Blog post archive

Welcome to the No Free Lunches blog! These posts follow the work of Gabriella Leighton, a Master's student at UCT, working with the Urban Caracal Project to understand how urbanisation affects the diet of Cape Town caracals. Here is an archive of previous posts:

Of mice and museums

The past week has seen me back at the Iziko South African museum in Company’s Garden in town. It was a rat-run, pun intended. In my previous trips I was working with Graham Avery on identifying bird and larger mammal bones. This time around I met with his wife, Margaret Avery, who is an expert on micromammals (this includes rodents) and specifically studies the Cenozoic period. What this means is that Margaret is very good at recognising very small mammal species by looking at their teeth and cranial bones. The couple has been working for the museum for a long time and they are now emeritus associates. Despite ongoing renovations and constant moving of offices and collections in the museum building, we managed to book the lab for two days last week and one day this week – just before and after the big storm hit Cape Town!

What I’ve been learning over the last few months is that there are some really interesting micromammals right here on the Cape Peninsula. By far the most common in my samples have been African vlei rats, which belong to a genus called Otomys. What I didn’t realise is that there are several species of Otomys in this area. The two species we’ve found so far in the scat samples are Otomys irroratus (this comes up a lot) and Otomys saundersiae (aka Otomys karoensis), which co-occur in the Fynbos biome of the Western Cape. Otomys irroratus is associated with mesic grasslands, but according to Margaret the smaller O. saundersiae can be found in rockier, higher altitude areas. These species are exclusively herbivorous, mainly eating grasses.  Interestingly, they aren’t typical rodents in that they usually only produce one or two offspring at a time, which are born precocial, erupted incisors at the ready.

Rhabdomys pumilio, or the four-striped grass mouse, is another fairly common small rodent player in the Cape Town caracal diet so far. There have also been some remains of incredibly tiny African pygmy mice (Mus minutoides), grey climbing mice (Dendromus melanotis), Namaqua rock mice (Micaelamys namaquensis), African marsh rats (Dasymys incomtus) and brown rats (Rattus norvegicus). The latter species is closely associated with cities, yet we have found only a few instances of it becoming dinner. Even more surprisingly, we did not find any remains of house mice (Mus musculus). It is the most numerous species of the genus Mus globally, although originating in northern India, as they have spread with humans all over the world. House mouse phylogenies have even been used to reconstruct early human movements. Given that they are very common in urban areas, as they live in houses, I would have thought we would see them in the caracals’ diet.

Bigger rodents like grey squirrels (Sciurus carolinensis) and mole-rats have also featured. The Cape mole-rat (Georychus capensis) is quite distinctive, with russet-coloured fur and a silvery-white underbelly. Like most mole-rats they live in underground tunnels, rarely emerging to the surface, and they are nocturnal. However, unlike some other species, they are solitary, except when raising young, and are extremely aggressive to intruders. My discovery of the Cape dune mole-rat (Bathyergus suillus) in a scat was confirmed by Margaret, and we found quite a few more samples containing evidence of this species. I was very interested when we found some gerbil teeth! The Cape gerbil (Gerbilliscus afra) is a nocturnal rodent endemic to the Western and Northern Cape, South Africa and is found in sandy soils in which they dig complex tunnels. Despite its adorable appearance, it is often considered a pest during population explosions, as it is well adapted to agricultural fields. It’s fascinating to consider that this species has persisted while surrounded by such built-up areas.

We found quite a few non-rodent micromammals too. So far there have been three species of shrew: the reddish-gray musk shrew (Crocidura cyanea), greater red musk shrew (Crocidura flavescens) and the lesser dwarf shrew (Suncus varilla). We have also found a few instances of golden moles – which were further identified as the Cape golden mole (Chrysochloris asiatica). This is an insectivorous mammal with short, iridescent fur, no external eyes and large digging claws, which is widespread in south western South Africa. Its populations are not in decline and it seems to adapt easily to urban areas, and has become the bane of many gardeners.

While going through all the samples, I made sure to group those scats found in the same GPS cluster – just to check whether the remains belonged to the same individual or not. Margaret can tell this by looking at left and right-sided bones (especially jaws) and the number of upper and lower teeth. It seems like the caracals like to snack on more than one of these smaller prey items at the a time, as most of the scat had several individuals or several species present in one sample.

The broader patterns in the scat and kill data are beginning to emerge. Once I have all the identifications done (there are still a few that need to be done purely on the basis of microscopic hair scale patterns), I’ll begin to analyse the data properly, but for now I can see that most of the prey base is made up of wild species, rather than introduced ones. While I can’t say much about prey preference because I don’t have records of prey abundance for micromammals on the Cape Peninsula, it is still interesting to see that the caracals aren’t necessarily focusing on synanthropic (i.e. human-associated) prey. The southern cats nearer to Cape Point seem to eat more birds (especially Cape cormorant), while rodents make up the bulk of the diet for the northern and Noordhoek wetland caracals. So far, it also looks like female caracals take more avian prey than males do.

