New Guinea has the most diverse array of tropical island frogs in the world and its mountains and forests are still revealing their secrets.
This month, no less than five new species of frog have been described by scientists from the Queensland and South Australian Museums and Griffith University, who published their results in Zootaxa.
Among the new species is one with a bird-poo-like appearance (above) when young that changes as it matures, and another named for its blood-red belly.
The study's lead author Steven Richards, an honorary researcher with the South Australian Museum, spent the last 30 years collecting the new specimens from Gulf Province and the New Guinea Highlands.
"[Papua New Guinea] is spectacularly beautiful and it's very rugged, so it can be difficult to get into a lot of those sites — it definitely has its challenges," Dr Richards said.
"But when you [have] those spectacular finds, it makes it all worthwhile."
Study co-author Paul Oliver from the Queensland Museum said there are between 530 and 540 known frog species in PNG, but many more that still haven't been scientifically classified.
"We're definitely estimating there are well over 700 frogs, which is basically more than any other tropical island area in the world," Dr Oliver said.
"It leaves Borneo for dead and it's way more than Australia. Australia has got about 250. So it's an insanely diverse frog fauna."
But pictures tell a thousand words. Here in no particular order are our five newly classified amphibian friends.
Red-bellied tree frog (Litoria haematogaster)
The red-bellied tree frog is only known from a single location on the Darai Plateau in New Guinea's Gulf Province, in the country's south.
Haematogaster literally translates from the Greek "haema" meaning blood and "gaster" for belly, in reference to the bright red abdomen of the species.
"It looks pretty enough [from above], but when you turn it upside down it's got that brilliant red underneath," Dr Richards said.
"It's presumably some kind of flash marking to startle predators when they jump or if they get flipped over."
Lisa's tree frog (Litoria lisae)
Lisa's tree frog is named for Dr Richards's wife.
It was found in the lower forests of the Gobe and Iagifu Ridges in the Kikori River basin in southern PNG, and was only found in limestone karst habitat.
"It's an unusual frog because generally speaking there's not a lot of water at all in the [karst country] and they seem to be calling from down in things like sinkholes," Dr Richards said.
"It's difficult terrain and it makes them difficult to collect because it's quite dangerous to go down into sinkholes trying to catch them."
Darai Plateau tree frog (Litoria daraiensis)
Like the red-bellied tree frog, the Darai Plateau tree frog is only known in one location, from where it gets its name.
And like the other four new species, it's in the Litoria genus, Dr Oliver said.
"They're climbing frogs. So the vast majority we call Litoria have got expanded toe pads and finger pads."
The Darai Plateau tree frog's hands and feet are also translucent.
Slender spotted tree frog (Litoria gracilis)
The slender spotted tree frog was found in several locations in the foothills of the PNG Highlands.
As well as describing the new species, the researchers also analysed its unusual method of reproduction.
Instead of laying its eggs directly into a water body, the slender spotted tree frog glues them to leaves, presumably for protection from predators, Dr Richards said.
"They turn into little tadpoles and then they drop [into the water below].
"They can do that because it's such a wet place. I've worked in places in New Guinea where they get nine metres of rain a year."
Crater Mountain treehole frog (Litoria naispela)
The Crater Mountain treehole frog's scientific name — naispela — is Tok Pisin (a PNG creole language) for "attractive" or "beautiful".
But the researchers suspect its colouring early on in life is meant to give predators a different impression.
Like the slender spotted tree frog, Litoria naispela doesn't lay its eggs directly into water. Instead, it glues its eggs to the trunks of trees above tree hollows.
When the tadpoles are ready, they're washed down the trunk into the water-filled tree hollow to mature.
But when they first emerge from the hollow, they don't have the green and white "naispela" markings of their mature form.
Instead, the researchers think they've evolved a bird-poo mimicry to avoid being eaten.
"The locals said ... all those tree hollows where I found those frogs coming out are well known as bird drinking spots," Dr Richards said.
"It's interesting that the little frog coming out looks like bird poo.
"What a great strategy to avoid predators — it's a hypothesis but I reckon it's a pretty good one."
Dr Oliver said bird poo mimicry isn't as rare as we might imagine.
"There are frogs in South America and frogs in Asia that do the same thing. And there are also lots of insects that do the same thing.
"Our local baby orchard swallowtail [butterflies], their babies are dead ringers for poo.
"But what's cool is again it emphasises that the New Guinea frog fauna is really diverse, and we're only ... just scratching the tip of the iceberg in terms of the cool things that New Guinea's frogs do."
