Using functional traits to identify conservation priorities for the world’s crocodylians: Podcast transcript

In this podcast for Functional Ecology, Assistant Editor, Frank Harris, sits down with Phoebe Griffith—a researcher from the Institute of Zoology, London, and the Wildlife Conservation Research Unit, Oxford University—to discuss her recently published paper ‘Using functional traits to identify conservation priorities for the world’s crocodylians.’ To understand better the functional diversity of crocodylians, Griffiths et al. collected a database of functional traits of all species of crocodylians. These traits are measurable qualities – such as skull shape or saltwater tolerance – that allow us to understand the different ecological role of species, and how similar and different species are from one another.

At the time of writing, this research is “in the top 5% of all research outputs ever tracked by Altmetric”.

The podcast episode

To find out about and support ongoing croc conservation efforts, please do check out the following links:


Frank: Hello, today I am really excited to have Phoebe Griffith with me. She is from the Institute of Zoology, and the Wildlife Conservation Research Unit at the University of Oxford. Today we are going to be talking about her paper— Using functional traits to identify conservation priorities for the world’s crocodylians. This paper is also due to feature in our upcoming Animal Functional Traits Special Focus. It’s great to have you here Phoebe!

Phoebe: Hello! Fantastic to be here and thank you for having me.

Frank: I’d like to ask you to tell us a bit about yourself, where are you from, what are your research interests? How did you get into ecology, and how did you then come to study crocodiles?

Phoebe: I’ve always had a huge interest in wildlife, particularly because I grew up in Nepal. I was therefore very lucky to see the incredible diversity of wildlife in the country. This then lead me to study biology. My particular interest is conservation because, inevitably, when looking around at the species I was interested in, I found that most of the ones that fascinated me—such as crocodylians and other freshwater megafauna species—were not doing terribly well. Therefore, I started this project that I am currently working on which involved working with partners in the Nepalese government looking at conservation methods for a species called the gharial. This is a very weird looking crocodylian! We started this project because the Nepalese government has been running a conservation project on the gharial for a number of years (since the late 70s). The population still remains critically endangered so there was a need for a science-based approach to understand the reasons behind that. This is how I first got involved in crocodylians and I have never looked back! Having started looking at a single species, that is what got me interested in a comparative approach, leading me to ask: why is this species so critically endangered when other croc populations have completely recovered from being endangered in the past? Looking at this group of species, we have this huge variation in extinction risk and conservation status.

Frank: I’d like to ask about the gharial in particular because that’s what started this journey for you. You talked about it being critically endangered—can you tell the listeners what has caused this? Is it anthropogenic?

Phoebe: Essentially, in the 1950s and 1960s, most crocodylian populations started being intensively hunted internationally for their skins. This was in a world post-WW2… There were a lot of men coming back from fighting who knew how to use firearms and had access to these new developments and technologies (motorboats and 4×4 vehicles). A crocodile’s protection is that it is very cryptic! They are very difficult to see; however, that is undermined as soon as you use a powerful electric torch. If you shine that in a wetland, they have this very reflective layer at the back of their eyes which helps them to see in the dark; but this means that their eyes shine just like cat’s eyes. From this point, it’s very easy to see where they are and kill them. Therefore, most crocodylians in the world had their populations really heavily hunted. At the same time—this is also quite difficult to disentangle from hunting—was the sudden big development projects such as damming and moving of rivers, and large-scale fishing. All of a sudden, with these habitat modifications, we saw big impacts on croc populations—they collapsed. With a lot of the hunted species, legal trade (which is still in place) came in so croc skins now are mostly collected legally which means there is very little pressure from an illegal trade. This means that most of the hunted populations recovered; however, the gharial did not. It seems that the hunting did not really impact the gharial, but rather the river modifications. In particular, the two big things that correlate with the disappearance of gharial and their inability to recover 50 years since has been the building of dams and barrages that are fragmenting the rivers they live in, and, the development of destructive fishing methods, I.e., gill nets which are nets made from synthetic fibres that entangle and drown a whole range of different freshwater species, including gharial.

