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Two cases of height-seeking behaviour in the Common Toad, Bufo bufo (Linnaeus, 1758), in Denmark

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Two cases of Bufo bufo climbing vegetation in Denmark (Jutland) are reported. One small B. bufo was observed among the yellow flowers in the inflorescence of a European Goldenrod, Solidago virgaurea, at night. In the other case, two toads were found perching in a young Norway Spruce, Picea abies, during the day. These observations are compared with several published records of B. bufo and other members of the B. bufo complex. In a considerable number of published reports, individuals have been observed climbing trees and using holes and crevices, presumably for sheltering and/or foraging. Toads were seen climbing walls and a hedge and even utilizing birds’ nests probably for the same purposes. As to the two new observations, the individual observed in the flowers of European Goldenrod was probably predating upon invertebrate prey that was attracted by the flowers. Apparently, the observation of B. bufo climbing flowers constitutes a novel behavioural trait. It is speculated that the two individuals having climbed a young Norway Spruce might have been exploring the tree for holes that could be used for sheltering and they were possibly foraging in the tree at the same time. It is concluded that the occasional arboreal habits of B. bufo should be considered when surveys of the species are conducted outside the breeding season.
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©  Deutsche Gesellscha für Herpetologie und Terrarienkunde e.V. (DGHT), Mannheim, Germany
Two cases of height-seeking behaviour in the Common Toad,
Bufo bufo (L, ), in Denmark
H B
Abstract. Two cases of Bufo bufo climbing vegetation in Denmark (Jutland) are reported. One small B.
bufo was observed among the yellow owers in the inorescence of a European Goldenrod, Solidago
virgaurea, at night. In the other case, two toads were found perching in a young Norway Spruce, Picea
abies, during the day. ese observations are compared with several published records of B. bufo and
other members of the B. bufo complex. In a considerable number of published reports, individuals have
been observed climbing trees and using holes and crevices, presumably for sheltering and/or foraging.
Toads were seen climbing walls and a hedge and even utilizing birds’ nests probably for the same pur-
poses. As to the two new observations, the individual observed in the owers of European Goldenrod
was probably predating upon invertebrate prey that was attracted by the owers. Apparently, the ob-
servation of B. bufo climbing owers constitutes a novel behavioural trait. It is speculated that the two
individuals having climbed a young Norway Spruce might have been exploring the tree for holes that
could be used for sheltering and they were possibly foraging in the tree at the same time. It is concluded
that the occasional arboreal habits of B. bufo should be considered when surveys of the species are con-
ducted outside the breeding season.
Key words. Amphibia, Anura, Bufonidae, Bufo bufo, height-seeking, climbing, arboreal, height, behav-
iour, Denmark.
Zwei Fälle von Kletterverhalten der Erdkröte, Bufo bufo (L, ), in Dänemark
Zusammenfassung. Zwei Fälle von in der Vegetation kletternden Bufo bufo werden aus Dänemark
(Jütland) beschrieben. Ein Jungtier von B. bufo wurde nachts an der Spitze des gelben Blütenstandes
der Gewöhnlichen Goldrute, Solidago virgaurea, beobachtet. Im anderen Fall wurden zwei Kröten am
Tage in einem jüngeren Baum der Gemeinen Fichte, Picea abies, gefunden. Vergleiche zu publizierten
Beobachtungen bei Bufo bufo und des B. bufo-Komplexes werden vorgenommen. Der überwiegende
Teil der Publikationen bezieht sich auf Individuen in Baumhöhlungen, die als Versteckplätze und/oder
zur Nahrungssuche aufgesucht wurden. Kröten erklommen Wände sowie eine Hecke und suchten auch
Vogelnester – vermutlich zum gleichen Zweck – auf. Das Jungtier nutzte vermutlich die Lockwirkung
des Blütenstandes der Gewöhnlichen Goldrute auf unterschiedliche Wirbellose zur Nahrungsaufnah-
me; ein hier erstmals beschriebenes Verhalten. Die beiden in einer Gemeinen Fichte kletternden Tiere
waren wahrscheinlich auf der Suche nach Versteckplätzen bzw. nach Nahrung. Um die Art außerhalb
der Fortpanzungszeit nachzuweisen, sollte auch das gelegentliche Kletterverhalten von B. bufo in Be-
tracht gezogen werden.
Schlüsselwörter. Amphibia, Anura, Bufonidae, Bufo bufo, Aufenthalt in Höhen, Klettern, Verhalten,
Dänemark.
Introduction
Among Western Palaearctic anurans the only truly arbo-
real species are tree frogs of the genus Hyla. Other species
only exhibit climbing habits occasionally or exceptional-
ly. Consequently we tend to search solely around ground
level when working with such non-arboreal species. How-
ever, sometimes we may overlook individuals which devi-
ate from that general rule by climbing vegetation and other
elevated objects. In this report two cases of height-seeking
in the Common Toad, Bufo bufo, from Denmark are pre-
sented and documented with photos. ey are compared
with published records of height-seeking in that species.
