An explosion of breeding frogs

What sparked your interest in this mating event? 

I’ve always loved amphibians – it’s always been my thing! Frogs, toads, newts and salamanders. Ever since I was really young, I think that was one of the main things that sparked my interest in nature and wildlife was looking at the frogs in my pond during springtime reading! When I knew that we were making a series about mating strategies, I was like: "Right, I’ve got to get in as many amphibian stories as I can!"

Nancy rang up Austrian scientist and herpetologist Walter Hödl to learn more about some of nature’s most exciting examples of amphibian breeding. And they began chatting about explosive breeding. But what actually is it? 

An event like no other... 

Explosive breeding is basically when in an area that’s been relatively dry, when there’s a big period of rainfall, these kind of temporary ponds can form and it’s also typically in Europe with warmer weather in the spring – and loads – hundreds, and sometimes thousands of amphibians will gather in this one water source over the course of a day or two or a week to breed.

After discussing the breeding plight of moorfrogs, and other amphibians, Walter had an idea. He assured Nancy that he’d been to the Serengeti, Antarctica, and all over South America – but this particular event was the most incredible wildlife spectacle he’d ever seen. Thousands of raining frogs journeying into one singular pond, including a plethora of different species. And only a handful of people had ever seen this event in the past. Typically, it only happens for 1-2 nights a year between November and February. So timing was everything.

What was the most memorable moment? 

So we were in the jungle, and it’s Christmas, and we kind of joked all along - is it going to happen on Christmas Day and we thought there’s no way it’s going to happen it would be too coincidental – but that’s exactly what happened! This pond had formed from the rain – that had happened in the last two weeks before Christmas […]  we were going in to check what was going on […] the frogs had started to come down – so we kind of ran out and got all of our gear. We ran out and we were there for about 12 hours filming and I can’t even describe what the noise is like – it’s deafening. So you can’t be within 10 metres of the pond without wearing earplugs.

We all had earplugs in throughout the whole night, you know because you’ve got up to six different species and thousands of them calling as loud as they possibly can to try and attract a female – and some of them have these vocal sacs that come out and touch above their head – and when they call it  sounds like a ‘rrrr!’ noise. 

We were all sort of completely delirious because we’d been awake the entire night, and it’s as if you’ve been in a night club, because your ears are ringing from the sound. So, we all wandered back to camp, just feeling so pleased that we’d managed to get the sequence and we sat down, and we had some cake, and we had a glass of champagne!

In the lead up to filming the main event, the team also made some other extraordinary discoveries... 

We filmed these beautiful tree frogs called Dendropsophus counani – that lay their eggs on a leaf. They do this before the heavy rains arrive, in the knowledge that eventually the eggs will drop down in this kind of jelly sac and you can see the tadpoles wriggling in there. But they then eventually fall into the pond that then forms – so the frogs are aware that the rain’s coming.

 

What challenges did the climate pose? The water itself must have been a big issue! 

That was 100% one of the biggest challenges – and something we spoke about a lot! How we were going to manage it […], keep everything dry […] how we were going to keep ourselves dry. The ponds that filmed in were about waist deep – so we had [to use] rubber waders. We’d also heard that there was a resident electric eel in one of the ponds, and when we arrived the pond was completely dry – there was maybe a tiny puddle of water on the ground – and we saw the head of the electric eel pop up. And that was then the pond that flooded that we filmed in! So we knew that we were kind of in there with an electric eel, and we had rubber chest waders on as a kind of safety precaution.

As Nancy confirmed – electric eels are pretty dangerous to humans!

How did you keep all of the camera equipment dry? 

We were very, very lucky on the night that it actually happened. There had been this big period of rain up until the event and on the night, it stayed pretty dry, and it was dry for most of the night. In our trail runs we had giant golf umbrellas and big see-through polythene plastic bags. We kind of fashioned ways of getting over the camera that you could kind of pull up underneath and film just keeping the lense exposed, so a lot of giant plastic bags and big umbrellas was kind of how we did it! Then we had this whole system back at camp, because also where we were staying was completely out in the open. We had a roof, but no sides to where we were staying – so everything was just incredibly damp and humid.

Nothing ever dried – so we had wet clothes for a whole month! And anything you took that was leather […] grew mould – my leather birkenstocks grew a layer of mould! We’d have pelican cases which are the big cases that the equipment comes in just full of silica gel which is that super absorbent stuff that absorbs wet moisture and humidity – so we put the cameras into this kind of dry box with the silica gel to help keep the lenses clear of fog and help keep everything dry – so that was our system. It was very tricky!

Nancy explained that due to basic facilities, you risk getting company whilst having a shower... 

You’d have to go down onto the pontoon and just kind of leap in and have a wash, and get out again. They told us that there was a 9-foot anaconda that used to live under the pontoon – and I thought they were joking – but then one day I did a boat journey – about 100 metres upriver – and we saw the very anaconda lying on this log by the river – and it was really like that – and they were like ‘oh yeah that’s the anaconda that used to live under the pontoon!’

And how long did the breeding event go on for? 

The whole event was about 13 hours. But I think they would come and go and different times, and obviously for the males they’ll just try and win as many females as they can, and the females will lay their eggs, and maybe the females leave. But so much is unknown about it, because it’s only been seen a couple of times. There’s a huge amount of science research that could be done off the back of these questions.

And for me, that’s a really exciting prospect - that there could be loads more of these ponds that we don’t even know about. I hope [this event] might inspire some more research. It’s personally something that I’m really interested in.

The Mating Game explores the animal kingdom's spectacular quest to find a mate. For more information, visit our show page. 

Featured image © Jack Hynes