Frank: Thank you for clarifying that. Another thing I would like to ask, because we are talking about the diversity and functional traits of crocs, relates to just how old they are. The diversity isn’t as prominent as the diversity you would see in birds or other long-living species that we associate with dinosaurs. Can you dig into that a little bit for me?

Phoebe: We are at a snapshot in time right now where there are very few croc species—probably around 28 at the moment. That number is changing as people look at the genetics and find that what they thought was a single species are actually populations that diverged millions of years ago, even though they look quite similar. What we are left with today is a sort of remnant of historical croc biodiversity. Even just a few million years ago, we had everything from the kind of crocodiles we have today, to completely marine crocodiles, and arboreal crocodiles (that could climb trees!). Potentially right up to a few thousand years ago you have species that would be fully terrestrial and run down their prey! Even if you go far enough back you have herbivorous crocs as well! So there has been this huge diversity in the past, and then generally, looking at the history of crocodylian forms, in warmer periods of history we see lots of diversity, and in cooler periods, like the ice age, you get this cutting down. Nowadays, you certainly have crocodiles retreating back to this perfect design of an amphibious predator that is perfect in form. There are always crocs like that because there are no other species that have nailed this amphibious-predator niche like crocs have. So, in a time where we have a low diversity (in evolutionary time), we are ending up with just sort of one basic type. However, in our study we were challenging the common conception that crocs and alligators are all quite similar. They are actually startlingly different even though they look similar to the human eye—they’re behaviours are completely different. For example, the Chinese alligator is a tiny little species which mostly eats molluscs, snails, and other hard shelled organisms like crustaceans. It digs these massive burrows to live in and can cope with very cold temperatures. At the complete opposite end of the scale, you have a 6+ meter saltwater crocodile that makes trans-oceanic journeys of hundreds of kilometres and can take down a cow if it’s a fully grown adult, as well as being saltwater tolerant whereas the Chinese alligator today is only found in freshwater habitats. Crocs don’t have the historical diversity we used to see, but they are still pretty diverse!

Frank: Fantastic! Just before we talk about the paper, I’d like to ask if you have any advice for any young budding ecologists and any tips & tricks of the trade!

Phoebe: It’s been said a million times, but definitely focus on doing what you love! My realisation of that was when I was doing an interesting project in Panama looking at entomology. I kept getting distracted because any time there was any crocodylian field site, I could sit for 8 hours trying to watch what the croc was doing and I’d end up 8 hours behind on what I was supposed to be doing! I wasn’t really getting far with my entomology career, but it made me realise that a lot of ecology is actually just spending a lot of time on a single thing, and if you don’t love that you can get very bored. So you should find the thing that you don’t have a boredom threshold for. Additionally, you should always talk and appeal to people! People in the field of ecology are especially great—almost every collaboration project I have ever done has just involved getting in touch with someone completely cold by just expressing admiration for someone’s paper and asking if they had any opportunities or whether they could help with project design. Ask everyone you can! Some reply, some don’t, but there’s no need to hesitate when asking for help!

Frank: Wonderful! Casting a wide net… always a good thing… except when you’re fishing in crocodylian waters, I assume… That’s really interesting because ecologists are stereotyped as people who got into the field via enjoying birdwatching as children and adolescents, so having grown up in an environment where you got to observe gharials and be in a really beautiful environment, it’s wonderful that you managed to channel that initial child-like wonder into building a career! Just before we start the next question, I’m very excited to say that Phoebe has brought some sound recordings for us, so perhaps she can just introduce what they are (without giving it away!) and then we can provide an explanation afterwards.

Phoebe: These are two recordings, that have kindly been shared with me, of two vastly different crocodylians. These are two of the species that got flagged in our analysis as being particularly unusual (I.e., having quite unusual ecological roles compared to other crocodylians). These recordings show two different crocodylians flirting!   

Frank: Wonderful, we’ll play that for the listeners now!

