Whistling frogs in Rotterdam Zoofrom: Blijdorp Blad, Spring 2010
Since 2001 there are Montserrat whistling frogs housed in the Oceanium. The whistling frog with a length up to 23 centimetres is one of the biggest frog species we know. Within the family of whistling frogs this species has the biggest larvae that can even reach a length of 11 centimeters.
Originally this species could be found on six island in the eastern part of the Caribbean. However, in the last decades they are only living on Montserrat and Dominica.
From early days these animals with their meaty legs tasting like checken were the national dish of the islands. That is why they are referred to as “mountain chicken” or “pollitos de las montañas”.
On Montserrat catching these animal from the wild has almost stopped, but on Dominica the hunters are still active, catching vast numbers of frogs. Every year between 8000 and 36.000 animals are caught.
Population growth, cultivation of the frog’s habitat and introduction of rats, mice and pigs have paid their debt. After the vulcano eruption on Montserrat in 1995 the lava flow killed many animals. The rather small habitat declined even further by burning, acid rain and ash fall. To make matters worse in 2002 a deadly amphibian disease called chytrid fungus has arrived on the island, which has also been found elsewhere in the world causing the death of hundreds of amphibians.
From the thousends of frogs that used to live on Monserrat no more than a few hundred have survived and are living in an area of some 17 square kilometres.
Already before the arrival of the fungus on Montserrat the Durrell Wildlife Conservation Trust (DWCT) had started a rescue operation by catching a long dozen of frogs and sending them to the Channel Island of Jersey. After a year the first descendants of the captive frogs were born. Those frogs were sent to various zoos, four of them arrived in Rotterdam Zoo in 2001. Because Rotterdam did not intend to start breeding at that time, 4 males were sent. First of all we had to gain experience how to house and feed them. At a later date we might participate in the European Studbook (ESB) that “Jersey” had started.
Keeping whistling frogs was not that easy, in 2005 and 2008 three animals died unfortunately. The grown frogs appeared to need more space per frog then we had thought. In 2008 we received animals again, one male and three almost fully grown females. The male from 2001 joined the new group.
After fertilizing the frothy nest will harden so that it can bear the female’s weight. The nest is guarded by both male and female. The female will often stay in the nest cavity. After hatching the female feeds the froglets during 7 weeks by laying unfertilized feeding eggs every one to seven days. During the entire feeding period that will be 10.000 to 25.000 eggs! In a clutch the froglets are hanging from the abdomen of the female. After a larval stage of 6 to 8 weeks the metamorphoses from larvae to little frog follows which will take 2 to 7days. The entire process takes place on land and not in the water which is the case with most other amphibians!
So far breeding has not been successful in Rotterdam Zoo. Between May and December 2009 one of the females built two frothy nests, unfortunately no eggs were found. May be the females were not yet sexually mature.
This May we started to imitate the rainy season in the frog’s enclosure.We also installed an infrared camera in the nest cavity to follow the process. In this way the keepers are able to observe what is going on and zoo visitors can follow the process via internet.
… so far breeding has not been successful in Rotterdam Zoo …
Also on Montserrat a breeding centre has been built recently. During continuous field work the number of animals is closely observed so that shrinkage can be noticed at an early stage. Regularly work shops are organised for local rangers during which the chytrid fungus problem is highest on the agenda with an important role for the Durrell Wildlife Foundation.
In 2009 DNA research has proven that de animals from Montserrat and Dominia belong to the same species. Therefore it is possible to bring the offspring from animals that have been exported from Dominica to Europe to Montserrat. We do hope that Rotterdam Zoo will be able to contribute to the reentry of this critically threatened species to its original habitat.