This paper has been reproduced with the permission of the
Durrell Wildlife Conservation Trust, being originally published in Dodo,
Journal of the Wildlife Preservation Trust, 34: pp. 103-114. 1998.© Jersey
Wildlife Preservation Trust
THE CAPTIVE MANAGEMENT AND
BREEDING OF POISON-DART FROGS, FAMILY DENDROBATIDAE, AT JERSEY WILDLIFE
PRESERVATION TRUST, USING A PILOT SPECIES
By DONNA J. PREECE
Herpetology Department, Jersey Wildlife
Preservation Trust.
ABSTRACT:
The Jersey Wildlife Preservation Trust (JWPT)
started work with the green and black poison-dart frog Dendrobates auratus
in 1994. The acquisition of this species of Dendrobatid, for use as a model
species, was in direct response to the initiation by Edinburgh Zoo of a
Federation of Zoological Gardens of Great Britain and Ireland Joint Management
of Species Programme for the endangered blue poison-dart frog, D. azureus.
D. auratus, a relatively common and widely kept poison-dart frog, was
used as a pilot species as staff in the JWPT Gaherty Reptile and Amphibian
Conservation Centre had no prior experience in the management of Dendrobatid
frogs. Following considerable success and experimentation with the model
species, the target species, D. azureus, was added to the collection in
1995. This rare species proved relatively straightforward to maintain and breed,
building on the knowledge and skills gained during the previous year with D.
auratus. The expertise developed in maintaining and managing these two
species of poison-dart frog has equipped us for future management of other
members of the family Dendrobatidae and similar species.
KEYWORDS: poison-dart frog, Dendrobatidae, model
species, husbandry, studbook, managed programme.
Introduction
There are currently about 170 described species of frog in the family
Dendrobatidae (Barnett, 1997). The
distribution of the poison-dart frog family extends from Nicaragua in Central
America, south to the limits of the rainforest in South America, which forms a
line running through Peru to the Bolivia-Paraguay border (Duellman
and Trueb, 1994).
The family can be divided into at
least eight genera, Allobates, Aromobates, Colostethus, Dendrobates,
Epipedobates, Minyobates, Phobobates and Phyllobates (Duellman,
1993). The morphological characters used to differentiate between species of
Dendrobatidae are mainly internal and include distinguishing features of the
skeleton and muscular system. Many species are brightly coloured, particularly
those in the genera Dendrobates and Phyllobates, but an equal
number, notably the extensive genus Colostethus, are predominantly rather
dull. Dendrobatid frogs range in size from the
largest, 6 cm long species such as Dendrobates tinctorius, Phyllobates
terribilis, and the only Aromobates, Aromobates nocturnus (Myers
et al., 1991), to the tiny Minyobates minutus which reaches
little more than 1 cm in length.
The common names frequently
used for the family, poison-dart or poison-arrow frogs, or sometimes simply dart
frogs, originate from the Choco Indians of Colombia. They use a small number of
species in the genus Phyllobates for the tipping of hunting darts (Myers
et al, 1978). The three species used by the Indians, P.
terribilis, P. bicolor and P. aurotaenia, produce a variety of
skin secretions including batrachotoxin, one of the most toxic substances known.
This group of lethal nerve toxins, although fatal in tiny amounts if they reach
the blood stream, appear to be relatively harmless if ingested from the body of
a dead animal (Myers et al., 1978). The Choco
Indians remove the area of flesh directly surrounding the dart puncture and
consume the remainder of the carcass (Moffett,
1995).
The rest of the Dendrobatid
frogs have inherited their common name from these few frighteningly toxic frogs.
Approximately 50% of the family are thought to produce toxins of varying
strengths (Zimmerman, 1989), and these
frogs often display bright colours. Most of these species belong to the genera Dendrobates
and Phyllobates and are a good example of aposematic
colouration. The remaining species do not produce any toxins, and therefore
rely on secretive behaviour and cryptic coloration for protection. These frogs
are mostly in the genus Colostethus (Walls,
1994b).
All dendrobatids are
generally diurnal. Their habitat is usually restricted to warm, humid forests,
where they can be found on or near the ground, often close to small pools and
streams. Several species, however, prefer to live in the humid habitats that can
be found several metres up amongst the epiphytic mosses, bromeliads and ferns
(Walls, 1994b).