A gharial flirting with hisses and clicks
An American alligator’s bellow

Frank: Phoebe, can you please reveal what we were listening to and explain what’s going on?

Phoebe: Absolutely! The first recording was an adult male gharial, recorded by Jailabdeen A from the Gharial Ecology Project in the wild, in India. The gharial has this very unusual growth on the end of its snout in adult males. As they start to mature, this growth called the ghara gets bigger and bigger, and males that have this are able to make that percussive noise at the start of the recording—a pop! And Jailabdeen has been studying this and found that the pop is used for a variety of things like talking to their babies—they are fantastic parents—to threatening other males, to what we heard just then which was flirting with females. Those are the noises a gharial makes as part of his courtship routine. So, he pops up next to the female and makes that popping noise and then you have those kind of longer hissing/growling sounds he does while doing a sort of water dance to impress her! Generally the males spend a lot of time doing this, and, generally, they spend a lot of time getting ignored. However, very very occasionally, a female will be won over by this routine (or the 19th time she’s seen this routine)! It is absolutely amazing to see.

The second recordingthat kind of really deep, dinosaur sounding noisewas from Stephan Reber with some of the alligators from his lab. Stephan has a number of alligators that him and his team do work with to understand alligator intelligence and communication. The famous noise that alligators is make is this bellow. They are really deep noises that can’t often be heard by the human ear. In fact, the frequency is so low that they create these Faraday waves which makes the water dance on the male’s back which is really cool! Alligators bellow, so do some other crocodiles. In fact, most crocs are really chatty—they spend a lot of time communicating with each other, particularly for courtship, and both males and females make these kinds of hissing and bellowing noises. We are only just starting to understand exactly what these mean, essentially by eavesdropping on them!

Frank: Fantastic! I think how vocal they can be is something that most people are unaware of (I certainly was). So just for a bit of fun, regarding the dances and sounds, do we know what could potentially separate the wheat from the chaff? What makes a good dance or sound? Is there a barometer?

Phoebe: So Stephan, who shared the alligator recording with me, did a pretty fun study where his team were looking at how size of alligators impacted the sounds that they could make. I.e., bigger alligators were able to make deeper noise, which is representative of an honest signal to females that they are the biggest and the best, you should mate with me! So Stephan’s team gave these alligators helium so that they could make higher and more perceptible noises. The results suggested that the sounds demonstrate size and power to females, which helps to communicate the quality of a male alligator’s genes, it’s potential to defend territory, and that they can be a good parent to a female’s offspring. Particularly for gharial, bigger males that develop bigger gharas can make these louder pop sounds. This is important for gharial because the males play a really key role in parenting, so a big male is going to look after all of the female’s babies and do a really good job. There is barely anything that could threaten a big male gharial (~6 metres), so by picking the biggest and best male, the female has a better chance of her hatchlings surviving. These are the ideas that are being bandied around at the moment, but it’s still an area that needs more research.

Frank: That’s so fascinating. Well lets get on to the paper now. Can you please, in plain terms, explain the novelty of your paper? What does it contribute to our understanding of crocodylian functional traits, and how does it advance our understanding of how to conserve these species?  

Phoebe: So crocs are pretty hard to study in the wild—they are very hard to find and cryptic, they spend a lot of time underwater, and a lot of species can be quite dangerous if you are unlucky. So, this technique was primarily developed by botanists. We used a functional traits approach, I.e., measurable traits. In the case of crocs, these are things like male and female maximum size, reproductive parameters, a measure of skull shape, different types of habitats, whether they can move over land, etc. By collecting all these traits for every individual croc species, we can put them together and estimate the ecological role of each species. A species that can’t travel over land and has a really long, thin skull, only found in very specific aquatic habitats, is going to have a very different ecological role to a species that spends half of its life on the rainforest floor that can be found anywhere and has a short, stubby skull which is more capable of a generalist diet. By doing this, we were then able to quantify the differences between species’ ecological roles—and their similarities. We could find clusters of these functionally similar species, not necessarily closely related ones, but ones that were likely to be performing the same ecological role in their environment even if they were found on different continents. Also, we wanted to highlight species that were completely unique—there’s nothing else quite like them! So, in particular, the number one species was the gharial. There are no other croc species that pop at females, have these massive communal creches, that grow to these massive sizes whilst only eating fish and other aquatic prey. This then enabled us to quantify these groupings and differences. This could then be useful to inform how we study crocs and their roles, but also how to conserve a given species. As part of that, we highlighted the most unusual species that are also at a really high risk of extinction. These are species with an irreplaceable ecological role—if we let them go extinct in the wild, there will be nothing left like them on earth.

