Black Treefrog

A couple of days ago my system informed me that, “A new comment on the post Green Tree Frogs – not always green is waiting for your approval.” Readers come up with some fascinating observations so I clicked through straight away. Here’s the email conversation which followed, complete except for the usual greetings, etc.

Yvette: Hi Malcolm,

I live in Darwin NT and have many green tree frogs in the garden. I hunt and catch cane toads every night and came across a black tree frog. I’ve seen many dark green but never black. Have you heard of black tree frogs before? I have a photo of it next to a green one which I’m happy to email to you if you wish.

Malcolm: Black? New to me! I would love to see a photo.

I’m no frog expert but I looked around on frogs.org.au and found one black frog that’s supposed to live in Darwin, Limnodynastes lignariusIt’s not a treefrog, though.

Yvette: Yeah new to me too. We have dozens of green tree frogs of various shades in our garden but this is the first black one we’ve seen. I had to get my hubby Mark to confirm that, yes it really was black!

I googled black frogs also which is how I found your site. Have attached a couple of pics. Let me know what you think.

Malcolm: Thanks for the photos [cropped for publication].

I think you’re right – a very, very dark Green Tree Frog seems to be the only possibility. I played with the photos in my image editor, over-exposing them, and it is clear that the underlying colour is greenish rather than brownish. The red eyes, I guess, are just the red-eye effect of the flash.

I would like to post all this on my blog, if that’s okay.

Yvette: Yeah, go for it.  … I went out again later to see if he was still around and found him playing leap frog (minus the leap) with the green one. While still very very dark, he had a slightly greener tinge. Maybe it was a mood thing. :-)

Yvette (later): Apparently black tree frogs are quite common here according to NT Parks and Wildlife, however no one is clear on why they appear so black. My son found two in his yard this week and was also surprised at how black they seemed. We’ve been here for 20 years and this are the first we’ve seen. We’ve seen many dark olive green frogs though.

Thought I’d pass this on and will continue to update you with further info if we receive any (if you wish).

Malcolm: Yes, please do – and thanks again for your photos and for getting in touch in the first place.

A bit more searching on the net found me this page which says,

While extreme changes in color, for example a frog who is always mostly green turning and staying a dark brown, can indicate stress or illness, changing shades of colors is a normal and natural process for these frogs. Part of these variations in color are an indicator of mood changes, and part of them are a means of camouflage.

This page [Kroten.com, link dead as of Aug 2020 -Ed.] adds more support to the theory:

Several tree frogs have a super ability to melt from one color to the next.  Frogs have three layers of pigments that they can change. Color morphing can be subtle or dramatic. The changes are not based on environmental color as much as they are on the temperature and light background. A frog is likely to change color during the seasons. Many times the change takes weeks to complete, but a noticeable difference in color can be observed within hours. The frog slowly blends into the lighter or darker trees of summer or fall. Not only does this provide some camouflage for the frog, but is an energy and heat conservation tactic. When the weather is warmer, the frog will be lighter so as to reflect heat and stay cooler and vice versa with cooler temperatures. The frog will become darker to soak up heat and create more energy. Whites Tree Frog changes from green to brown.

Neither of these are high-powered science sites so treat their information with due caution although it does match your observations. Yours is by far the darkest I’ve seen, whatever its reasons for going black.

Green Tree Frog

close-up of large frog
Green Tree Frog

I don’t know how many frogs we have in our garden but we have seen this one a few times in the last week. He (she?) is a Green Tree Frog, Litoria caerulea, and is a very large member of the species. Wikipedia reckons they reach 10cm and he was at least that big – he is resting on large adult male hands here. I will measure him next time I see him.*

Yesterday I discovered him enjoying the cool water in the bottom of our old concrete laundry tub and hauled him out to take a photo on the way to a safer place. As I noted a while ago, they adapt their colour to their surroundings and this one had spent hours trying to look grey-brown. He didn’t manage to change as much as this virtuoso, however.

Handling frogs is not generally recommended because salt, oils and traces of other chemicals on our skin can be passed on to them and harm their health. Their damp, delicate skin is easily damaged by rough handling, too. Washing our hands in clean water and handling the frog immediately after – with our hands still wet, as seen below – is best for them.