In many species males defend small territories, often just a
leaf or a stone. They advertise the ownership of these areas by calling. Some of
these calls are no more than chirps or buzzes and often cannot be heard by the
human ear. Others, such as the calls produced by many species of Phyllobates,
are loud trilling calls that carry for some distance. The
call to attract a female is different from that used to announce territory
ownership, and males may call for many hours in attempt to attract a receptive
female (Hesselhaus, 1992). Once the female
has approached she will often attempt to stroke his head or back with her front
feet, a behaviour that may last for several hours. Eventually the male will
attempt to lead the female to an area that he has determined suitable for egg
deposition. This is normally a leaf or flat surface on or near the ground, which
the male has "cleaned". If the female deems the site suitable and is
receptive, she will lay the clutch of eggs, varying from two to several dozen
depending upon species. In some cases the females will not lay the whole clutch
at once, but may go on to lay batches of the clutch with several different
males, thereby increasing the chance of her eggs being well maintained. Fertilisation
by the male does not always take place immediately (Mattison,
1982, 1993).
In most species, the male is responsible for the care of the
eggs during development, and he visits them at regular intervals to moisten them
with liquid from his bladder and protect them from fungal infection or
predation. As soon as the larvae are ready to hatch, usually at 10-20 days (R.
Gibson, pers. comm.) the parent providing care sits upon the egg mass and waits
for one or more tadpoles to climb up on its back for transportation to a
suitable water body.
Tadpoles tend to fall into three types. Those that have heavy
beaks with strong serrations are carnivorous, feeding on mosquito larvae and
other tadpoles. Others have weaker beaks and tend to feed on detritus of varying
types, including algae and organic debris. A third type, which includes species
related to Dendrobates histrionicus and D. pumilio, require
unfertilised eggs, which are called food eggs, for complete development. In
these species it is the female that provides parental care to the egg mass and
subsequently the larvae. Every few days, until metamorphosis, the female visits
the sites where she placed individual larvae and lays one or more infertile eggs
to feed the tadpole.
Metamorphosis usually
takes place after two to three months in the water body, but there is much
variation within and beyond this time band (Zimmerman,
1986). The dorsal coloration of the tadpoles will normally begin to develop
with the extension of the hind limbs. Coloration and pattern continue to develop
as the forelimbs are grown and the tail re-absorbed, and upon metamorphosis many
poison-dart frogs are miniature replicas of their parents in appearance.
This paper describes the management of two species of
poison-dart frog, Dendrobates auratus and D. azureus. D.
auratus was used as a pilot species to develop management techniques for the
endangered D. azureus.
Management of the green and black poison-dart
frog Dendrobates auratus
Background
In April 1994, four sub adult green and black poison-dart frogs Dendrobates
auratus, and six tadpoles, were imported to the Jersey Wildlife Preservation
Trust (JWPT) from Edinburgh Zoo (Blake and Sherriff, 1997). All of the
individuals were captive bred at Edinburgh Zoo and of at least second or third
generation in captivity. This species was selected as a model species by JWPT to
allow the herpetology staff to develop and refine the husbandry techniques
necessary to maintain and breed Dendrobatid frogs successfully in captivity.
These techniques could then be applied to the much rarer target species, D.
azureus, the blue poison-dart frog.
Description
Dendrobates auratus is a diurnal, brightly coloured,
slightly toxic frog, which is now recognised as occurring in several colour
forms. It has a fairly large geographical range, which extends from Nicaragua to
Panama, and into northwestern Colombia. The most widely seen colour form is
black and green; these frogs have bands and blotches of bright metallic green on
a black background, but the proportion of each colour is highly variable. They
grow to approximately 4.5 cm in length with both larger and smaller individuals
being found.
Sexual dimorphism becomes apparent at approximately 12-14
months of age. The front fingers of the male develop a flat, bi-lobed, terminal
disc. Occasionally an impression of a throat sac can be seen, but this
particular species is not very vocal, the only sound produced being a low
pitched 'buzzing'. Males are, on average, more slightly built than females,
which become particularly rotund when gravid.
Each frog has its own unique pattern of bands and blotches.
This makes the identification of individuals easy, as both photographic and
diagrammatic records can be kept. Due to the relative ease of management of this
species in captivity, the green and black poison-dart frog has become a popular
species in zoological collections as well as with hobbyists.