Frank: Thank you for that. To follow up, in the paper you identify key species for conservation action as well as discussing how complementary those selections are with other types of conservation prioritisation. How does that translate to on the ground recommendations for conservation.

Phoebe: One of the big questions in conservation is the fact that there will inevitably always be a limit in resources; therefore, how do we prioritise which species funders or organisations should focus on? We can’t focus on everything, sadly… So, we flagged these functionally distinctive species and asked: how does this tally up with the other ways people have been prioritising species? Are we wasting our time looking at all these different aspects instead of using one quick and easy measure? The one we were particularly interested in was phylogenetic diversity—the diversity of the Tree of Life—and a measure called EDGE (Evolutionary Distinctive and Globally Endangered species). These are species that represent a whole branch on the Tree of Life—often only represented by one or two species that are at risk of being entirely lost. What we found that was very interesting was that the loss of these species—that are evolutionary distinctive (weird without any close living relatives)—lined up with the same species that were having these unique functional roles in their given environments. There was a lot of complementarity so these schemes, like EDGE which focuses on conserving these unique evolutionary species, are also doing a pretty good job at capturing a lot of the species that are likely to have an irreplaceable functional role. However, we did not find that this was always the case. On the other end of the spectrum, we had a lot of functionally unique species that had a LOT of close living relatives and had this sort of speciation in relatively recent evolutionary years. Particularly, true crocodiles—the big group of crocs that are synonymous with the word, only diversified around 10 million years ago, but they are on every tropical continent of the world. We found that a lot of them were very unique and this has been driven by recent evolution pushing species to evolve more quickly. In terms of practical recommendations, when you are able to measure functional diversity, that is very useful; however, where it is not possible, looking at the Tree of Life is a pretty good proxy measure.

Frank: The last part of this question is related to the fact that your team identified Asia as a hotspot for threatened croc species. We’ve already spoken about dam and river manipulation as a key problem for croc species, but based on the information in your research, what can be done to facilitate the conservation of wetlands and river ecosystems in Asia to protect crocs? Is it about relocation, how do we do this given the fact that we have irreversibly changed these landscapes through dam and barge projects?

Phoebe: All populations of crocodylians in Asia are threatened in some way. Because of huge impacts on rivers, almost everything, if we think about so much of human society worldwide, focuses on rivers. Therefore, they tend to be the most impacted part of our systems due to anthropogenic impacts. This is especially true for areas where you have a lot of fast development happening. This results in huge amounts of pollution, over-exploitation, removal of species, etc. Another thing about rivers is the fact that it is a connective system—what happens upstream is going to have knock-on effects downstream. All over the world, but especially in Asia, we must think about the river ecosystem as a whole as something that must be conserved for the sake of biodiversity and, equally, human health. These rivers are often so important for river-dependent communities who sadly can often be marginalised and not considered by large-scale infrastructure decisions that are being made at the international level. We must think about the river as a living thing that we want to conserve for biodiversity and people—not just as a source of hydroelectric power or irrigation. We need to see a big shift to focusing on conserving the whole river system and all the different parts that make up that ecosystem. We don’t know what impact it will have if there are no more crocodiles, or large fishes, or river dolphins, but it is likely going to be negative for the functioning of the river or wetland system. With climate change and unpredictability of weather, natural nature-based solutions to managing flood risks, such as wetland restoration, will be very important. Inevitably, if that’s happening in Asia, the restoration of wetland and historical species will require the reintroduction of crocodiles as they are no longer found in most places they have historically have occupied. This is an exciting opportunity, but it is also a very big challenge.