I found my time at the museum engaging – it’s wonderful being able to work with people who are so dedicated, knowledgeable and enthusiastic in their field. I’ve learnt plenty and I’m very grateful to the Avery’s for all their help, which has yielded some very interesting findings!

When predator becomes urban caracal prey

I’ve been sorting out the caracal kills database over the last few weeks, filling in missing information and looking through photos of kills that never made it to the freezer for closer inspection. It can be tricky identifying a half-eaten prey item when you have it right in front of you, but this becomes much more challenging when all you have is a blurry photo. Around 80% of the kills are birds, so usually this involves identifying feathers. For the most part the feathers are pretty easy: unmistakable spotty and black for guinea fowl, or greenish, brown and white with fluffy barred down for Egyptian goose. I breathe a sigh of relief when I see these. However, there have been some really difficult feathers to figure out, and quite a few frustrating ones which I’m pretty sure we’ll never get. Investigating the diet of a cat that seemingly eats anything, in a city with all sorts of introduced animals means that its hard to rule out even the strangest prey candidates. Along with domestic cats, goats and sheep, there have also been peacocks, domestic chickens, geese and ducks…

Some of the most fascinating cases concern birds of prey. Its intriguing to consider that the tables can be turned and the hunter becomes hunted. The first case of this I came across was the Rock Kestrel (Falco rupicolus), unexpectedly revealed as a late evening snack for Protea (TMC24), one of the southern Peninsula females. Luckily, these feathers were collected so we could look at them carefully. This species is known to breed in the Cape Point area, occurs widely in many southern African countries and is common in South Africa, particularly, as the name suggests, in mountainous or rocky areas. They are known to hunt in open areas, and pounce on their prey from the ground, and take a variety of species, from rodents to rock pigeons to reptiles and insects.

I then heard of another case of hunter turned prey in Wilderness, South Africa at the end of last year: a Black-headed Heron successfully nabbing a vlei rat, only to be taken by a caracal a few seconds later. This amazing scene played out in front of Kelsey Green’s camera lens, resulting in some amazing photos. So it’s very possible that this Rock Kestrel was distracted enough in its own hunting endeavour to fall prey to a hungry caracal.

Since then, I have discovered some more instances of raptor-cide. The next was an opportunistic kill found in the Noordhoek wetlands. Sadly, the only evidence I had was some photos of a mangled carcass taken in very dappled light, with the feathers fairly obscured by leaves. I could tell that the feathers and head belonged to a bird of prey, I just couldn’t be sure as to which one. So I sent them to Jessleena Suri, who has been fantastic in helping me identify bird kills in the past. She also has an interest in urban ecology, as well as ornithology, and has plenty of experience with this kind of thing, as she did her Masters on urban Black Sparrowhawk (Accipiter melanoleucus) diet in Cape Town. That project has some really interesting results. She rose to the challenge, and managed to pin down the unfortunate bird as a juvenile Jackal Buzzard (Buteo rufofuscus). This species is much larger than a Rock Kestrel, and the juveniles look quite different from the adults, as they are mainly brown above and rufous brown below and on the tail feathers. It can be quite problematic differentiating buzzards, but I’m pretty confident in this identification.

The last case I found while going through some more photos taken at clusters. I wasn’t given much to go on, as the (single) photo was blurry and the feathers were covered by vegetation, but once again I could see I was looking at something different. After some consultation with Campbell Fleming, a professional birder (and convenient office-mate), and a useful feather quiz by Faansie Peacock (see Question 3), I’m pretty sure these belong to a Spotted Eagle Owl (Bubo africanus). This species is much more commonly found in urban areas, like Tokai where these feathers were discovered, than the Cape Eagle Owl (Bubo capensis). This kill was made by one of the juvenile male caracals, Strandloper (TMC21), perhaps getting experimental with his meal choice.

These cases highlight to me that nothing is ever certain, especially in this urban jungle! You could very easily be hovering at top of your food chain and the next day be caracal cuisine.

“Oh look, another cape cormorant”: some trips to the museum

The last few weeks have been spent preparing samples for further identification by bone. This involved carefully sorting through each cleaned and dried scat sample to pick out the hard bits (i.e. bones, teeth, claws and nails) and package them separately. This makes it easier for comparison to reference skeletal material. Next, I decided to reorganise the samples according to prey group by date: rodents (the large majority!), other mammals, birds and reptiles. With all my samples neatly packed and organised they were ready for a trip to the museum!