Accommodation and environmental parameters
A purpose-built enclosure was constructed in the exhibition area of the Gaherty
Reptile and Amphibian Conservation Centre (GRACC) at JWPT. This vivarium
consists of a deep brickwork base, filled with coarse gravel for drainage and
topped with compost and bark chippings for planting, on which an all-glass
construction is fitted. The interior dimensions of the vivarium are
approximately 2.5 m long x 1.5 m wide x 1.0 m high. Two hinged doors provide
keeper access, one on either side. The enclosure is landscaped, with a variety
of natural substrates, numerous branches, rocks and caves. At one end there is a
rock face down which a waterfall flows. The water then runs through the middle
of the enclosure and into a collection pool, where a simple aquarium pump sends
it back to the waterfall. The vivarium is densely planted with a variety of
plants, including Scindapsus "Marble Queen", Scindapsus
aureus, Ficus pumila, Maranta sp., Caladium sp., Aechmea
fasciata, Guzmania lingulata and several species of Cymbidium.
Within the enclosure several areas are kept clear of vegetation, as very densely
planted areas have been shown to inhibit feeding, leading to thin undernourished
frogs (R. Gibson, pers. comm.). The plants are watered each morning, and this
regime, coupled with the permanent water in the pool system, provides a
consistently high but varied humidity throughout the enclosure.
The natural habitat of Dendrobates
auratus experiences only minor variations in photoperiod and temperatures
during the year (Walls, 1994b). The temperature of the D. auratus
enclosure remains virtually constant throughout the year, being on an average
2-3°C lower in the winter. Daytime ambient temperatures are about 26-27°C,
night-time temperatures dropping to approximately 22°C. As a consequence of
being well planted, humidity is kept relatively high, varying from 70-90 %
throughout the enclosure all year round.
Two large, metal-halide, floodlights are suspended 1.5 m above
the vivarium floor. These lights are operated on a 10/14 hour day/night
photoperiod and provide a broad spectrum light suitable for plant growth. The
ambient lighting in the building is based on Madagascar dawn and dusk times. On
the longest day, 22 June, it is illuminated for 13.5 hours, while on the
shortest day, 23 December, it is reduced to 11.5 hours. Every two weeks a change
of five minutes at both ends of the daylight period allows for the gradual
increase and decrease of the photoperiod throughout the year.
Diet and feeding
To provide an adequate and regular food supply JWPT keeps its own insect room,
which holds two species of cricket, Acheta domestica and Gryllus bimaculatus,
and provides spaces for the rearing of fruit fly cultures. The cricket cultures
are harvested at appropriate stages for the whole of the reptile and amphibian
collection. The poison-dart frogs are fed on hatchling and juvenile crickets, up
to the size of 4 mm. Larger crickets are not eaten readily and may be ignored by
the frogs. Uneaten crickets will grow up in the vivarium and may cause
significant damage both to plants and frogs.
Two types of fruit fly, Drosophila spp., are maintained
for food, a vestigial-winged form and a giant, winged but non-flying form. The
flies are reared with alternate generations, on a homemade, vitamin enriched,
banana and porridge oat medium and a commercial Drosophila mix (Blades
Biological). Each culture continues to produce flies for up to six weeks. The
first, freshly hatched flies in a culture are removed to start new cultures. All
subsequent flies are used for food. Three times a week, all artificially
cultured insects are dusted with "Nutrobal" multivitamin and mineral
supplement.
In addition to the staple diet of crickets and fruit flies,
wild harvested invertebrates are used as much as possible during the summer.
This dietary supplementation with ants Lasius niger (which occur
naturally in the enclosure), aphids and meadow sweepings (which are collected by
the herpetology staff and volunteers), and the continual influx of invertebrates
introduced with fresh leaf, is considered very important for the long-term
health and reproductive vigour of the frog colony.
Newly metamorphosed frogs are fed on springtails Collembola,
which are cultured in bins containing moist, warm soil and humus and fed with
carrot and mushrooms. Frogs are fed 5-6 days per week, depending upon
development, and, as they are diurnal, are normally provided with food in the
morning giving the opportunity to forage all day.
Breeding
All four young frogs and all six tadpoles received from Edinburgh Zoo were
successfully reared to breeding age, following husbandry recommendations made by
Edinburgh Zoo staff (Blake and
Sherriff, 1997; Skelton, 1997). These 10
frogs, four males and six females, were housed together in the vivarium, sharing
it with a group of 10 stream frogs, Colostethus trinitatis.