Frank: I wanted to talk about the germination of your study idea, and why you felt compelled to share this with the ecological community, but I feel like we may have covered this already. Is there anything else you’d like to say on this or talk about?

Phoebe: Just in terms of the germination, the paper came about from working in Nepal, where you have the gharial but also the mugger crocodile. These species coexist in the same environment. We were there doing our project on gharial, but at the same time we were seeing mugger populations recovering very well without much of a conservation effort. This made me very curious and set the ball rolling for thinking about differences between species. People would talk to us about mugger footprints being found in the middle of the jungle, in the dry season and miles away from the nearest body of water! One of the wardens even told us about muggers walking on highways! Conversely, gharials can’t get out of the water very well and they can’t walk like other crocs on land. This is how I started thinking about just how different these ostensibly similar species could be, and it just snowballed from there into looking at every croc species!

Frank: Well it’s a wonderful article. Before I move on to one of the last questions, I’d like to point out the Edge of Existence blogpost that you and your co-author, Rikki Gumbs, produced. It’s got a great title—Crying Crocodile Tears: The disappearing diversity of crocodylians and their ecological roles. I found it to be a wonderful resource for learning about your research. It has amazing pictures of different crocs, crocs that you couldn’t even dream of conceiving—the shape, size, body types… It’s remarkable! A link to that post will be made available in the description of this podcast so that the listeners can check that out.

So, finally, where do you think the research should be moving towards next?

Phoebe: From our paper, there are two main recommendations for moving forward. The first says that these crocodiles have very different ecological roles and we must call for more research into these differences. We have to try and understand how it is that crocs, as these huge predators in these systems, are involved in ecosystem engineering or nutrient management/cycling. Different processes have been investigated quite well in terrestrial or marine predators like wolves or orcas, but crocs haven’t yet had that level of field research, so that’s a really exciting and challenging ecological question. The other recommendation centres on applied conservation. It says that this is urgent. These species are disappearing and many of them already gone from most of their former range—their not totally extinct, but their not performing these ecological roles in 98–99% of their former range. We must call for more conservation action, and more applied research to understand what interventions do and don’t work. Then we must share this Open Access with everyone so that everyone can take part in the effective conservation of these species.

Frank: In Nepal, can you see action happening on the ground? Has the ball started rolling?

Phoebe: Absolutely! The Nepalese government and Chitwan National Park set up a conservation programme back in the 1970s. It was a trailblazing conservation programme due to its focus on a reptile rather than a charismatic species like tigers or rhinos. The wonderful thing we found with the research that we have been doing—the science and ecology to underline and understand why some of these conservation interventions don’t work— is just how interested everyone has been—NGOs, national park staff, etc. We have shared all of our data and results with them. This means that they can immediately think about how to bring about positive changes. For example, we suggested that they should release gharial further upstream as they would have a better chance of surviving their first monsoon and this was tried this year! In addition to this, we like to share the audio recordings and videos of the fantastic parental care that gharials do with interest groups and local communities because these are their gharial living in their rivers. It’s just wonderful to see these community-based groups setting up their own gharial conservation work or asking where the research is headed towards next and how they can help/lead with that. When they do this, we think to ourselves: this is your river, this is what we’ve learnt, and you should run with it! It has been very positive and incredibly uplifting.

Frank: Amazing news. I don’t want to bring it down too much, but I’d like to you get your crystal ball out for me and describe what the future looks like at present for crocs. One thing I wanted to know about is the fact that crocs throughout history have re-diversified and bounced back from 2 mass extinctions in the past… Is there anything unique about the Anthropocene which might mean that their characteristic resilience might not be enough?

