The New Zealand native species are threatened by the chytrid fungus Batrachochytrium dendrobatidis, discovered in Archey’s frog in 2001 after their numbers had plummeted. The fungus is thought to have arrived with imported pet frogs. It damages the frogs’ skin, through which they breathe and take in moisture, and may also release toxins.
Five dead Archey’s frogs found in the Whareorino Forest showed signs of attack by rats. Interestingly, the rats left the heads of their victims intact. The frogs have defensive glands around the head and backs that secrete compounds that may be bitter or toxic. Other evidence, largely anecdotal, suggests that native predators as varied as the giant kōkopu (a fish), tuatara (reptile) and weka (bird) may avoid the native Leiopelma frogs.
When tiny Archey’s and Hochstetter’s frogs were picked up by a weka (a flightless bird), the frogs gave off high-pitched squeaks until the weka dropped them. The Archey’s frogs then stood their ground with a head-butting posture, which further discouraged the large bird. Unfortunately, introduced rats and other predators are not so easily put off.
Habitat change affects frogs, and their range has been greatly reduced in the last few centuries. Forest clearance, animals browsing and even routine road work will further deplete native frog populations. Climate change may present other challenges to their survival, despite their 100-million-year survival to date.
In 1921, legislation was passed making it an offence to harm frogs or remove them from their environment. However, to slow their decline, more active measures will be needed – protecting habitat, removing or reducing nearby mammalian predators, and preventing the spread of fungal disease.
Making safer habitats
The highly endangered Stephens Island frog population was restricted to one site on one island. A new habitat was then set up on the island, and 12 adult frogs were transferred there in 1992. They appear to have settled into the new area. In May 2004, another 40 Stephens Island frogs were moved to Nukuwaiata Island in the Marlborough Sounds.
After a trial move to a second site on Maud Island, 300 Maud Island frogs were taken to Motuara Island in May 1997, and in 2006 the population there seemed to be doing well.
The Carter Holt Harvey Native Frog Research Centre at Auckland Zoo is a captive breeding facility for Archey’s frogs, free of the chytrid fungus. The aim is to breed back-up populations in case the chytrid fungus or another ecological catastrophe wipes out the species in the wild. The centre will work with the Department of Conservation to find a cure for the fungal disease that threatens frogs around the world.
Unwanted frog species
It is vital that new species of frog do not become established in New Zealand as they may out-compete native frogs. In 1999, tadpoles of the Australian banjo frog (Limnodynastes dumerilii) were reported from the Waitakeres. The area was thoroughly searched, and several thousand tadpoles, found at a person’s home, were destroyed. Fortunately in this case, the aggressive species does not seem to have become established.