Due to its dense planting, the enclosure provided many natural
oviposition sites, but several artificial sites were also provided. These took
the form of coconut shells cut in half and placed over a Petri-dish with an
artificial leaf or disc of plastic in the base. These artificial sites were kept
damp by spraying as part of the normal morning spraying routine. The first
oviposition from the young Edinburgh Zoo frogs occurred in November 1994, and
the first fertile eggs were produced in December 1994.
The frogs exhibited standard Dendrobatid courtship with both
females and males fighting to assume dominance. Within a large breeding group it
is advisable to have a higher number of males than females (the opposite of the
JWPT group structure) to ensure better brood care by males.
The eggs were normally removed from the enclosure for
intensive artificial rearing, but occasionally clutches were left in situ
to develop on their own. When a clutch of eggs was removed they were kept partly
covered in a Petri-dish at 23-27°C. Sufficient aged dechlorinated tap water was
added to the dish to ensure the eggs were kept moist, but not covered by the
water. Twice daily, water was dripped onto the eggs to mimic the action of the
natural parental brood care. Hatching occurred in 10-14 days at this
temperature.
Larval rearing
The first few clutches of tadpoles were reared individually with regular water
changes using aged tap water. As more experience was gained the volume of water
was increased, a gravel layer was added, which acted as a passive detritus
filter, and aquatic plants were added for cover and as a food source. This
manipulation was extended to the point at which water was never changed
throughout the development of the larvae. The gravel layer trapped any detritus,
and the aquatic plants provided natural water oxygenation. Water was
occasionally added to compensate for any evaporation. Throughout this time no
active filtration or artificial aeration was employed.
Further experimentation involved rearing up to 12 sibling
tadpoles in large volumes of water (1-2 litres). By providing them with a
constant and adequate food source and adequate hiding places, it was found that
they tended to take longer to metamorphose but did so at a larger size,
producing a stronger, more robust froglet at metamorphosis. Within such groups
there was great variation in the duration of tadpole development. The
"dominant" tadpoles developed within as little as 10 weeks, while the
"subordinate" tadpoles could take as long as 20 weeks or more. If an
adequate food source and sufficient refuges for each larva are provided, little
or no cannibalism occurs. Cannibalism was found to be more prevalent in
non-sibling groups, i.e. in larvae from more than one clutch.
The diet also underwent experimentation, with tropical fish
food being the original staple. Flaked, granular and stick fish foods were
alternated and small dead crickets, mealworm innards, cuttlefish bone, beef
heart, cooked mussel, Spirulina algae tablets, aquatic plants and natural
algae were all provided. This experimentation has resulted in the use of all
these foods for rearing tadpoles.
To reduce occurrences of
spindly leg, the tadpoles are illuminated by Reptisun 5.0 strip lights (Blatchford,
1986). However, tadpoles have been successfully reared without exposure to
any form of ultra-violet radiation. Breeding which takes place in the display
enclosure, with natural brood care, does so without exposure to artificial UV
sources and without supplementary feeding of tadpoles.
Metamorphosis and rearing of juveniles
Once front legs have emerged individual tadpoles are removed to larger
containers positioned on a slope to provide graduated water depth and dry land.
Vegetation is placed in both the water and the land to allow for footholds and
cover. Once 90% of the tail is reabsorbed they are removed to small (27 cm long
x 17 cm high x 19 cm wide), well ventilated, plastic vivaria furnished with a 2
cm deep moist compost substrate, several dry leaves for cover and a shallow
water dish. Most D. auratus at JWPT metamorphose between eight and 12
weeks.
Sibling groups of up to four
animals are kept in larger plastic vivaria (36 cm long x 21 cm high x 22 cm
wide) and Reptisun 2.0 strip lights are used for illumination. Up to 30 vivaria
are kept on a rack system and the temperature is controlled within the room by a
mobile air conditioner. Temperatures above 30°C, even for short periods of
time, may be lethal to frogs (Walls, 1994a),
and the temperature in the rearing room is maintained at 23-28°C. Each vivarium
is sprayed every morning with warm water, and feeding takes place before midday
while the frogs are at their most active. The relatively small size of the
vivaria keeps the young frogs in close proximity to their food source. The type
of food offered to recent metamorphs depends upon the size of the frogs. Dendrobates
auratus metamorphs are usually large enough to accept hatchling
(pin-head) crickets and vestigial-winged fruit flies but they are also offered a
constant supply of springtails. Careful observation of young frogs during
feeding ensures that any subordinate specimens not feeding well, or appearing
under weight, can be segregated and the situation remedied.
