Small things are eaten by medium-sized things, which are eaten by big things, which are in turn eaten by even bigger things. We tend to find it easy to imagine the animals at the ‘big’ end of the scale – lions, sharks, eagles, t-rex – but recently, I’ve been getting excited looking at the things at the ‘small’ end of the food-web. Specifically, what is the ‘small thing’ that tadpoles are eating?

Not all tadpole species eat the same thing. One species in the tropics eats unfertilised eggs that the mother frog lays specifically for them, it’s called ‘oophagy’. This recently discovered group of species does it and as does the vampire flying frog. Other species are notorious carnivores and cannibals. The Megophrys genus of species are so dedicated to eating the tiny things floating on the surface of a pond or stream, they hang suspended in the water by their peculiar upturned funnel-shaped mouth.

The common species in the floodplain wetlands of the Murray Darling Basin are not that kooky, but surprisingly there is very little information on what they are actually eating. Marion Anstis’ wonderful book notes that the barking marsh and spotted marsh frog feed on “vegetation and sediment, as well as available protein such as dead insects and tadpoles”. But I wanted to know more.

I got my chance as part of a project, funded by ILWS Charles Sturt University, aimed at understanding the food sources of these species using two methods, gut content and stable isotope analysis.

We collected up to six tadpoles from five different wetlands around the Murrumbidgee floodplain. For the first part of the work, I really didn’t know if I’d even be able to identify anything from my dissection of the gut. Fortunately, I had a high-powered microscope, and suddenly a world of ‘small things’ opened up.

I could see bits of invertebrates including zooplankton, beetle larvae and chironomid larvae, bits of vascular plants of various shapes, and long sections of filamentous algae (see below). Plus lots of mush. Even more fascinating was realising the tadpoles seemed to be ‘hoovering up’ items relative to how available they were in the environment around them. Where there was more zooplankton in the water, there was a higher number in the gut.

I’ve a sneaking suspicion that it is going to get a bit more complicated when I move on the results from the second part of the project. It may be that what I was seeing in the gut, may not be what is nutritionally valuable. I think that maybe even smaller things are going to be important.

I have a soft spot for uperoleias. Uperoleia is a genus of Australia frogs, which tend to be small, warty and generally unregarded. But I think they’re pretty fantastic.

There are a large number of uperoleia species, distributed throughout temperate, tropical and arid regions of Australia. They’ve had a rather complicated time with the distinction between different species being obscured by the physical similarity and small size of most of the frogs in the genus. That, and the remote location of most of them made getting the data to do comprehensive research rather difficult. It wasn’t until some rather detailed genetic work was recently completed that there was some certainty about which species was what and how many there were. Turns out quite a few – at least 28 species at last count, with most of them stomping about in the monsoonal areas of northern Australia (Catullo 2014 Zootaxa 3753 (3): 251–262).

I’ve been chasing Uperoleia laviegata around a bit recently, called the smooth toadlet. They have started calling around the wetlands at the CSU campus in Albury. Interesting wee fellows, as like most of the males in this genus they are calling from the long grass quite a way from the pond itself. The females pick the males they like the sound of and they make their way toward the water, which is where I found these guys.

The species I’m most familiar with from my fieldwork in the Macquarie Marshes is Uperoleia rugosa, the wrinkled toadlet. And here are three reasons why I think they’re just the best.

1. They have orange butts. OK, it’s more like orange pockets between the thigh and groin, but there is nothing more lovely than something that looks a bit drab and brown, flashing bright orange when it walks.

2. One of my fondest memory while living in the Marshes is grabbing a handful of these uperoleia from the lawn one rainy night, and showing them to the landholder, who despite living out there his whole life, had never see them before.

3. They fight! The males are territorial and will engage in wrestling bouts with other males they deem get too close. Not unusual behaviour for frogs, but not very common either (see these papers by Robertson, Given, and Duellman). They seem to be defending a calling site, as the territories are not where the eggs are laid or contain other resources. Basically, they reckon they’ve found the best calling spot and they’ll fight to keep others away from it. It’s hilarious, watching something the size of half my thumb get all huffy, hop about, grab another male by the waist and flip him. And if that move didn’t solve the matter, they’ll keep doing it until it did. It definitely made for a great entertainment one night in the Macquarie Marshes when after nearly 50 mm of rain fell, there were hundreds out, calling away and occasionally indulging in a spot of frog sumo (for the full story, read my short write-up on page 472: Ocock 2012 Herpetological Review 43(3): 472).

Taking friends frogging for the first time is really quite exciting. There can be such a sense of wonder and amazement that something making such a loud noise is actually quite a small beast. This is particularly apparent in the case of the Crinia froglets as my friend Dena, found last night. We had realised earlier in the week that while we’d indulged in Dena’s birding passion a few times, spotting superb parrots in Chiltern National Park and freckled ducks at Wonga Wetlands, I had yet to show her any frogs up close. Luckily, we both work at the Charles Sturt University in Albury which has a very handy, frog-friendly wetland complex located on campus. Due to the recent rainfall, frog calling activity as rife, with spotted marsh frogs (Limnodynastes tasmaniensis) and the eastern sign-bearing froglet (Crinia parinsignifera) dominating the airwaves, and a quieter undercurrent of southern brown tree frogs (Litoria ewingi) and the federally threatened Sloane’s froglet (Crinia sloanei).

I love getting to show people what the frogs they’ve been hearing actually look like that, to put a frog-face to the noise. It’s like a whole new world is revealed. I firmly believe that people care more about things they have seen and know about. So while for me this is a common little frog that I’ve seen and heard a hundred times, for others it’s a pathway to a whole new appreciation of some pretty awesome native fauna.

Once it was dark enough that Dena stopped focusing on the birds and concentrated on the frogs, we hunted down three species including the adorable Sloane’s froglet. I count it as a successful first frogging outing for her. We’re hoping for a bit of rain and warmer temperatures in the next few weeks, so we can tick some more critters off Dena’s new frog-list.

Speaking of exposing people to how awesome frogs are, it seems they are a popular theme for baby-things. My sister has been bombarded with frog-themed clothes and things for new brand-new little man, including this one-piece with hat, and none of it has been from me! We’re not sure if people are transferring my association with frogs to my sister or there is just a lot of frog-focussed paraphernalia for the newly-born. Either way, I don’t think it is a bad thing.