Spotlight on Zoo Science
May 26,
2003
Fishing Cats Enjoy City Life
Fishing cats (Prionailurus virverrinus) are a flagship species for a suburban nature reserve in Colombo, the capital of the Asian island nation of Sri Lanka.
 Fishing cats can live in suburban and urban environments. |
A fishing cat was recently reported seen crossing the main road leading to the Parliament. The news appeared on a local naturalist’s listserv, which catalyzed several others to send in their own observations. This was remarkable because the observations were from residential areas in Colombo, the largest city in Sri Lanka. |
When we think of threatened or endangered larger mammals, we usually think of wilderness. We believe we have to go to the last wild places to find and study them. But could it be that this little known cat is living right under our nose in suburban—even urban—Asian environments? Can we conserve them in the remnant habitats that have survived urban sprawl?
Called that “bull dog” of cats by one biologist, the fishing cat is the largest of the lineage of south and southeast Asian wild cats that includes the leopard cat (Prionailurus bengalensis), flat-headed cat (P. planiceps), and the closely related rusty-spotted cat (P. rubiginosus), which is arguably the smallest of the wild cat species.
A powerful, deep-chested animal, with shorter legs relative to those of other cats of the same size, males can weigh up to 12 kilograms (26 pounds) but females are markedly smaller—which makes them about the size of an ocelot or Canadian lynx. The fishing cat’s luxurious spotted pelt was much sought after in the fur trade. Today, the principle threat to their survival is degradation and loss of their habitat.
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Fishing cat habitat in Colombo, Sri Lanka |
Fishing cats live in the thick vegetation associated with watercourses, wetlands, and mangrove forests, which are also areas that people prefer to clear and live in. As their name implies, they eat fish but also frogs and waterfowl that live at the interface of the terrestrial and aquatic ecosystems.
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A fishing cat dives
head-first to catch a fish underwater. |
They scoop fish out of the water with their paws, much as a house cat does from a back yard pool, but quite unlike house cats, they also jump in head-first to capture their aquatic prey. Fishing cats have been reported to take swimming ducks by coming up from underwater to capture them.
When there is opportunity, they eat poultry, which, unfortunately, leads them into conflict with people. They also will eat from a dead carcass, such as those thrown into the water for disposal, and this makes them vulnerable to poisoning.
The wetlands, mangroves, and riparian habitats this cat needs to survive are under immense pressures from people and are undergoing massive conversions in south and southeast Asia, as they are nearly everywhere. Yet, these sensitive habitats are vitally important to regional economies, offering ecosystem services ranging from protecting water quality and mitigating floods and drought, to providing protection from tropical storms.
One prime fishing cat habitat, the great mangrove forest at the mouths of the Ganges, known as the Sundarbans, is a major nursery for the fisheries in the Bay of Bengal that provide food for enormous numbers of people.
Therefore, fishing cats are what we call an indicator species; their presence may indicate the ecosystem is operating at a high level of quality and best achievable ecosystem function.
The distribution of fishing cats has been plotted over the last century and biologists know that this species occurs in several separate populations with no recent possible connections between them. However, they may have been connected during the Pleistocene, when sea levels were as much as 85 meters (280 feet) lower than they are today.
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Fishing cats have an unusual disjunct
distribution. |
Today, fishing cats occur on the Indonesian islands of Sumatra and Java, which are now separated by the Sunda Straits, which once formed a land bridge between the two islands. It is a puzzle that they do not occur in Borneo, which also was formerly connected to Sumatra and Java. Equally puzzling, they are also absent in Peninsular Malaysia even though they occur again in neighboring Thailand.
The range extends through the rest of Southeast Asia and into the Indian subcontinent, where they are restricted to the western extent of the forest and tall grasslands that skirt the base of the Himalayas in Nepal and northern India. A few isolated populations are known from well-watered habitats nested in tropical dry forest in northern India, south of the Ganges River.
They occur in the Sundarbans of Bangladesh and India but not along the coast of the Indian subcontinent, except on the southwest Kerala coast. A relic population lives, or did until recently, on the Indus River Delta in southern Pakistan. And they live on the island of Sri Lanka.
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Our study asks, how
can fishing cats persist in an urban wetland in Sri Lanka? |
The fishing cats in the lower Indus River Delta and the Kerala coast populations have probably been extirpated. This made the observation of a fishing cat crossing a main road in Colombo all the more interesting. Given what we know about fishing cats, their distribution, and their ecological needs, what is going on in Colombo that enables fishing cats to persist in this urban setting?
To find out, I talked with Dr. Eric Wikramanayake, a senior scientist with the WWF-US Conservation Science Program. Eric is a former Smithsonian Institution Post-doctoral Fellow, now a Research Associate with the National Zoo, and is based in Colombo. His work has embraced such wide-ranging topics and places as Komodo dragons on Komodo Island in Indonesia, endemic freshwater fishes in Sri Lanka, and planning for tiger conservation core areas and connecting corridors in Nepal and Bhutan.
Eric agreed that we could learn something about these urban and suburban fishing cats by using interviews and camera traps. We needed an interviewer/camera trapper and he knew a promising young biologist, Suchitra Balagalle, who was looking for a project for her master’s degree at the Open University in Colombo. Dr. K. Padmala, her advisor, was fully supportive. We had our team. With a grant from Friend of the National Zoo, we had our project.