Breeding results
The first clutches of eggs were discovered in November 1994, with the first
fertile eggs in December 1994. This clutch produced five frogs. Ten infertile
clutches were located in the following few months before the next fertile clutch
was found in March 1995. From March 1995 onwards almost every clutch discovered
was fertile. Throughout 1995, 81 clutches of eggs were produced. Such high
productivity quickly led staff to discontinue active collection and rearing of
spawn and tadpoles and instead to remove and destroy all clutches found.
Inevitably, despite removing the favoured artificial spawning sites, occasional
clutches were undetected and developed through to metamorphosis in situ.
Noticeable variations in the number of eggs produced
throughout the year have been observed with a decrease in the number of clutches
occurring in the summer months when the temperature of the building is higher.
Summary
The breeding data compiled between the frogs’ arrival in April 1994 until
October 1998 (Tables I and II)
clearly demonstrate the highly fecund reproductive nature of this species in
captivity and serve to highlight the need to manage and control responsibly the
number of captive animals produced. All 10 D. auratus obtained from
Edinburgh in April 1994 are still alive (December 1998) and continue to produce
viable clutches of eggs. The success enjoyed with D. auratus, and the
valuable skills developed, allowed staff to transfer attention to the target
species, D. azureus.
Management of the blue
poison-dart frog Dendrobates azureus
Background
This species has a very limited distribution, only occurring within a few
isolated pockets in the Sipaliwini Savannah in the South of Surinam (Walls,
1994b). The blue poison-dart frogs' habitat consists of a number of forest
"islands" of relict rainforest at low elevations. These areas stand
out from the surrounding drier areas but are difficult to reach and survey
adequately. Although not listed in the 1994 IUCN Red List of Threatened
Animals, it is widely considered by herpetologists to be a highly endangered
species and undoubtedly one of the rarest in its family.
Edinburgh Zoo received a group of nine individuals from
Baltimore Aquarium in the USA in 1992. After success with this group of frogs
and the new success of Dendrobatid management at JWPT, Edinburgh Zoo initiated a
Federation of Zoological Gardens of Great Britain and Ireland Joint Management
of Species Programme (JMSP) studbook for the species and approached JWPT to
begin working with it. Three frogs, one male and two females, arrived in March
1995, another pair in June 1995, and a further two males in June 1996.
Description
Dendrobates azureus
was first described in 1969, by the Dutch herpetologist Hoogmoed (Hoogmoed,
1971). It ranges in adult body length from 3.8-5.0 cm. Mature males have
clearly defined, bi-lobed toe discs on the forefeet, and both sexes sit in a
characteristic hunchbacked position. The arms and legs are generally immaculate
deep blue and contrast with the paler blue sides and belly. The deep blue back
and dorsal surface of the head are patterned with very dark blue to black spots
in a pattern unique to each individual.
Accommodation, environmental parameters, diet
and feeding
A purpose-built enclosure was constructed in the public area of the GRACC. This
enclosure had the same components as the D. auratus enclosure described
above and was of similar dimensions. Daily spraying and feeding regimes are as
for D. auratus, as is the diet. Up to nine D. azureus have
successfully shared this enclosure. Temperature is maintained at between 22°C
and 27°C. This species is less tolerant of periods of high
temperature than D. auratus.
Breeding
Although courtship behaviour and egg deposition is regularly observed in the
display enclosure, natural breeding in a group seems to be less successful with
this species than with D. auratus. The first clutches of eggs were
discovered in August 1995, approximately three months after the first frogs
arrived. The first four clutches were infertile and several subsequent clutches
had fertile ova which failed to develop. These clutches were produced by young
sibling animals in the display vivarium, from which it was never intended to
breed. Males were often observed to be carrying tadpoles in the exhibit
enclosure but few tadpoles were observed and no froglets have been produced in
the display vivarium.
In order to breed this species successfully, and to fulfill
the studbook requirements for known parentage and controlled breeding, a
purpose-built breeding vivarium was used in the off-exhibit Dendrobatid rearing
room in the GRACC. A large glass vivarium (0.80 m long x 0.55 m deep x 0.6 m
high) was constructed with dense vegetation for security and high humidity and a
single artificial (coconut) spawning site. The pair of frogs required for
breeding was identified by the studbook keeper and the individuals introduced to
the breeding vivarium.
