Australian endangered species: Beautiful Nursery Frog

The Beautiful Nursery Frog is found only on Thornton Peak in northeast Queensland. Steve Williams

The Beautiful Nursery Frog (Cophixalus concinnus) is a tiny ground-living frog from the family Microhylidae - from the Greek words “micros”, meaning small, and “hyla”, meaning forest or woods.

The species is only found in tropical north-east Queensland on the top of Thornton Peak in rainforest above elevations of 1100m. It one of the most restricted species of microhylid found in Australia.

A dull brown colour on their back, Beautiful Nursery Frogs are a vivid orange-red on their throat and chest. They are commonly found in the leaf litter on the forest floor, or within crevices in large boulder fields. Males call during or after heavy rainfall.

Unlike typical frogs they breed on land, and their eggs do not hatch into tadpoles. The embryo develops directly in the egg and then hatches out as a tiny froglet. The transparent eggs are laid in a string under rocks or logs in moist soil. One clutch of 17 eggs has been found, under a rock, and guarded by a male in a primitive form of parental care.

Status

Microhylids have made north Queensland their home for a very long time; scientists have dated the origin of these frogs to many millions of years ago. They persisted during the rapid rainforest contractions of the late Pleistocene, most likely because they were small enough to survive in populations in rainforest pockets.

Male Beautiful Nursery Frogs have been found caring for their eggs. Steve Williams

But this means that some, including the Beautiful Nursery Frog, are hanging on in very small rainforest areas – the total distribution of the species is little more than seven square kilometres. However, they are abundant within their range, although due to their cryptic nature there is currently no reliable estimate of population size.

Threats

The primary reason for the critically endangered status of this species is its restricted geographic range – the total area of suitable habitat is estimated to be only 718 ha, and all individuals are in one single location.

This species is also highly vulnerable to climate change. Possibly the most important impact of climate change on this species, which relies upon a consistently wet environment, will be the predicted decrease in cloud cover.

Climatic models predict that an increase in temperature of only 1 or 2 °C will lift the cloud base to higher altitudes, meaning that the cloud-stripping potential (the capture of water droplets on vegetation) will decline significantly and water loss through evaporation will increase.

For this species, restricted to a single mountain top, and for whom cloud cover is of vital importance, there will be nowhere left to go in order to stay cool and wet. Climatic and ecological models predict the species may be extinct within 50 years.

Unlike many other frogs in the Wet Tropics region, microhylid species fortunately do not seem to be affected by the deadly chytrid fungus. This may be due to their terrestrial lifestyle.

Strategy

There is currently no recovery plan in place for the Beautiful Nursery Frog. Details of its population status and aspects of its biology and ecology remain a mystery due to its location and cryptic nature. Because they do not call, females are very rarely encountered.

However, monitoring trips have been made at regular intervals over recent years, and efforts are underway to find out more about this species. Researchers at James Cook University have identified that the frog has one of the most general diets of all Australian microhylids, which could help it persist in such a restricted location.

The boulder fields on Thornton Peak are also key to the persistence of the species; studies show that the temperature within the boulders can be as much as 10°C cooler than in the open, protecting the frogs and keeping them cool and wet.

Conclusion

Lack of knowledge about the population size and trends and information on its physiology and ecology impede efforts to provide a recovery plan or management strategies.

Some aspects of the ecology of the Beautiful Nursery Frog could help it persist and adapt under predicted climate change, including its generalised diet, and tendency to shelter within deep crevices in large boulder fields.

Mitigating climate change through a reduction in greenhouse gas emissions is the best hope to save this species. Assisted migration is not likely to be an option given the frog’s restricted, high-altitude range. And while the provision of man-made shelters or refuges could be utilised for other microhylid species, protection of the Thornton Peak boulder fields will be of greater help to the Beautiful Nursery Frog.

The Conversation is running a series on Australian endangered species. See it here