was recorded in altogether 592 hunting jumps in 95 hunting series. (In fact the
"mousing" jump was sometimes followed by several short jumps in quick sequence, if the prey escaped
the first jump, but these following short jumps were already guided by sight and were not included in
these analyses.) Furthermore, the first, the middle, and the last (and thus also successful) jumps of a particular hunting series were analyzed separately. We used the Watson-Williams F-Test to compare mean
angles of foxes with transmitters and those without transmitters and also adult and juvenile foxes. Circular statistical analyses were performed with Oriana 2.0. Time, climatic factors (temperature, wind, sun position, light intensity, precipitation), habitat, terrain, vegetation of the prey were recorded. Two observed
foxes hunting under or in the vicinity of high voltage power lines were excluded from further analysis.
Independent observers recording different animals at different localities, at different times, etc.
(see above) made principally the same observations. There were no significant differences between observations made by J. Červený (n=235), P. Koubek (n=108), and 21 other observers (n=249) (multisample Watson-Williams F-test, F=0.147, p=0.864). A subset of observations were carried out blind:
>50% of the data (all the data by 21 independent observers and a part of initial observations by P. Koubek) were collected by "naive" observers who actually thought that we were interested in studying the effect of wind and (polarized) light.
Addenda and Notes to RESULTS AND DISCUSSION
(1) Mean angles of foxes with and without radio telemetry collars were not significantly different from
each other (Watson-Williams F-test; F=0.012; p=0.912, n=84). There was no difference in the orientation
of jumps between juvenile and adult foxes (Watson-Williams F-test; F = 3.008; p=0,087; n=82; two foxes
with unidentified age were excluded).
(2) The mean vector calculated over the last (and usually successful) jumps in a hunting series was
10±86° (n=95 hunting series of 84 foxes) and deviated also significantly from random distribution. In
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comparison, the mean vector of the first jumps in a hunting series was 44±75°, that of the middle jumps
in a hunting series was 54±92°, all vectors deviating highly significantly from random distribution.
(3) We divided our data set into two groups: a) hunting in low vegetation (like in harvested fields and
mowed meadows) and in winter fields with no snow cover and b) hunting in high vegetation or high snow
and conducted a post hoc analysis. It was, however, no more possible to reconstruct the situation for each
particular jump. Thus, even in situations when there was generally low vegetation there may have been
also mousing in islands of higher grass (and vice versa). When hunting in high vegetation or under snow
cover, the fox relies on its hearing, in low cover it may also see its prey, but auditory localization is not
excluded. See Table 1 (ESM) and Fig 1 (main document) for results of the analysis.
(4) In 200 (out of 592) jumps, the immediate success or failure was (or could be) recorded. Apparently,
foxes tend to orient their jumps in high cover more than in low cover (when they can orient also visually)
and NNE-oriented jumps are more successful. See Table 1 (ESM) and Fig 1 (main document) for results
of the analysis.
n
mean
angle(µ)
SD
vector
length (r)
Rayleigh
test (Z)
Rayleigh
test (p)
all
means
jumps
all
all
means
low cover
high cover
success
ful
unsuccessful
success failure success failure
of all
jumps
jumps
hunting
series
95
117
83
78
41
39
42
42.6°
31.3°
61.2°
50.3° 55.6° 18.9° 67.7°
592
42.6°
of all
jumps of
foxes
84
42.3°
86.3°
0.322
62.3°
0.553
64.0°
0.536
83.7°
0.344
87.5°
0.312
97.8°
0.233
97.1°
0.238
57.6°
0.603
79.3°
0.383
61.331
25.72
27.281
13.987
8.155
4.233
2.314
14.174
6.171
<1E-12
6.76E-12
1.42E-12
8.42E-07
2.87E-04
0.015
0.098
2.02E-07
0.002
Table 1. Statistical analysis of the recorded directions of mousing jumps, particularly with regard to the height of
the vegetation or snow cover, and with success or failure of the respective jumps.
(5) In addition to the correlation between the parameters “absolute time of day” and “direction of fox
jump” we split our data set into six categories representing relative times of day (i.e. before sunrise,
around sunrise, morning, afternoon, around sunset, after sunset, (estimated according to the calendar
<http://calendar.zoznam.sk/sunset-cz.php>) (cf. ESM: Fig. 1, Table 2). There was no significant differences between the six categories (multi-sample Watson-Williams F-Test F=0.788; p=0.559).
There were also no such differences even if only jumps in low vegetation or in winter fields without snow cover i.e. under conditions when also vision could have played a role (see above), were analyzed. It should be pointed out that in higher vegetation or when there is snow cover, the prey cannot see
the fox or its shadow. A fox jumps at the distance which is usually 2-3 times longer than its height. Only
a small proportion of observations were done, when the shadow was (theoretically) longer than 3 height
units. Last but not least, foxes do not usually hunt in sunny times, and indeed virtually all observations
were done on cloudy days, or before sunset or after sunset, and in most cases in areas where the horizon
was shaded by forest or mountains so that even at the time of sunset or sunrise on cloudless days when
the shade is long, the low sun is no more directly visible and hence also does not produce any shadows.
before around morning afternoon around after
sunrise sunrise
sunset sunset
3
n
mean angle (µ)
SD
vector length (r)
Rayleigh test (Z)
Rayleigh test (p)
107
48.8°
86.2°
0.322
64
56.9°
83.7°
0.344
116
31.2°
85.9°
0.325
100
45.0°
79.3°
0.383
71
48.1°
81.9°
0.36
107
38.7°
98.8°
0.226
7.154
7.587
12.257
14.696
9.211
5.464
7.81E-04
5.07E-04
4.75E-06
4.15E-07
9.99E-05
0.004
Table 2. Statistical analysis of the recorded direction of mousing jumps with regard to the relative time of
the day.