Several weeks are often required for a newly introduced pair
of D. azureus to settle and begin breeding. The failure to reproduce this
species successfully in other collections could well be due to insufficient time
being given to pairs for familiarisation with each other and their surroundings.
Breeding was
successfully initiated with the first pair of frogs in this enclosure
approximately two weeks after pairing. Heavy morning "rainfall"
provided with a handheld pressurised sprayer and permanently high humidity (90%)
stimulated the male to call, although it is the female of this species that
initiates courtship (Zimmerman
and Zimmerman, 1994). A receptive female approaches the male and strokes him
all over the body with her forelimbs. The male then normally leads the female to
a suitable spawning site.
Clutches normally contain between six and nine eggs. The eggs
are left in the enclosure until it is certain that the male has fertilised them,
or some development has occurred. The male in some pairings has been observed to
squirt liquid from his vent over the eggs in order to keep them moist and
oxygenated (R. Gibson, pers. comm.)
In most cases the eggs are removed from the enclosure after
24-48 hours. They are then partially covered and enough water added to just
touch the base of the clump of eggs, but not to cover them. They are kept at
22-27°C and checked twice a day, when water from a syringe is dribbled over the
eggs to mimic male brood care.
Larval rearing
The tadpoles normally emerge from the eggs after 12-16 days. Upon hatching each
tadpole is transferred to an individual water container, with a 1 cm layer of
small pea gravel in the bottom, a piece of aquatic vegetation for cover and
oxygenation, and a piece of cuttlefish bone. These water containers are then
exposed to a source of UV, in this case Reptisun 2.0 strip lights, until limb
budding begins, and Reptisun 5.0 thereafter. Tadpoles are fed the same diet as
that used with great success for D. auratus. Aquaria provide adequate
water volume to prevent the need for any water changes, except in rare cases
where the water has become excessively fouled due to over feeding. The water
levels are kept topped up by adding more dechlorinated water, which has been
left for 24 hr to reach the same temperature.
Trials with sibling groups of tadpoles proved unsuccessful.
This species is far more prone to cannibalism than D. auratus,
irrespective of aquarium volume, food supply and provision of refuges.
Metamorphosis and rearing of juveniles
The adult pattern begins to appear with the extension of the rear limbs. Once
the front legs have emerged, usually 3-6 weeks after the rear limbs, individual
tadpoles are removed to larger containers positioned on a slope as used for
D. auratus. When the tail has been reabsorbed they are removed to small
plastic vivaria, identical to those described for D. auratus juveniles.
All aspects of juvenile husbandry are identical to that used for D. auratus,
with one exception: the blue dart-frog juveniles showed a greater tendency for
subordinate individuals to do badly in large groups, and, as a result, this
species is never reared in groups of more than five.
Breeding results
The first clutches of fertile eggs were discovered in June 1996, with the first
viable eggs making it to hatching in August 1996. Since then JWPT has limited
its production according to the studbook requirements and has bred 23 D.
azureus (Tables III and IV).
Frogs bred in 1996-97, from the first studbook pairing, began to produce
clutches of fertile eggs in April 1998, indicating an age of 12 months to
maturity for captive-bred specimens.
Summary
Given adequate space, correct temperature variations and adequate lighting and
variety of diet, D. azureus is easily kept and bred in captivity. The
five original animals from Edinburgh Zoo are still alive (December 1998) and
continue to produce viable clutches within the exhibit enclosure. The oldest
individual, a male which originates from Baltimore Aquarium, is more than 12
years old.
All future breeding will only be undertaken at the request of
the JMSP Studbook Keeper. Surplus breeding animals held at JWPT will be moved to
other collections according to the instructions of the JMSP Studbook Keeper and
Species Coordinator. It is important that a healthy captive population, with
broad genetic representation, is maintained as a safety-net until the
distribution and status of this unique frog have been thoroughly assessed and
any necessary conservation measures initiated.
Discussion
Many species, in many institutions, enter collections under the pretext of being
used as pilot, or model, species. This is clearly justified when applied as
described in this paper. Unfortunately, however, the experience gained with the
pilot (or model) is often not moved to the next stage and actually applied to a
rarer taxon. Indeed in many cases it is questionable whether the target species
is ever identified. This is the first time in the Gaherty Reptile and Amphibian
Conservation Centre that a species, D. auratus, has entered the
collection identified from the beginning as a pilot species, and has been used
exclusively and successfully for that purpose. The development of husbandry
skills, experimentation with and refinement of rearing techniques, diet and
lighting regimes, and the subsequent successful management and controlled
breeding of the endangered blue poison-dart frog are the product of this
process.
