- Endangered western leopard toads have lost habitat to urban development in Cape Town, and crossing roads during breeding season adds another danger: getting “squished.”
- Mongabay interviewed Andrew Turner, scientific manager for CapeNature, who discussed underpasses to help the toads safely reach their destinations: ponds for mating and laying eggs.
- Citizen science offers a useful data source, as volunteers record and photograph the toads they help cross the road; “It’s hard for scientists and researchers to be everywhere, but citizenry is everywhere,” Turner says.
CAPE TOWN — Western leopard toads have been listed as endangered since 2016. Andrew Turner, scientific manager for CapeNature, the government body that manages protected areas and conservation in South Africa’s Western Cape province, says the species was once more widely found across the Cape Peninsula as well as Kleinmond, Betty’s Bay and the Agulhas Plain. But over the last 20 years, much of its habitat has been lost to urban development, though no quantitative data exist.
Leopard toads spend most of their time away from water, but during the breeding season, from late July until September, the amphibians need to reach ponds where they mate and lay their eggs. In an urban environment, this now requires them to cross busy roads.
“Roads and toads are not a great combination,” Turner told Mongabay. “A lot of people don’t see them, or are traveling too fast to avoid them, and then you end up with squished toads.”
Turner spoke to Mongabay in Cape Town. This interview has been lightly edited for clarity.
Mongabay: Western leopard toads are threatened because of extensive habitat loss in the past two decades. Has that stabilized now?
Andrew Turner: So, I wouldn’t say it’s stabilized. Habitat loss has continued, but it has obviously decelerated a lot, because over time, the opportunities for further development have declined. There’s not that much natural habitat left that can be developed, so applications for development that do happen within the western leopard toad’s current distribution will require that authorities check that it isn’t an important habitat for the species.
Mongabay: What toad conservation initiatives have been successful in the Cape Town area?
Andrew Turner: That’s a difficult thing to say. There’s a couple of initiatives. One is the people who assist the toads to cross the road. But it’d be very difficult to measure that effect versus if you didn’t help them cross the road. It’d be a pretty difficult thing to do to measure the mortality in two different ways. And the same goes for the second initiative, the underpasses that have been put in.
Let’s deal with the underpasses first. Nature Connect and their partners have been putting in video cameras to try and get an idea of whether the toads are using these underpasses, and to what degree.
The trouble with that is to actually analyze the camera footage. Toads aren’t the easiest things to pick up [on camera], and they’ve now got a lot of data. They’re looking at various analytical techniques, probably involving some machine learning, to try and automate the detection of the toads in the footage. So that’s a bit of an ongoing project, and at least that’ll give us some measure of the degree to which the toads are using the underpasses.
And then you can also look at improving the design of the underpasses to try and make sure that more toads use them, which you can achieve by putting up drift fences on either side so they’re kind of funneled into the underpasses rather than trying to cross over on the surface of the road.
The other way you can get a grip on whether the population’s in a good shape or not is to look at the genetic diversity and how that changes over time. There are ways of calculating the effect of population size from genetic diversity. Instead of counting their numbers directly, you look at the genetics and infer from that how well the population is doing. That’s probably the most practical way — not the easiest way, but the most practical way — of getting some insight into how well the population is doing.
So, some of that work has been done, and over the course of time, we can track that. You might not establish right now whether the population’s OK, but if you can keep comparing diversity indices and population estimates from those methods over time, you can get an idea of whether the population is maintaining its diversity or whether it’s slowly being eroded.
Zooming out from Cape Town a little bit: There are populations of western leopard toads outside of the city, on the Agulhas Plain [roughly 230 kilometers or 130 miles southeast of Cape Town]. But the interesting thing is that from a genetic diversity point of view, those populations aren’t doing particularly well either.
So, from a species point of view, the Cape Town population is actually very important, because despite all the pressures on it, it is still harboring a lot of the genetic diversity that the species has. So, it’s almost doubly important to make sure that we look after the Cape Town populations — without forgetting about the Agulhas ones, which probably also require some attention to make sure their habitat stays intact, at least enough for them to carry on living in and breeding.
Mongabay: Are the toads in the Agulhas Plain facing the same threats as the Cape Town population?
Andrew Turner: Yes, there is ongoing urbanization, especially in the coastal area. At least on the Agulhas Plain, they do occur a little bit further inland. But then, things like invasive alien plants are a bit more of an issue down there.
Mongabay: How are alien plants an issue for the toads?
Andrew Turner: Well, it changes the structure of their habitat completely. If you get an area that’s invaded by Port Jackson [Acacia saligna], which is one of the major invaders down there, it becomes a dense woodland, and that is not what the toads have evolved to live with.
And then there are two other knock-ons. Firstly, those alien invasions certainly use more water than the [native] fynbos [shrubland]. And secondly, invasive vegetation can lead to some really high-intensity fires when the fuel loads from these dense growths of invasives go up in flames. Fire itself is not a bad thing. It’s actually great for maintaining fynbos, but it’s the nature of the fires that one needs to consider.
So those two things, working in concert, are probably not great for things like western leopard toads.
Mongabay: Coming back to the volunteers who help the toads cross the road. You said it’s difficult to accurately measure how much of a difference that makes.
Andrew Turner: Well, you can logically deduce that if you are preventing toads from getting squished in the road, you are giving them breeding opportunities. So, the effect is very, very likely to be positive.
It’s just the magnitude of that positive effect that is not well-known at this point. It’s not easy to compare numbers in areas where the toads are being helped with areas where they aren’t. And I think that’s where the genetic approach is probably going to be a far better thing for long-term monitoring of this particular species.
Mongabay: I shadowed two people who helped the toads to cross the road. When they found a toad, they’d help it across, take a picture of it, measure it and upload the data to iNaturalist. Is citizen science like this useful for ongoing toad research?
Andrew Turner: Yeah, I think increasingly things like iNaturalist are becoming really, really useful sources of data. It’s hard for scientists and researchers to be everywhere, but citizenry is everywhere, and I think more and more people are becoming interested in that, so it does become a nice repository of data.
It may not be as systematic as a formal survey, but that data is captured and is there for future research, sort of looking backwards. We might be able to do more with that data in future using some of the sort of more automated analysis tools that are being rapidly developed, so that data is likely to become more and more valuable.
It’s certainly going to put us in a position where we know more than if we weren’t collecting that data. So, I think that’s a great initiative. Basically, the more the better.
Banner image: Philipa Clemo and her friend on Zwaanswyk Road in Tokai. The pair are among the volunteers who help leopard toads across hazardous roads during the breeding season. Image by Barry Christianson for Mongabay.
The frog that wasn’t there: Survey shines a light on Uganda’s amphibians
Feedback: Use this form to send a message to the author of this post. If you want to post a public comment, you can do that at the bottom of the page.
Credits
