Identifying tadpole food in floodplain wetlands

A while ago, I wrote about looking for the end of the food-chain. My co-workers and I had dissected some common species of tadpoles from floodplain wetlands and inspected their gut contents under a microscope. We had found they eat a wide variety of things, from tiny crustaceans and other small insects to bits of aquatic plants and long strands of filamentous algae.

The long, long gut of a marsh frog tadpole.

But I wanted to know, what was the most important thing that they were eating? I’d had a feeling the answer was going to be “even smaller things”, and it turns out I was right!

To answer this part of the question, we did a chemical analysis that compared samples of tadpole muscle tissue with samples of food items such as wetland plants, tree leaves, algae, those teeny tiny crustaceans living in the water, and biofilm. It is a method called stable isotope analysis and it works along the lines that ‘you are what you eat’. And as we report in our new research paper, these results suggested that biofilm was most important. (Twitter summary here). (Full disclaimer, we’re mostly confident that it was biofilm… in some wetlands at some times for a couple of species of tadpoles. Check the paper for all the details, PM me for a copy).

And what is biofilm?! Biofilm is basically a super nutritious mix of very small things like bacteria, microbes, fungal hyphae, and teeny-tiny invertebrates, that looks like a filmy, fuzzy goo growing on the surface of leaves and branches and anything underwater.

biofilm – the filmy, fuzzy goop growing on surfaces under water.

Our results were interesting, because when we compared what was in the muscles with what we had seen in the gut contents, it looked like tadpole diet is more a case of ‘you are some of what you eat and not necessarily the most obvious or biggest thing’.

The small end of the food web, biofilm supports marsh frog tadpole growth in some Murrumbidgee floodplain wetlands (NSW, Australia)

So, while pieces of plants or long strands of algae were often jam-packed in the tadpoles’ guts taking up a lot of space, they were not contributing much nutritionally. It looks like the really small and least obvious thing growing underwater is a high quality, nutritious snack supporting the growth and health of bigger lifeforms!

Lots of algae, not so much nutrition!

There is definitely more to know before making strategies for wetland management that will support lots of good tasty biofilm and in turn support tadpole growth, but we’re starting to build evidence for what we only suspected before. For example, see Altig et al 2007, Schiesari et al 2009, Schmidt et al 2017. And I definitely suggest doing both gut content dissection and stable isotope analysis, if you want to find the important end of the tadpole food-web.

A glorious Lower Murrumbidgee wetland… good tadpole habitat.

That time I went to Komodo Island…

I visited the Komodo National Park last year (April 2018), cruising the islands on a six-day boat trip with some very good friends. Our main purpose was to find as many skinks, geckos, snakes, lizards, and frogs that these islands could offer up (all things herpetological). Plus, all the birds, bugs, slugs and ocean-dwelling creatures that we might see while doing so. It was, simply, the best.

So many things could be said about Komodo NP and the infamous Komodo dragons, or the other animals that we saw, the snorkelling we did, even the food we ate, that since returning from that holiday I didn’t know where to start, so I just avoided saying or writing anything. Plus, I didn’t think any of my photos were that great. But I’ve just had a reminisce through the pictures I took and many of them made me smile with the memory or the story behind it. So, I decided that is what I want to share…here are three of my favourite photos from my trip to Komodo NP not because they are the best photos, but because they have the best moments attached to them.

Gates on the toilet block to prevent dragon access.

This photo is from when I realised that the visitor toilet facilities on Komodo Island have something similar to a child-barrier-gate to stop the dragons getting in. Like this but less fancy. It’s those low dark brown doors on the concrete building, see the inset. Because you wouldn’t want to go in and find a dragon backed into a corner annoyed that you’re blocking the exit. And you also don’t want to be in there enjoying the facilities and have one come in after you, because then you are staying in there until the dragon decide it’s time to leave, and that could be the next day! And as our guide explained, that has happened…!

A very elegant solution to a problem I hadn’t thought existed, using child-sized barrier doors to stop dragons disturbing tourists on the toilet, marvellous.

They are big and loud and angry, but adorable and colourful.

This is from our third night, and I remembered it being very relaxed as we spread out to search through the open grassy woodland in the dark, coming together when someone’s excited voice indicated they had found something.