Phoebe: What’s going on in the Anthropocene is so different from anything we’ve seen historically that comparisons are almost moot. In the most recent extinction, which wiped out the dinosaurs, crocs didn’t have much of a problem dealing with it. A big part of that is that they are predominantly a river-based species. River systems are generally driven by detritus. When the world is ending around a river, and all that dead matter is ending up in the river, the river is the best place to be! In a way, those rivers were a sort of refuge—crocs in rivers were safe and prey/food was prolific. They also dig massive burrows—the biggest burrows currently dug in the animal kingdom are dug by crocs! Therefore, they can also hide away in these burrows when it’s cold or inhospitable. However, we are seeing a complete opposite today where threats such as pollution and removal of water are all centred on rivers. Instead of being safe spaces, rivers and inland coastal areas are now the most impacted places… The question now is, are crocs going to be able to survive current levels of impact before these systems can hopefully recover. Think about the wetlands in the UK! So many have historically been drained, but we are now starting to restore and rewild them here. However, if it takes us that long to start restoring wetlands in other parts of the world, it’s very challenging to know how crocs can possibly cope. But, a lot of species are pretty resilient. The fact that the Chinese alligator isn’t extinct is mind boggling! It lives in the most impacted, hyper-agricultural areas of China, and yet they are still there… Only a few… but they are there in the edges of fields and duck ponds. If the species can hold on, then there is potential to reintroduce them to certain areas in the future. There is also a lot of history surrounding crocodiles. Lots of cultures have stories and they have a lot of cultural and folkloric significance. A lot of people want to conserve crocs and are interested in them which is a huge asset for our conservation efforts as ecologists.

Frank: That ties in to my last question actually. Aside from the ecological roles identified as a key aspect of crocodylians conservation, why do you think the conservation of crocs is so important outside of the ecological purview?

Phoebe: I just love them. I think they are very fascinating animals, and, from growing up as a child, I have always thought about those species that have already gone extinct because of human activity. That always made very sad and angry as an 8-9 year old. I really wanted to see the Baiji (Yangtze river dolphin) that had just gone extinct, or these other species like the Thylacine that people continue to have mass interest in. If we lost croc species, we are losing something that is, on the one level fascinating, and on the other a vital thing associated with culture and folklore. For some people, certain crocs are totemic, for others there are lots of beliefs that crocs are our ancestors. In other places, they are important to folklore and storytelling. Work on other species has shown how a lot of these beliefs are really important for understanding our own cultural history as humans. If we lose crocodiles, we don’t only lose their ecological role, but also their cultural role.

Frank: Indeed. They’re one of those animals that really inspire children, and I think that their power and animism is so symbolic as a touchstone. If they were to go, it would be a loss or absence that would be very strongly felt.

Phoebe: There are certain species we will never lose. I.E., American alligators, Nile crocs, saltwater crocs. But, some of these more unusual species are the ones that are at risk. It will be a real shame if we are only left with one type of croc rather than the diversity we currently have.

Frank: Well, as you have shown, there’s still hope yet! Just to wrap up, is there anything else you’d like to say? Any thanks to collaborators or contributions? And any take home messages for our listeners?

Phoebe: A huge thank you to everyone who discussed this paper with me. There were dozens and dozens of people who put up with endless emails about what they’d seen in their field sites or if they’d seen a certain croc species. Huge thanks to everyone who answered my endless questions! To leave, I would encourage everyone to find out more about these weird species of crocodile, and, if you can, to support conservation efforts. There’s some really incredible research and conservation work by people who work with some of these more unusual crocodiles. Find out about what these groups are doing and support them to conserve and protect croc diversity!

Frank: Thank you. A link to the paper will be available in the description of this podcast. As I said, it’s due to come out as part of an upcoming Special Focus on Animal Functional Traits in a few months’ time. I’d like to really thank Phoebe for her time. It’s been fascinating discussing this with you and I really do wish you the very best of luck with your conservation efforts and I hope we’ll have lots more positive things to talk about in the future.

Phoebe: Thanks for having me on and letting me whitter on about crocs!

Frank: Anytime, thanks so much Phoebe.

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