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The wetland sanctuary where fishing cats are being
studied. |
After spending some time asking around to find out who had seen fishing cats and where we might expect to find them, we settled on the Bellanwila-Attidya Sanctuary in the Weras Ganga-Attidiya area in south Colombo. This sanctuary, a 372-hectare (1.4 square-mile) patch of wetland with a rich fauna, surrounded by residential areas, It is a mere 100 meters (328 feet) from the Ratmalana Airport.
Over the years, the northern portion of the sanctuary had received management attention and people respected it as sanctuary. The southern half of the sanctuary had received much less attention and thus its status as a sanctuary was ignored. The sanctuary included a portion of an old canal-lake system built in the early colonial period by the Dutch. This was the key to fishing cat habitat.
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A camera trap ready to photograph a passing
animal. |
Following interviews and reconnaissance to look for suitable areas, we set out our camera traps all around the edges of the lake and along the edges of the old canal in both the managed and less-managed areas of the sanctuary, often less than 100 meters from residential areas. The fishing cats took their own pictures by breaking a sensory beam that triggers the camera shutter as they walked past.
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| This fishing cat seems unhappy about being "trapped." |
This study shed light on the behavior and ecology of this little-studied wild cat that, ironically, lives so close to human habitation. For instance, the time recorded on the photographs indicated that fishing cats are active both day and night. Although people reported seeing them very early in the morning, when they go out to tend their cattle and buffaloes, the photographs showed fishing cats walking around at mid-day.
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A fishing cat out and about during the day |
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A pair of fishing
cats captured by the camera trap at night |
When Suchitra examined fishing cat dung, she found that the cats had killed and eaten porcupines. So they evidently supplement aquatic prey with more terrestrial animals. But Suchitra and Eric also had a more challenging problem on their hands. Through interviews with local residents, Suchitra found that fishing cats are often accused of preying on chickens and ducks, which created a conflict.
So, Eric and Suchitra have begun an awareness campaign among the local residents and at local schools, to impress upon people that what they have in their backyards is something special—an endangered wild cat that needs to be conserved. They are also recommending other steps, such as keeping domestic poultry in enclosures, to mitigate the conflicts.
They are reassessing the sanctuary boundary so it will include essential fishing cat habitat while excluding residential areas that are now within the boundary. The fishing cat will be used as a flagship species to promote this objective and ensure that this sanctuary, a wetland area, will be well-managed.
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Painted storks in
the Colombo wetlands sanctuary where fishing cats live |
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Rusty-spotted cats
have not been seen. |
Conservation biologists are increasingly aware of how competition between carnivore species influences the distribution and abundance of the carnivores and their prey. Carnivores of different species may avoid each other if they come into visual or olfactory contact. Active avoidance between one or more species can result in shifts in habitat use for each species.
If the carnivores share common food resources, one species can reduce the amount available for the second. One species may routinely steal the kills of a second, a type of type of competition termed kleptoparasitism. And, finally, carnivores of one species do kill members of other species. Tigers kill leopards when they can catch them. In Nepal’s Royal Chitwan National Park I have see a leopard cat pursued and killed by a leopard. Zoo research associate Dr. Dave Smith, the only person to have radio tracked a fishing cat, told me the fishing cat he tracked in Chitwan always took a wide birth around forest patches where tigers and leopards lay up during the day and hunt at night.
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| Leopards may affect fishing cat behavior. |
We don’t know yet how conditions and competition between these carnivore species are shaping the suburban-living carnivore complex around Colombo, but aim to find out during the next phase of this exciting study.
In areas where the top carnivore is gone or conditions preclude its presence, the second predator down in size is frequently more abundant than if the top carnivore was present. This impacts through the food chain in what biologists call tropic cascades; basically, with the top carnivore absent, all the smaller carnivores are more abundant. This is called meso-carnivore release.
With an increase in smaller carnivore numbers we see a significant impact on their prey through increased predation rates. A comparison of fishing cat ecology and behavior in natural habitats through radio-tracking and camera-trapping will shed some light on these ecological relationships among Sri Lanka’s carnivore community.
As a next step, we will radio-track fishing cats to follow their movements. This will allow us to determine how close they come to residential areas at different times of the day, over what areas they range, and give us a better understanding of their behavior. We will then compare the behavior of fishing cats living in suburban and urban settings, with that of fishing cats living in more natural environments, far from human habitation, where larger wild cats such as the leopard lives.
But what about that fishing cat reported near the Parliament? We don’t know yet. Suchitra set up a camera trap at what she thought was a good crossing point. But these are sensitive times. Someone reported a strange-looking, camouflaged object chained to a tree. Because the site was close to the place that politicians gather to discuss state matters, the object was reported to the police, who called in the bomb squad. The camera was duly “defused” before Suchitra could retrieve it, so we can only wonder if it ever managed to capture the fishing cat on film. Such are the challenges facing a conservation biologist working to understand a threatened cat living in this most human-dominated of landscapes.
—John Seidensticker, Senior Scientist
This work is supported by a grant from Friends of the National Zoo.
Note to Media: If you would like more information about this project, or any of the Zoo's conservation and science programs, please contact the Zoo's Office of Public Affairs.
