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.
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.