Collecting corroboree frogs

Written by Gerry Marantelli and Joanne Doherty of the Amphibian Research Centre in Melbourne and published in mid 1997 in "In the Spotlight" (Vol 3, No. 2).

Part 1 of the corroboree frog husbandry project

The Corroboree Frog (Pseudophryne corroboree) is without a doubt one of the most spectacular of Australia's amphibians. Its dazzling bright yellow and jet black markings make it one of our most readily recognisable frogs. Its uniquely Australian name coupled with its highly photogenic nature have led to it being one of Australia's best known frogs both here and abroad. With less than 300 of these brilliantly coloured frogs left in the wild we stand in real danger of losing this Australian frog icon.

Over summer Corroboree Frogs occupy the damp vegetation surrounding bogs and seepages in the Snowy Mountains of New South Wales. Although once abundant in the snow fields, this species is now in serious danger of extinction as population numbers have fallen significantly. The cause of the Corroboree Frog decline is presently unknown. Pollution tests have suggested that contaminated water supply is not a contributing factor, while there is speculation that increasing ultra-violet radiation due to ozone depletion may be responsible.

In response to this alarming situation a joint effort between the University of Canberra, the Australian Nature Conservation Agency (ANCA), the New South Wales National Parks and Wildlife Service (NSW NPWS) and the Amphibian Research Centre (ARC) has lead to the initiation of a recruitment enhancement project. As the agent causing the decline in Corroboree Frogs is unknown the project's aim is to artificially elevate the population numbers until the cause of the decline can be determined and resolved.

During the last winter period the temperature dropped below zero in a number of the ponds at Corroboree Frog sites. Although this may be a natural occurrence it is likely that it also contributed to the very low over-winter survival of eggs and tadpoles recorded last year. In an effort to reduce mortality during this stage eggs have been removed and are being raised at the Amphibian Research Centre under temperature controlled conditions. By removing eggs from the wild and rearing them in captivity through to the late tadpole stage before releasing them to the wild; it is hoped that survival will be increased. The specific bogs from which each clutch of eggs were removed has been recorded so that the tadpoles can be returned to their original nest site. Decomposing material from each site has also been collected to ensure the tadpoles have access to their natural food. Releasing the tadpoles to their original nest site may be important as scientists have evidence that some frogs return to mate in the ponds in which they developed.

The field work launching this conservation effort occurred during the mating season of 1996-97. At this time male nest sites at Mt. Kosciusko were marked individually by David Hunter from the University of Canberra. Males were located by listening to their call and triangulating the precise position of each nest. Males that were not calling enthusiastically were enticed to respond to a loud shout to pinpoint their location. Use of these methods should have ensured that almost all the potential nest sites were marked prior to the egg collection to allow egg masses to be found with minimal disturbance to the habitat.

Our departure from Melbourne in the early hours of Saturday March 15th was punctuated by a rather long encounter with the staff from Avis, from whom we had booked a hire car several days earlier. On arrival at Melbourne Airport we were informed that they did not accept cash and as we had no credit facilities we could not take possession of the car! Over an hour of negotiating and several hundred dollars later (cash deposit) we managed to obtain the required vehicle. Not a hopeful start to such an auspicious event. About 3am on the Hume highway somewhere near Shepparton a large ball of white light descended from the sky, fell behind some trees and appeared to explode (a dull orange glow rose above the trees immediately after the object disappeared from view). A little further along the highway what appeared to be glowing embers on a hillside were visible in what by our reckoning was the site of the above mentioned event. We abandoned our efforts to get closer to the site after about half an hour of following small tracks and not getting any closer. We were not sure if this was a good omen, but it provided the conversation that kept us awake for the rest of the trip.

We met up with Will Osborne and Dave Hunter (University of Canberra) and Ken Green and Craig Smith (NSW NPWS) at 10am and then loaded into 4WDs to travel to the collection sites. The next two days were spent searching through the moss at each of the previously marked nest sites. At each site where eggs were located, all the eggs were removed and counted. Each egg was recorded as either live, dead, or empty (possibly hatched). Half of the live eggs were returned to each nest site and half were packed in moss to return with us to Melbourne. Only five adult Corroboree Frogs were observed, all of which were males and each was situated above his egg clutch. Once caught, one toe was removed from each frog and placed in a preserving solution for future analysis - similar to that of ageing a tree by counting the trunk growth rings, a frog can be aged by counting the bone developmental rings. At the same time a photograph was taken of each frog's characteristic throat patterns. In the future when the frogs are found again their development and location can be recorded allowing the history of each individual frog's life and movements to be recorded.

By the end of Sunday a total of 378 P. corroboree eggs had been collected for return to Melbourne. We also had on board 13 adult P. pengilleyi along with about 100 P. pengilleyi eggs. Our van was loaded with moss and detritus from every nest site, and although worn we were all satisfied that the exercise had come off according to plan. On our return the process of unpacking and setting the eggs up for raising occupied us for two full days.

Of all the individuals transported we recorded no losses, only a few eggs were slightly damaged, but even they have now successfully hatched. Two weeks after the return to Melbourne we have had only a few eggs lost and two successful spawnings from the P. pengilleyi. It already appears from a recent conversation with Dave Hunter that the captive eggs are fairing a little better than their wild siblings. Enclosures have now been erected around each nest site in the field so that predators can be excluded and survival for comparison with the captive animals can be accurately recorded.

This project is the most substantial of its kind ever undertaken in Australia. If it is to be successful the captive animals must achieve better survival than those in the field, as well as be successful (compared with their field raised siblings) after they are released. Long term monitoring of both the released and field raised animals will give us a clear picture of how well we have been able to elevate the populations with the use of captive technology. The extent to which we continue this project will be determined based on this years success. Future efforts may involve the removal of a much larger proportion of eggs from more sites if this technique proves valuable.

The extent to which further efforts can continue will also be influenced by funding. Only $11,000 has so far been allocated to this project, which has been barely enough to cover minimal equipment costs. Ongoing expenses will have to be met by funds raised by other means. As the cause of the decline in Corroboree Frogs still eludes us, this attempt may be their last hope for a recovery. If it proves unsuccessful the species will probably not last the next five to ten years.