T H E E M I R AT E S – A N AT U R A L H I S T O R Y
AMPHIBIANS
AMPHIBIANS
AMPHIBIANS (CLASS AMPHIBIA) COMPRISE frogs, toads, newts, salamanders and caecilians. Some 5,400 species are
currently recognised worldwide. Most amphibians must lay their eggs in fresh water, where the juvenile or larval
stage develops. In addition, the skin of most amphibians provides little protection against drying out. For this
reason, the majority of them live in or near ponds, streams or other moist places. Some, however, have adapted to
more arid or seasonal environments. In the Arabian Peninsula, only frogs and toads (order Anura) are present and
nine species are known, of which six are endemic (i.e. found only in Arabia) (Arnold 1980a; Balletto et al. 1985).
In the UAE, the only amphibians are two similar species of toad,
been found in traditional stone-lined cisterns in Ru’us al-Jibal
the Arabian toad Bufo arabicus (formerly called B. orientalis) and
mountain settlements. Their distribution suggests that they must
the Dhofar toad B. dhufarensis. Their natural distribution is in the
be able to breed successfully even in puddles and potholes away
mountain regions and in oases on the surrounding gravel plains,
from major watercourses. In the wetter Dhofar region of Oman,
although in recent times they have been introduced into at least
where the Dhofar toad is also the only toad species present, it is
a few man-made environments elsewhere. Both toads are also
reported to be more active by day and is usually found near water.
found in Oman, Yemen and western Saudi Arabia. Prior reports
This suggests that its behaviour and ecology in most of the UAE
of B. arabicus from Jordan have not been confirmed and all toads
have had to accommodate the presence of the Arabian toad,
there are now considered to represent B. viridis, the green toad, a
which appears to dominate the daytime wadi pool environment
widespread and highly adaptable species that ranges across most
(Arnold 1980a).
of the Palaeartic (Disi 2002).
The Arabian toad is by far the most commonly seen toad in the
In or near permanent water, breeding occurs year round, as
shown by the presence of black, pearl-like strings of toad eggs in
mountain wadis of the UAE. They are normally found in or near
rocky pools, cisterns and falaj channels. In more extreme habitats,
water and are active by day as well as by night, although they often
tadpoles must develop rapidly and adult toads may be active for
seek shelter from direct sunlight in the heat of the day. Close
only a brief period after rain, when they breed.
inspection of mountain pools frequently reveals well-camouflaged
The strategy of both UAE toad species is to lay large numbers of
toads, often clustered in damp or shady crannies. When other
eggs, on the chance that at least a couple will reach adulthood and
shelter is scarce, they may excavate small hollows in damp wadi
breed again. Tens of thousands of Dhofar toadlets were present
gravel, resembling donkey hoof prints, perhaps to take advantage
behind the Tawiyan Dam on the southern edge of the Ru’us al-Jibal
of a slightly cooler or more humid microclimate.
for several months following spring rain in 2003. By day they took
The Arabian toad is absent, nevertheless, from the Ru’us al-Jibal
shelter along the shoreline, among rocks or within the cracks
in the north of the Hajar Mountains and also from Dhofar in
formed in the drying silt around the perimeter of the temporary
southern Oman. This isolated distribution leaves open the
reservoir, emerging like a plague at the footfalls of a human
possibility that the Arabian toad of the UAE and Oman will prove
observer. By night they perched to feed on insects.
to be genetically distinct from the Arabian toad of western Arabia,
although both are undoubtedly related to the B. viridis populations
Dhofar toad Bufo dhufarensis
to the north.
The Dhofar toad is less commonly encountered in the
UAE, partly because adults are primarily nocturnal and
partly because its usual habitat seems to be at some
distance from water bodies. It is, however, the only toad
species found within the mountains of the Ru’us al-Jibal, where
permanent water is extremely scarce, and it has been found there
on one of the highest ridges in the UAE, at an elevation above
1,500 metres (Cunningham and Feulner 2001). A mating frenzy of
Dhofar toads was observed by day in temporary pools in a
boulder-strewn wadi in the Ru’us al-Jibal, a few days after
winter rain in early 2001, and more than 500 tadpoles
were present in the pools that remained about five
weeks later. Dhofar toads and tadpoles have also
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T H E E M I R AT E S – A N AT U R A L H I S T O R Y
ground for more than ten minutes, vigorously rubbing its snout to
purge the sensation (Jongbloed 2000).
The normal diet of the local toads is insects, which they catch,
like other frogs and toads, by means of a sticky and prehensile
tongue. Cannibalism has been documented in the Arabian toad,
larger toads consuming small juveniles (Gross and Shepley 1994).
They are also reported to eat wadi fish trapped in drying puddles.
Toads have no teeth and cannot chew, so they must swallow even
large prey items whole.
The Arabian and Dhofar toads are very similar in appearance.