I have good frog-spotting eyes, but it turns out they are less good at finding skinks and lizards at night compared to my pro-friends. So I was particularly thrilled when I found this cutey before anyone else did. It’s a tokay gecko (Gecko gecko), and a small one at that, about 15 cm nose to tip, so probably a recent hatchling or juvenile. It wasn’t the first tokay we’d seen on our trip or the first that night. But it was the first I’d seen first, and I had spotted a baby one, and baby anything is just much cuter and more special. So I snapped a few photos first (this was the best one!), before calling the others over. Tokays are the boss. They have spectacular blue and orange colours, a very distinctive call that echoes through the forest or around your cabin, and they grow to be one of the largest geckos in the world getting up to over 30 cm long. Boss.

Tokay reading: trade in wild tokay geckos

Komodo dragon quits modelling

It’s actually quite easy to get a photo with you and a komodo dragon. Which seems ridiculous, as they are a mildly venomous, extra-large dragon that can actually run quite fast. However, the ones in the most visited area of the National Park seem quite used to people being around, so nearly everyone who goes to the island ends up with a group photo that includes a komodo dragon. It’s just about finding one looking very ‘dragon-y’ (generally lying down), then standing a few metres behind it, while your guide snaps off your iconic Komodo Island new profile photo. While I have a couple of those, I like this one the best. After getting the classic shot, the dragon decided it wasn’t keen for more modelling and started to lumber away, but we kept moving with it and our guide kept snapping away and we got this great action shot!

Also I have the best friends and I love how happy we look.

Komodo science: where the dragons came from

Huge thanks to our guide Ajis and his crew. Tourism in busy places can be a fraught affair, so do your homework and make sure you tourism responsibly by supporting local and sustainable.

Group shot!

Appreciating the other things

While I’m as much of a fan as charismatic megafauna as the next person, sometimes it’s the little things or the odd critters that bring the most delight and stick in the memory.

I was quite happy to agree to a suggestion from a very good friend that we go to Sri Lanka in the hope of seeing leopards and sloth bears, because who doesn’t want to see leopards and sloth bears?! And I’m so pleased we did go, because Sri Lanka was beautiful with amazing wildlife, and tasty (oh so tasty) food, and we did see leopards and sloth bears which lived up to their reputation as cute and cuddly love-to-see-them creatures. But when returning home and facing the inevitable question, “what was your favourite animal you saw?”, I didn’t even have to think about it. It was two things actually – the giant blue earthworm and the white-winged black tern.

Charismatic megafauna 1, kitty-cat (leopard), Yala NP, Sri Lanka

Charismatic megafauna 2, sloth bear cubs, Yala NP, Sri Lanka

(Sidenote: new frogs will always be the most favourite thing I see when on holiday or anywhere, but I think people get bored of that as my answer all the time, so in the interests of variety I’m going with something different here. If you want to see some of the frogs we saw, which were AMAZING!, check my Instagram.)

We saw the giant, iridescent blue earthworm (Megascolex coeruleus) in the rainforest at Sinharaja Forest Reserve. This fabulous, not-often seen creature, is spectacular enough to warrant mention on a favourites list. But I’m putting it at the top, because it was so unexpected. We’d had a creature-filled morning, with many endemic beautiful birds, several snakes, large lizards, small lizards, and pitcher plants, and I was feeling contented, thinking we’d covered a good variety of new and exciting things. Then we turned to head back to the guesthouse, and there it was – a one metre long, shiny BLUE earthworm! Who knew!? Completely new, something I didn’t even know existed, and just shuffling along without a care in the world.

As for why the the white-winged black tern was a favourite, that is a bit more complicated. When our guide identified the gorgeous, black tern I’d seen swooping for insects just above a small wetland at Yala National Park as a white-winged black tern, I found myself way more excited than I thought I’d be. While this tern shows up in the inland New South Wales wetlands where I work, that happens very rarely and I hadn’t seen it, and anyway this migratory species never shows its colourful breeding plumage in Australia, so it is just another mostly white-looking tern. But there is was! Something I’d heard of but never thought I’d see, and I was seeing it in breeding plumage! (Which, I realise could be the sentiment that outs me as a tragic-birder now…). It was just stunning.

White-winged black tern in flight (Photo: Mevan Piyasena)

So, my favourite non-frog animals are not just about looks, they come from a moment or a feeling or just a quirk. It is about appreciating the other things. Want to know more?

PS, I can’t recommend our guide from Sri Lanka highly enough, Mevan Piyasena. His itinerary was perfect for what we were interested in, and his knowledge of the wildlife and ability to make sure we were in the right place at the right time gave us the perfect trip. Don’t hesitate, just go and go with Mevan!

PPS. Want to know more about GIANT earthworms, check this article in Australian Geographic for information on the giant earthworms found in Australia.