I was very excited to have (finally) organised a meeting with Graham Avery, a retired museum curator and archaeozoologist at Iziko Museums of South Africa. He has expertise in identifying southern African bird bones, as well as larger mammals. With his little dog Suzy for company, we quickly got to work looking through my bird samples, using his impressive collection of reference bird skeletons. Each reference specimen has been carefully cleaned, each bone neatly labeled and placed into a brown cardboard box.

The trick is comparing a broken piece of mangled bone from the scat to a bone from the reference collection – which sometimes takes a while to find! Graham is remarkably good at this. If a bone is diagnostic, even if it’s just a fragment, we can narrow it down to a specific bird group and very often to a specific species. The best samples are those with a bit of coracoid, quadrate, furcula, tarsometatarsus or humerus.

Sometimes the sample resembles “rice crispies” (as Graham puts it), but quite often there was something identifiable. Often, we just have to use what we can get… Claws can be quite informative:

Sometimes there’s evidence of the caracal feeding on the bones:

And sometimes we have to look at a few different pieces. This gets tricky when there’s more than one species in the sample.

In the beginning we had a nice variety of birds: Cape francolin, Egyptian goose, guinea fowl, yellow billed duck and a gull here and there. However, as we started getting to the Cape Point area samples, things got a little less varied and a lot more predictable very fast. Things is, the caracals only really eat cormorants down there. Which would have been fine, except that all those samples were grouped together. So we had to look at 88 cape cormorant samples. Consecutively.

Fortunately, things have become a bit more interesting now that we’ve moved onto what I labeled as “unknown” and the larger mammals. We’re still working on those, and I’m really loving finally getting some confirmed identifications! It’s such a relief after staring at these samples for so long. The next step is to meet with Graham’s wife Margaret Avery who is the go-to expert on southern African micro-mammal cranial bones and teeth. I know most of the samples will be vlei rat, but I’m super interested to see which other species of rodents we’re going to find.

Two charismatic caracals' favourite snacks

First, to introduce the main cat characters. Protea is one of the adult female caracals and the 24th cat to be captured on the project. Her territory stretches along the white, sandy beaches on the wild, west coast from the Cape of Good Hope lighthouse through to Kommetjie, which she uses as a highway to travel from one hunting spot to the next. The UCP intern team have been following her movements closely, as she is one of the few females collared, as well as one of the few cats collared in the southern part of the Cape Peninsula. Titan is another interesting southern Peninsula character. As his name suggests, he's the biggest caracal captured, weighing in at 16kg (more than double Protea's mass!), and traveling pretty impressive distances usually on the eastern coast from Simon's Town down to around Dias beach.

Through ongoing effort scat and prey remains have been found at GPS clusters, and prey items identified, and these lend important data for the caracal diet analysis. Indeed, the data on these two cats have revealed some interesting results on what they like to eat, but most importantly that they don't seem to be very fussy eaters! Some of the most common prey items are Egyptian geese; these are Protea's favourite by far!  Other frequent items on her menu are sacred ibis, various gull species, and cape and white-breasted cormorants. Cape cormorants are a common breeding resident near Cape Point, but are an endemic species that is classified as endangered due to recent rapid declines.

Protea's feeding site remains include a few large spotted genets and grysbok, and the scat analysis so far shows she likes cape grey mongoose, and the occasional domestic cat.

The rest of her prey items are an assortment of birds: little egret, yellow-billed duck and cape francolin come up fairly regularly.

Of course, it's always exciting when unexpected prey items are found. Two notable species that became lunch are a rock kestrel, a species known to breed around the Cape Point area, and a sandwich tern, which is especially common along the coast in summer. Protea continues her finer taste for endangered birds in her partiality for African penguin. These seabirds are sometimes recorded off the west coast, presumably commuting to the nearby breeding colony at Boulders Beach in Simon's Town on the eastern side, which must be when she is able to catch them.

The value of scat analysis is that it reveals the small prey items often overlooked in other methods, probably because they are eaten whole! The scat analysis tells us that Protea likes to snack on smaller prey too... shrews and vlei rats feature often, and sometimes snake scales are also found.

Titan's diet is pretty similar, but a little less varied. He loves cape cormorant, and has certainly eaten a lot of them! The scat confirms this penchant for cormorant and also reveals that he occasionally goes for a rock hyrax (a.k.a. dassie), doesn't turn his nose up at vlei rats, striped mice and shrews, and also likes the salty taste of African penguin. One of the most amazing findings in Titan's scat were distinctive black and white quills! Yes, he's fierce enough to take on a crested porcupine.

A few more caracal lunches, and some mystery claws!

Ongoing student protests at UCT have really slowed things down, as many of my student volunteers have been unable to come to campus. It has been a very tumultuous time, with anxiety levels high. As a result I have not managed to process many samples. Nevertheless, there have been a few interesting ones!