Figure 1. Angular data revealing the NE alignment of mousing foxes independent of the time of day. The
direction of the arrow represents the mean vector of angular data (µ), length of the arrow represents the rvalue (length of the mean vector), and inner circles indicate the 0.05-level of significance.
(6) There was no apparent difference in directional preference of mousing jumps between different seasons of the year (ESM: Fig. 2, Table 3).
season
dates
n
mean angle (µ)
SD
vector length (r)
Rayleigh test (Z)
Rayleigh test (p)
spring
summer
autumn
winter
breeding season
mating season
16.03.-15.06.
16.06.-15.09. 16.09.-15.12. 16.12.-15.03.
99
203
267
23
44.5°
36.8°
43.1°
62.4°
98.6°
91.7°
80.2°
64.0°
0.228
0.278
0.376
0.535
5.126
15.706
37.663
6.59
0.006
1.51E-07
<1E-12
9.29E-04
Table 3. Statistical analysis of the recorded direction of mousing jumps with regard to the season of the
year.
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Figure 2. Angular data revealing the NE alignment of mousing foxes independently of the season of the
year. The direction of the arrow represents the mean vector of angular data (µ), length of the arrow represents the r-value (length of the mean vector), and inner circles indicate the 0.05-level of significance.
Each triangle represents one or 2 (in the case of summer and autumn) observations.
(6) In conclusion: We have observed several dozens of different foxes of both sexes of different age
hunting different species of voles, mice, and moles at diverse localities in diverse habitats at different
times of the day at diverse weather conditions at diverse seasons of the year. This fact per se is evidence
that there cannot be a common environmental denominator for a certain prevalent jumping direction.
(7) The mean vector (about 40°) of body orientation of mousing foxes deviates systematically (unidirectionally) from geomagnetic North. The deviation of successful jumps is just about 20° and within the 95%
confidence interval (348°-341.4°). However, such deviations of a spontaneous "magnetic preference for
the North-South direction" from the actual N-S axis are well documented also for other mammals and in
other contexts, e.g. for ruminants (Begall et al. 2008), rodents (Burda et al. 1990), and bats (Wang et al.
2007). This phenomenon, supported now by a consistent finding in a carnivore is worth of investigation.
(8) References
Begall, S., Cerveny, J., Neef, J., Vojtech, O. & Burda, H. 2008 Magnetic alignment in grazing and resting
cattle and deer. PNAS USA 105, 13451-13455.
Burda, H., Marhold, S., Westenberger, T., Wiltschko, W. & Wiltschko, R. 1990 Magnetic compass orientation in the subterranean rodent Cryptomys hottentotus (Bathyergidae, Rodentia). Experientia 46,
528-530.
Phillips, J.B., Muheim, R. & Jorge, P.E. 2010 A behavioral perspective on the biophysics of the lightdependent magnetic compass: a link between directional and spatial perception? J. Exper. Biol.
213, 3247-3255.
Ritz, T., Adem, S. & Schulten, K. 2000 A model for photoreceptor based magnetoreception in birds. Biophys. J. 78, 707–718.
Solov'yov, I.A., Mouritsen, H., Schulten, K. 2010 Acuity of a cryptochrome and vision-based magnetoreception system in birds. Biophys. J. 99, 40-49.
Wang, Y., Pan, Y., Parsons, S., Walker, M. & Zhang, S. 2007 Bats respond to polarity of a magnetic
field. Proc. R. Soc. B 274, 2901-2905.
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(9) Hypothetical principle of a "magnetic range-finder" in the red fox assuming radical-pair-based
magnetoreception.
Figure 3. Hypothetical principle of a "magnetic range-finder" in the red fox assuming radical-pair-based
magnetoreception. (Based on a model by Phillips et al. 2010; and Phillips and Painter, personal communication.)
Upper row: Visual perception of a landscape with a hypothetical pattern generated by the light-dependent
magnetic compass (Ritz et al. 2000) superimposed in front of a fox heading northwards. Note that the visual pattern may be much more complex (cf., Ritz et al. 2000, Phillips et al. 2010, Solov'yov et al. 2010)
and will depend in part on the alignment of the light-absorbing molecules (cryptochromes?) in the photoreceptors; location of the sound source generated by the prey is illustrated by a yellow four pointed star.
Middle row: Interior of the eye showing the gradual shift in the projection of the visual location of the
prey sounds (yellow four pointed star) as the fox approaches the sound source.
Lower row: A fox approaching the sound source. When the image of the landmark projected on the retina
appears as superimposed upon a specific component of the pattern produced by the geomagnetic field (see
middle row), the fox is at a fixed distance and jumps.