Furthermore, the experience of working with these two species
has equipped the herpetology staff with valuable skills which can be drawn upon,
modified and developed for the management of other species of Dendrobatid and
similar frogs. In June 1998, for example, two species of dangerously toxic
poison-dart frog, Phyllobates terribilis and P. aurotaenia, were
donated to JWPT by the CITES authorities at Heathrow Airport. Previously
destined for the pet trade, both species of frog, two individuals of each,
settled quickly under the care of the herpetology staff and fortuitously turned
out to be pairs.
Drawing upon previous experience, environmental manipulations
were used to induce courtship and reproduction and both species have now been
bred with great success. Similar brood and tadpole care as used with the Dendrobates
species has proved successful and experimentation with group rearing has proved
beneficial, reducing maintenance requirements and increasing frog size at
metamorphosis. More than seventy frogs of the two Phyllobates species
have been reared and breeding has now been discontinued (by reduction of
vivarium humidity and cessation of rainfall), due to lack of space.
Collection for the pet
trade is one of many threats which face the more beautiful and brightly
coloured species of poison-dart frog. Many are delicate and fare poorly in
captivity, resulting in continual collection pressure to sustain demand, and a
few species are too dangerous to be considered safe. Wild caught P.
terribilis in particular are completely unsuitable for the pet trade due to
their dangerous toxicity (Bertrum, 1994). Less
than 200 micrograms of the batrachotoxin secreted by this species would be fatal
to humans if it were to reach the blood stream through an open wound (Myers et
al., 1978). Fortunately many species are now successfully bred in sizeable
numbers in captivity, though the thirst of the hobbyist for new colour forms and
geographical races means that collection of wild poison-dart frogs is unlikely
to be discontinued completely.
Unfortunately, the
pressure of collectors is a minor threat for most species, in comparison
with the threats many species of Dendrobatid and hundreds of other species of
frogs are facing worldwide (Gibson
and Freeman, 1997). Habitat destruction, global warming, thinning of the
ozone layer and increased ultra-violet radiation, wetland drainage,
agricultural, industrial and domestic pollution, and the recent identification
of abnormal disease are all decimating frog and other amphibian populations
worldwide and exterminating species before we have had even a chance to
understand the cause of their decline and disappearance.
This worldwide decline in
amphibian populations, due to one or a suite of these problems, is one of the
most serious global biodiversity disasters facing the conservation community (Lips,
1997). The instigation of detailed research programmes, habitat protection
and restoration and in-situ or ex-situ captive breeding programmes for
threatened species is crucial to the long-term chances of survival for these,
the most environmentally sensitive of the terrestrial vertebrates. Programmes
such as those for the Mallorcan midwife toad Alytes muletensis (Tonge
and Bloxam, 1991; Buley and
Garcia, 1997) and Puerto Rican crested toad Peltophryne lemur (Miller,
1985) are far from perfect examples, but have combined detailed field work,
captive breeding, reintroduction and monitoring to give these critically
endangered amphibians a fighting chance of long-term persistence.
At present there is very little hope that the main human
pressures that are forced upon natural populations will dramatically diminish,
at least in the foreseeable future. The task facing us at present is huge, but
by evolving programmes such as those here, at least a few of the world’s
amphibian species can be given a fighting chance. At present many governments
are beginning to realise this, and efforts are being made to stem the
destruction of these habitats. By making this long-term commitment the
scientists of tomorrow will hopefully not have to rely on preserved museum
specimens and the documentation and photographic evidence of extinct species to
fuel their knowledge.
Acknowledgements
Thanks to Richard Gibson and Kevin Buley for their suggestions and comments on
the content, and direction. I also thank them for their precise attention to
detail and therefore making many useful corrections. Also thanks to Richard
Gibson for spending valuable time whilst in Madagascar proof-reading the final
drafts. Their long verbal discussions of the paper were also much appreciated.
Many thanks to Anna Feistner and Eluned Price for the final preparation of the
manuscript, and to their patience as the deadline became ever closer.
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TABLE I. Summary of D.
auratus held at JWPT
