Native Frogs

Samantha Russell
Field Biology
New Zealand Conservation Issues
April, 2009


New Zealand’s Frogs are Croakin’!
(which is ironic, because native frogs don’t actually vocalize)

“When pesticides, agrochemicals and heavy metals find their way into ponds, streams and lakes, bad things happen to frogs,” said one article in New Zealand Geographic. New Zealand is no exception to this claim, and adds that bad things happen to frogs when new predators and new parasitic fungi are introduced, as well as when habitats are lost.
Native New Zealand frogs, like the much of New Zealand's fauna, are a bit different from their amphibious counterparts throughout the rest of the world. New Zealand's frogs don't have a tadpole stage--that is to say that they hatch as fully formed little froglettes--and are incubated and cared for, briefly, by their father. New Zealand frogs also don't have webbed feet--convenient as they don't require standing water or really much water at all to reproduce--nor do they croak which is convenient as they lack an external eardrum as well. These are all things that link New Zealand's frogs more closely to Jurassic era frogs; another remnant of New Zealand's Gondwanaland connection. Fossil records indicate that they have changed little over the past 150 million years.
Prior to any human colonizing New Zealand, fossil records show that there were seven species of frog; spread throughout the North and South Islands. However, presently, there are only four species of native frog, three of which are at a critical risk of extinction. As alluded to above, New Zealand native frogs are threatened by non-native fauna, pollution, habitat loss, and an introduced fungus; Batrachochytrium dendrobatidis (Chytrid).
There are two main sources of competition from animals introduced to New Zealand; the Kiori (Rattus exulans Peale) and the Eastern Banjo Frog.
New Zealand frogs evolved in conditions without any mammalian predators. That is to say, the frogs developed in an environment where their main predators were birds that hunted by sight. Therefore as a primary defense, New Zealand frogs simply freeze when threatened. The introduction of rats, and later other mammalian predators like weasels, stoats, and ferrets, sharply reduced frog populations. The frogs hadn’t developed evasive techniques or even defensive poisons to defend against these new predators and the consequences were tragic.
However, currently there is some research being done to determine whether or not mice pose a threat to New Zealand’s frogs. Maud Island Frogs were found to have successfully bred on the North Island and a comparative study of population survival is being carried out. If mice are found to not be a threat, a wide variety of new land will become available for potential frog introduction projects.
The Eastern Banjo frog introduced from Eastern Australia also poses a threat to New Zealand’s native frogs. The Eastern Banjo frog competes with native frogs for food and habitat, and has even been known to eat the smaller, native frogs.
Pollution is another huge threat to New Zealand’s native frogs. Because of the duality of an amphibian’s life (being that they thrive on both land and water) and because amphibians absorb much of the world around them through their skin, they are especially vulnerable to toxins. Runoff from agricultural centers, roadways, home yards, parking lots, etc carries poisons to the frogs where they are internalized and deformities occur. These deformities not only weaken the already dwindling gene pool of the frogs, but also reduce the number of frogs able to contribute to that gene pool. Runoff isn’t the only source of toxins that affect the frogs—all forms and types of pollution occurring in New Zealand, and globally, trickle down to affect frogs.
Habitat Loss is another issue that affects New Zealand’s native frogs. The frogs once were found throughout the damp forests of New Zealand. However, as Maori and Pakeha alike have altered the landscape in geologically recent times through burning, building, and conversion to sheep friendly land, the forests have dwindled as have the frogs.
The issues of global climate change are also affecting frog habitats, according to a New Zealand Geographic article. Much of New Zealand’s forests occur in and around alpine zones. As the world warms, alpine regions also warm, and are moved to higher elevations and are thusly reduced in size. This limits native frogs’ habitable regions.

Sign at Orana Park by S. Russell

According to Bruce Waldman and Julian Motha, Batrachochytrium dendrobatidis or Chytrid is a fungus that infects keratinized (for example, the epidermis) tissues of the host. Most types of Chytrid are not known to infect vertebrates, so it is unusual and a bit alarming that it has been found in frogs. Waldman and Motha say that, “Many consider Chytridiomycosis a new emerging infectious disease that may be driving global amphibian decline and species extinctions.” They also mention in their article that something may be affecting amphibians globally that is reducing their ability to fight off previously manageable pathogens.
Chytrid is thought to have entered New Zealand through the pet trade—non-native tadpoles carrying the fungus may have been released and transmitted the fungus to the native population Other possible transmitters of the disease include on the boots, field gear, fishing equipment, boats, etc. Waterfowl have also been cited as potential transmitters.
Further investigations into the transmission, causes, and effects of Chytrid are currently being done throughout New Zealand, with quite a bit going on at University of Canterbury.
Presently, the exact numbers of all four species of frog are unknown—it’s awfully hard to do a frog census, when no one is croaking. However, two species (Archey’s frog and Hamilton’s frog) are listed as New Zealand Nationally Critical, the Maud Island frog is Nationally Endangered, and Hochsetter’s frog is listed as at risk. Archey’s frog is listed as a number one conservation priority by the international Evolutionary Distinct and Globally Endangered program due to its genetic distinctiveness. New Zealand’s Department of Conservation suggests that individuals can help preserve frogs by reporting any sightings of native frogs, photographing them if at all possible, and recording the type of habitat, time, and date that the frog was sighted in. The DOC also implores individuals to avoid touching the frogs. These actions taken to help generate more information about the frogs, along with efforts to curtail pollution, carbon output, habitat encroachment and the spread of non-native predators can help to preserve and protect these highly unique remnants of Gondwanaland.


















Works Cited

“DOC’s Work with Frogs.” http://www.dog.govt.nz/conservation/native-animals/reptiles-and-frogs/frogs/. 4 April 2009.

Hansford, Dave. The New Zealand Listener. “A Great Leap Forward?” November 2006.

Hansford, Dave. New Zealand Geographic. “Two degrees from Oblivion.” Sep/Oct 2008.

“Tiny NZ frog leaps into conservation history.” http://www.newzealand.com/travel/media/press-releases/2008/2/08_feb_29_nzfrogshatch_pressrelease.cfm. 29 Feb 2008.

Waldman, Bruce, and Julian Motha. Surveillance. “Chytridiomycosis in New Zealand Frogs.” 28(3) 2001.