One of the most intriguing samples was this one:

Mystery sample

Mystery sample

The fluffy grey hair looked rodent-like, but the bones were fairly robust, with a large vertebra. The strangest part was the huge claws! They couldn’t be from a cat, as they weren’t hooked enough, they were too large to be from a squirrel, rat, genet or mongoose, and they didn’t quite look like bird claws. I was at a loss…

After asking around and getting a few different suggestions for what this mystery prey item might be, I got a final say from Woody Cotterill, who has an interest and expertise in small mammals. Woody came to the lab to take a look at some of my samples and give some advice on how to go about identifying prey items.

Taking one look at the sample in the petri dish he said “It’s definitely Bathyergus.” Some quick Googling revealed that the prey item was most likely a Cape dune mole rat. This species is not only endemic to South Africa (i.e. its found only here), but its also the biggest of all the mole rats! I managed to get my hands on a taxidermic specimen, and was very surprised by how large it was. Roughly chihuahua-sized! But with much more impressive claws.

Now that I’m focusing more on prey identification, the detective work of the project has begun. My focus at the moment is to pull together a reference library to help me find out what these caracals are eating – not just from the scat but also from the kill remains found in the field. This involves looking at hair under a microscope, so I’m collecting hair from all potential prey items. I’ll also be using teeth and claws, as well as feathers for the birds. While the majority of samples will be the usual favourites on the menu, I’m sure there’ll be a whole lot more mysteries to solve.

Appreciation post

This project has challenged me in many ways so far, not least because I took it on so late in the year. I feel under constant time pressure with so much to catch up on and get done. Thankfully, I have a team of wonderful student volunteers who are passionate about carnivore biology and conservation! They have helped so much with processing my samples in their breaks between lectures and practicals, fitting it all into their busy schedules. So thanks guys!

The people who have helped me out so far are: Alveena Aziz, Caton Schutte, Clara Steyn, Dayna Hegarty, Kaelin Stemmet, Katherine Chaplin, Kyra McKellar, Lindsay Powell, Megan Pockalny, Michelle Pretorius, Shakirah Rylan, Tara van Ryneveld and Vivienne Coetzee. Thanks also go to some of the UCP interns who have become involved.

Gabi Leighton

SAWMA symposium 2016

I was fortunate enough to attend the annual South African Wildlife Management Association symposium in Tzaneen, Limpopo last month.

I presented some of the preliminary findings on the Cape Town caracals’ diet, focusing on the differences between two methods (kills found at GPS clusters and scat). We had to make a poster and also give a 5 minute speed-presentation of our work.

This was a really valuable few days of interesting talks and people. Very glad that I went and was super pleased to win the prize for the best student poster!

Preview of the poster I presented at the symposium

Preview of the poster I presented at the symposium

I think the next symposium will be in the Western Cape, so hopefully I can go again, and this time do a longer talk about my work!

Gabi Leighton

Some (very) preliminary diet findings

Here are a few of the more interesting prey items found in the scat analysis so far. Most of the samples contain mammalian prey items (i.e. composed mainly of hair), and of those, most seem to be rodent. I still need to go through all those with hair and look at cross-sections under the microscope to identify the species (or at least to genus level). Nevertheless, these are the more exciting ones:

Hope you enjoy the photos!

Gabi Leighton

Caracal diet field trips

I was lucky enough to join in on some field work action earlier this year… This involves setting traps to catch the cats (much trickier than it sounds!) and investigating GPS clusters (i.e. points where the cats have been hanging out for a while) to find evidence of kills and scat, which I’m using for my diet analysis.

No such thing as a free caracal lunch

This is just a brief introduction to the caracal diet aspect of the Urban Caracal Project, which will also be documented here.

I’m an MSc Biological Sciences student in my first year of study at the University of Cape Town. My research aim is to investigate the diet of caracal (aka “rooikat”) living and hunting in the urban spaces of Cape Town, South Africa. These elusive yet adaptable medium-sized cats have managed to persist in a city with an increasingly hardening urban edge; using greenbelts, empty land as well as natural areas. The latter is mostly land forming part of the Table Mountain National Park (TMNP).

Most citizens of Cape Town are surprised to hear that caracals live in such close proximity, perhaps illustrating how good they are at going unseen! As can be seen on this website, a lot of really exciting work is being done to study the effects that urbanisation is having on these cats, from movement patterns and gene flow to rodenticide and disease exposure. My project is a small part of this larger ongoing research effort and will investigate their diet. However, I’m hoping to make it a bit more interesting for myself by putting the dietary data in a spatial context, linking what they choose to eat, where they choose to eat it and how this is influenced by urbanisation. We expect that while there might be easy pickings near the urban edge, this may draw caracals closer to the risks of the big city… There ain’t no such thing as a free lunch!

Gabi Leighton