Both observations were made in August .
Observations
Observer: H D
Locality: Bærslund,  km south of Herning, central
Jutland, western Denmark.
Date and time: – August , from : to : h.
Habitat: Cultivated area around a scout hut with open
lawns, surrounded by mixed forest. ere were also
areas of tall grass and herbaceous vegetation.
MERTENSIELLA  – . .  ISBN ––––
147
Fig. : A young Bufo bufo, SVL approx.  mm, among the owers in the inorescence of a European Goldenrod, Solidago
virgaurea, at a height of – cm at night. / Abb. : Jungtier von Bufo bufo mit ca.  mm KRL, nachts in einem Blütenstand
der Gewöhnlichen Goldrute, Solidago virgaurea, in ca. – cm Höhe. Photo / Foto: H. D.
Fig. : Two individuals of Bufo bufo perched on branches of a young Norway Spruce, Picea abies, during daytime. One toad
is clearly visible whereas the other is almost completely concealed by the trunk to the right of the rst one. / Abb. : Zwei In-
dividuen von Bufo bufo am Tage auf den Zweigen eines Jungbaumes der Gemeinen Fichte, Picea abies. Eine Kröte ist deutlich
sichtbar, während sich die zweite, nahezu gänzlich vom Stamm verdeckt, rechts neben der ersten bendet.
Photo / Foto: L. J. G.
Two cases of height-seeking behaviour in the Common Toad, Bufo bufo (L, ), in Denmark
148
Observation: During one night of eld work with
moths one young Bufo bufo, SVL approx.  mm, was
observed among the yellow owers in the top of a Eu-
ropean goldenrod, Solidago virgaurea, at a height of –
cm above the ground. e toad was photographed
immediately which took place at : h and some mi-
nutes later. e observer returned to the spot later and
the toad was still perched in the top of the plant. e
last observation was made at : h; yet another photo
was taken. e night was very humid and foggy and all
vegetation was wet with dew. Next morning at approx.
: h. the observer visited that particular place again.
However, the toad was not there any more (Fig. ).
During that night Lissotriton vulgaris and Rana tem-
poraria were also recorded at that locality.
Observer: L J G
Locality: Lystrup,  km northwest of Bryrup and km
south of Silkeborg, central Jutland, western Denmark.
Date and time:  August , at : h.
Habitat: A hill of pasture on sandy soil with several
young Norway Spruce, Picea abies, being approx.
cm tall.
Observation: e observer was going to cut down a
young Norway spruce of the above-mentioned height.
As the small branches were to be cut rst, one Bufo bufo,
SVL approx. – mm, was seen on a small branch
close to the trunk at a height of approx.  cm above the
ground. Right behind it there was a second individual of
unknown length (Figs.  and ).
e weather was dry and somewhat sunny, air tem-
perature approx. – ºC.
During that particular day G cut down ap-
prox.  individuals of Norway Spruce, but no other
toads were found. Previously he has cut down in total
more than , spruces without having noticed any
climbing toads.
ere was no birds nest in the spruce that was inhab-
ited by the two toads.
In general the observer has found many spiders and
harvestmen in spruces (mainly in the top), to a lesser
extent also other invertebrates like woodlice.
Discussion
Height-seeking among ground-dwelling amphibians is
a neglected behavioural trait as I have previously no-
ticed in the abundant and widespread Smooth Newt,
Lissotriton vulgaris (B ). Among reptiles
such traits are oen not paid much attention in Natrix
natrix though the species may in fact climb vegetation
now and then (B & A in press). ere
are a few published reports on climbing habits in Bufo
bufo although this species is also widespread and abun-
dant in Europe.
B. bufo is in general a laborious climber which can
overcome many obstacles on its way (S ). Espe-
cially during the spring migration to the breeding ponds
the ability to tackle obstacles like walls becomes obvi-
ous (B ). Smooth vertical surfaces pose seri-
ous challenges to the toads which have found expression
in a study by MI & R () who tried to solve
the problem of toads being trapped in gully pots. It was
concluded that the toads were able to escape through
“ladders” which consisted of perforated steel plates and
which were placed vertically or nearly vertically inside
these roadside drains. Judging from the illustrations
their height might have been approx. – cm.
In the following two reports individuals of climbing
B. bufo were situated in holes in trees. In Germany toads
were found hiding in holes and tree forks in Goat Wil-
low (Salix caprea) and Common Hazel (Corylus avella-
na) in heights between  cm and  cm (K et al.
). Moreover S () found one individual in
the hole of an old apple tree (Malus domesticus) which
Great Tits (Parus major) had been using as nest. at
was in a height of  cm above the ground.
