Sabah, Borneo: Tree Hole Frog

I left one frog out of the reptiles & amphibians post because, after I identified it, I think it deserved its own, admittedly quite short, post. So here it is!

The frog in question was the Bornean Tree-hole Frog, endemic to the island. We came across this miniature wonder whilst walking through rainforest near Sepilok after dark. There was an strangely loud sound coming from near the path, but when we searched the trees, we couldn't see anything. It wasn't until our guide pointed out a tiny frog inside a small, water-filled hole in a thin tree that we had our answer. At first, it didn't seem possible. It was only when we saw the vocal sac moving that we realised that the tiny frog in the hole really was the critter behind the sound. I got out my camera and filmed the frog calling for a bit. Here's what I got:

I found it incredible that such a small frog can create such a loud noise. But there is a scientific explanation behind it, and its very clever. It turns out that these frogs use the holes for their own benefit. Here is an extract of the explanation given by scientists Lardner and bin Lakim: "the male Bornean tree-hole frogs actively exploit the acoustic properties of cavities in tree trunks that are partially filled with water and which are primarily used as egg-deposition sites. By turning their vocalisations to the resonant frequency of the hole, which varies with the amount of water that it contains, these frogs enhance their chances of attracting females". Effectively, these frogs use the water-filled holes to make their calls louder so they can be heard from further away and attract a mate from further away. Lardner and bin Lakim also found that the frogs change the frequency of their calls to adjust to the amount of water in the hole, to get the best sound possible. Lardner also said: "...presumably - we can only guess - the female also appreciates a powerful, strong call as a trait that indicates a powerful male"

In fact, if you look at the video above, around half way through, you can see the male frog moves and fidgets a little, which must be it trying to achieve the perfect sound. When the frog moves to the left, the sound changes. It seems that holes in trees play a very important role in the frogs' life. A good hole means a good performance, which in turn could mean a good mate.

After reading up on these frogs it has become apparent how unique and interesting they actually are. Researching things that you see outdoors is a great thing to do, as it not only expands your knowledge, but also gives you a greater understanding of why things happen and how the natural world works.

If you would like to read more on this here are some links:
AskNature article
National Geographic article
Ecology Asia Fact File

Thank you for reading and I hope you enjoyed this more factual blog post.


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