Both show considerable and overlapping variation in colour, from
green to tan to brown (and even grey) and from mottled to
Except perhaps when aestivating, both the Arabian toad and the
Dhofar toad emerge rapidly in response to rain or even drizzle,
like most toads everywhere. In the wadi environment, at such times
dozens of toads may be visible at any point along the gravel wadi
bed. Another species that emerges with them under these conditions
is the carpet viper Echis omanensis (formerly E coloratus), a resident
of the lower mountains that, in the UAE, appears to prey largely on
toads. Other local toad predators include Brandt’s hedgehog
Paraechinus hypomelas and the wadi racer Coluber rhodorhachis, a
long thin snake that also preys on tadpoles.
Most toads are unpalatable to potential predators because their
monochrome, although the most vividly spotted toads are almost
invariably Arabian toads. Size is likewise similar and overlapping,
with adult females of both species being larger than the
corresponding males. The Dhofar toad is said to be the smaller of
the two species (Balletto et al. 1985) but some of the largest
skin secretes chemicals that may range from noxious to deadly.
This is especially true of Bufo species, but the native UAE predators
have apparently become immune to the secretions of the local
toads. By contrast, a frisky domestic dog that tried to take
a local toad is reported to have dropped it
immediately, foamed at the mouth
and rolled about on the
toads the authors have observed have been Dhofar toads. The
Dhofar toad has a somewhat flatter body shape, but this is a
feature that is often difficult to judge confidently.
The two species can be reliably distinguished, however, by
careful attention to several features:
(1) The tympanum or eardrum. The tympanum of the Dhofar toad is
large and prominent. It is nearly the same diameter as the eye,
has a distinct raised border, and nearly abuts the edge of the eye
socket. The tympanum of the Arabian toad is smaller (only
about half or two-thirds the diameter of the eye), is set back
from the eye socket at a distance almost equal to the diameter
of the tympanum itself, and the margin is often indistinct, so
that the tympanum can be difficult to recognise, especially if
AMPHIBIANS
Both toads have the ability to aestivate in a dormant state in
mud, gravel, or rock crevices and are able to do so for as much as
three years or more if necessary (Balletto et al. 1985; Schätti and
Gasperetti 1994). Such a lifestyle is consistent with the ecology of
the so-called ‘rain frogs’ of arid environments elsewhere. It has
been estimated that even a single opportunity to feast, for example
on a termite swarm, would allow a toad to survive in a dormant
state for a year or more. In Jordan, the related green toad is known
to accommodate dehydration by tolerating high concentrations of
urea and blood plasma. It has also been shown to seek refuge in
rodent burrows, where the humidity is substantially higher than
outside (Disi 2002).
(2) The dorsal profile of the snout. The dorsal profile of the Dhofar
toad’s snout is a distinct and steep-sided trapezoid, and the
eyeballs are slightly more prominent. In the Arabian toad, the
dorsal profile of the snout is somewhat more rounded. This
distinction correlates with a broader nasal bridge and more
vertical ‘cheeks’ in the Dhofar toad, whereas the ‘cheeks’ of
the Arabian toad slope outward from a narrower nasal bridge.
(3) The lateral profile of the snout. The front edge of the snout of
the Arabian toad is vertical or rounded in profile, whereas the
snout of the Dhofar toad slopes backwards from the tip, just
below the nostrils, to the lower jaw.
(4) The mating call. The staccato kra-kra-kra mating call of the
Dhofar toad is readily distinguishable from the prolonged
krrraaaa of the Arabian toad, which has been likened to the
creaking of a hinge.
These same features are often discernible in juvenile toads and,
in fact, young Dhofar toads seem to be somewhat more uniform
in appearance than adults, independent of where in the UAE they
are found, having a pale cocoa brown colour with black mottling,
and a dark horizontal eye stripe.
It has sometimes been said in the UAE that Dhofar toads can be
distinguished by their black toe tips, but in fact the local Arabian
toads sometimes also have black or brown
toe tips, although it seems that normally
the tips are white. In any case
this feature is limited to
the most distal extremity
and is usually difficult to
observe confidently unless
the toad has been caught.
the toad is well mottled.
Tadpoles of the two species can also be distinguished, based on
the configuration of the mouth elements, the colouration and
attachment of the caudal (tail) fin, and the visibility of the
intestines (Balletto et al. 1985).
Amphibian populations are generally in decline worldwide for
reasons that are not yet well understood, although various factors
such as global warming, acid rain, water pollution, fungal infections
and insecticides have been mentioned as possible causes. Observed
toad numbers in the UAE are highly susceptible to short-term
environmental conditions, principally drought, and no evidence
exists of longer-term trends. In view of the general concern,
however, ecological study and monitoring of the two UAE toads,
including attention to their ecology, population dynamics,
niche separation and the effects of land use and
urban growth, would be of value.
Peter Cunningham and Gary Feulner
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Dhofar toad Bufo dhufarensis
ABOVE AND RIGHT:
Arabian toad
Bufo arabicus
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