Now and then B. bufo may also climb vertical or near-
ly vertical structures of buildings and other man-made
constructions. In North Rhine-Westphalia, Germany,
P () photographed one individual partly
hidden on a horizontal wood beam placed on the outer
wall of a house just below the roof in a height of approx.
 cm. Inasmuch as the toad tried to hide in an elevat-
ed part of such a construction, this case may be consid-
ered a parallel to the above observations of individuals
climbing trees.
S () cited some old reports of climbing B.
bufo published from  through  as follows. One
toad had climbed a smooth wall up to a height of  feet
Fig. : e young Norway Spruce on which one of the toads is
visible at a height of approx.  cm. / Abb. : Der Jungbaum
einer Gemeinen Fichte, in dem eine der Kröten in ca.  cm
Höhe sichtbar ist. Photo / Foto: L. J. G.
H B
149
( cm) above the ground, tting its body into the angle
formed where two sides met; to raise itself to that point
it had apparently taken advantage of every slight projec-
tion on the bricks. In a second case a toad had chosen a
small sheltered platform of leaves in a privet hedge ap-
prox.  feet ( cm) above the ground where it had re-
mained in residence for several months. Eventually two
instances where toads had been found in bird’s nests
were mentioned: One had been living for some time in
a deserted nest whereas another toad had been found in
the nest of a chanch.
In the Navarra province of northern Spain, G
() found impressive numbers of toads having
climbed oak trees (Quercus sp.).  individuals were
recorded in heights of an average of  cm, maximum
 cm. e author believed that they might have been
searching for moisture on the epiphytic moss colonising
the tree bark. In summer many toads were also utilis-
ing buttress (or tabular) roots of old oak trees. On the
Iberian Peninsula up to southern and western France
the B. bufo complex is represented by the taxon spinosus
which is now considered a distinct species, B. spinosus
(G ).
One important purpose of common toads climbing
trees is probably to make use of holes and other cavities
as hiding places. Moreover, foraging on and in trees may
also be an important factor. e abundance of woodlice
(families Porcellionidae and Philosciidae) occurring on
live and dead trees will oer excellent feeding opportu-
nities for toads which are utilising holes in trees as hi-
ding places because the wood in the holes is generally in
a process of decay. In a study in the northern outskirts
of Copenhagen it was observed that B. bufo oen for-
ages on woodlice, Porcellio scaber, on and around trees,
either at the foot of live trees or pieces of trunks of felled
trees (J ).
Apparently Gs observation of two com-
mon toads perched in a quite small spruce tree cannot
be directly associated with toads seeking out holes, cre-
vices or bird’s nests for hiding. However, potentially
they might have been exploring the tree for such hiding
places. It is also possible that feeding in the tree proved
benecial for the two toads.
e other observation of height-seeking B. bufo,
i.e. Ds observation on one small B. bufo having
climbed the inorescence of a European Goldenrod at
night, apparently constitutes a novel behavioural trait as
I have not been able to nd any record of B. bufo climb-
ing owers. I nd it likely that the main purpose was to
feed on invertebrate prey which had been attracted by
the owers.
e observations presented in this paper provide a
reminder of the occasional arboreal habits of B. bufo,
which must be considered when surveying for the spe-
cies outside the breeding season. It is recommended that
future observations of arboreal activities should be re-
corded eectively to further knowledge of the behaviour
of this species.
Acknowledgements
I am very grateful to H D (Herning, Den-
mark) and L J G (Bryrup, Den-
mark) for making their observations available to me for
this paper. U S (Naturkundemuseum Er-
furt, Germany) kindly provided literature.
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(L, ) climbing tree to a height of  cm.
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obstetricians (Midwife Toad), and Rana temporaria
(Common Frog). Tree Climbing. – Herpetological
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ladders within roadside gullypots in Angus, Scotland:
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Author
H B, Irisvej ,  Køge (Denmark),
E-Mail: bringsoe@email.dk
Two cases of height-seeking behaviour in the Common Toad, Bufo bufo (L, ), in Denmark
... Temperate region toads could be considered archetypal terrestrial amphibians and while there are some literature mentions of arboreal habits, these are usually accidental observations of 1-2 individuals [12]. These observations include the common toad Bufo bufo in Europe, one of the most widespread and common amphibians in Europe, which inhabits most of the continent, from the west coast of Britain to eastern Siberia and Kazakhstan [13]. ...
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Alytes obstetricians (Midwife Toad), and Rana temporaria (Common Frog). Tree Climbing
  • A Gosá
Gosá, A. (): Bufo bufo (Common Toad), Alytes obstetricians (Midwife Toad), and Rana temporaria (Common Frog). Tree Climbing. -Herpetological Review, : .
Aastrup (in press): Natrix natrix (Linnaeus, ) climbing tree to a height of  cm
  • H Bringsøe
Bringsøe, H. & P. Aastrup (in press): Natrix natrix (Linnaeus, ) climbing tree to a height of  cm. – Herpetozoa, .
): Skrubtudsens (Bufo bufo) aktivitet i naturen
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