Frog on hands
Another view of the same frog

* We measured him the same evening: 11.5 cm. Wikipedia is wrong!!

Frog fortress

We have quite a number of Green Tree Frogs, Litoria caerulea, in our garden but they don’t live where their name would suggest they live. The species has adapted very happily to suburban life and they sit every evening on windowsills outside lighted rooms, feasting on insects attracted to the lights; or they come indoors like this one; or they catch some warmth on the edge of the birdbath; and so on. Around this time of year they get pathetically optimistic about breeding opportunities (never mind that it hasn’t rained for months!) and call out in response to lawnmowers, dogs barking next door, motorbikes, aeroplanes and anything else that makes a baritone grawwrk!, so we know there’s one in the laundry tub drain pipe, too.

cement bricks with a glimpse of frog noseBut they can still surprise us.

A couple of days ago we spotted a shiny dark – something – in the cement-brick base of a garden seat. It turned out to be the nose of a frog, and he had a neighbour in the adjoining brick. The holes were barely wide enough for me to fit my thumb through and the frogs were well grown – even their noses looked too big to fit through the holes, let alone their bodies. There were no other ways in or out so we decided they must have got in there when younger and survived ever since on passing ants.

To the rescue!

lifting the top brick out of the way

the two frogs in their cells

close-up of one of the frogs

Green Tree Frogs? They certainly weren’t green, but we weren’t surprised since we know they change colour to match their surroundings. The darkest I have seen were in Reef HQ Aquarium; I showed one here with a more normal one for comparison.

They were also not keen to escape. In fact, we needed a hose and quite some time to persuade them to hop out. Then we patted ourselves on the back for our kindness towards dumb animals, put the seat back together and went on with the rest of our lives.

Next day we were out there again but when we looked at the bricks we had to laugh at ourselves and marvel at frogs’ ability to squeeze through tiny gaps: two dark shiny noses poked up out of their holes. So much for our rescue!

The Rainforest comes to the Aquarium

Reef HQ Aquarium has carried out some major projects recently. Some of them are still under way but I am happy to report the completion of the Rainforest Tree exhibit:

Rainforest tree exhibit
The Rainforest Tree exhibit, modelled after the trunk of a fig tree

One might ask why an aquarium celebrating the Great Barrier Reef should need a rainforest exhibit but the answer is fairly simple: the rainforest is all part of the same ecosystem, intimately linked through the water cycle. Rains fall on the hills, and the water drains through the rainforest, farmlands and mangroves to the coastal waters of the GBR lagoon. What happens to it on the way –  picking up sediments and nutrients, for instance – has immediate effects on the seagrass and corals, and on everything that lives on and amongst them. The aquarium has a lovely freshwater wetlands exhibit next to the tree with a mangrove exhibit not too far away to complete the sequence.

The three glass-fronted display cases contain (left to right) Green Tree Frogs, a Green Python and Red-eyed Tree Frogs. I have already posted a picture of the first of these – here – so here are the other two:

Red-eyed tree frog on branch
Red Eyed Tree Frog, Litoria chloris

Something funny about its eye? Read about the nictitating membrane.

Green Python
Green Python, Morelia viridis

The Green Tree Python is a beautiful creature and has pride of place in the exhibit. She isn’t as thrilled by that as the aquarium’s visitors are by her, being nocturnal by nature. However, she does often sleep where people can see her.

Green Tree Frogs – not always green

Reef HQ Aquarium has been building a rainforest display for the last few months and it has reached the stage at which animals are introduced. This one surprised me:

a very dark Green Tree Frog
Green – yes, really – Tree Frog, Litoria caerulea

The Green Tree Frog, Litoria caerulea, is very common around Townsville – indeed, all the wetter parts of Queensland – and it usually merits its common name. Here, for instance, is one in my garden:

Green Tree Frog
Green Tree Frog showing more normal colour

The Wikipedia article does say, ‘Its color depends on the temperature and colour of the environment, ranging from brown to green,’ and we often see examples with a dull olive-green coloration but the one in Reef HQ in a (so far) black and grey-brown setting is the most extreme I have seen.

More information: frogs.org.au. The home page will take you to all sorts of useful or fun stuff about frogs.