Survival of some small wildcats at risk due to housecat hybrids

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  • Small wildcat species suffer from habitat loss, hunting and human conflicts, just like better-known big cats. But some small wildcat populations also face threats from other felines: hybridization.
  • Interbreeding with domestic cats (Felis catus), and also with other wildcat species, can alter the outward appearance, behaviors and genetic profiles of wildcats, and create conservation dilemmas about how best to define and protect a species.
  • In Scotland, hybridization caused the functional extinction of a subpopulation of European wildcat (Felis silvestris), but scientists and conservationists are collaborating to rebuild the genetically distinct wild population with kittens reared from selectively bred wildcats.
  • To protect the African wildcat (Felis lybica) in South Africa, international partners are working to reduce interbreeding by sterilizing domestic and feral cats near the borders of Kruger National Park. Hybridization can also occur between wildcat species and raises questions about preserving genetic purity vs. ecosystem function.

Charismatic big cats (think tigers and leopards) get the lion’s share of conservation attention, while their close relatives — 33 species of small wildcats roaming five continents — get far less notice. Yet they too often urgently need protection.

Like their larger counterparts, these felids suffer from habitat loss, hunting and human conflicts. But some face a less-known feline threat: hybridization with Felis catus, the domestic cat — darling to cat lovers the world over and YouTube superstars.

In Europe and South Africa, interbreeding by small wildcats with housecats or feral domestic cats has altered the genetic makeup of wild species and created conservation dilemmas.

To preserve the genetic integrity of these wildcats, conservationists plan to boost dwindling populations with wild-bred kittens, ramp up sterilization of feral domestic cats, and find better ways to study these elusive wild felids.

Doing so is important not only for individual species, but for protecting ecosystems from instability. “Small wildcats are habitat specialists and their losses can have wide impacts,” says Wai-Ming Wong, director of NGO Panthera’s small cats program. “Given the current biodiversity crisis, it’s really important to maintain ecosystem balance.”

Hybrids have always posed a conundrum for conservationists. Admixing “domestic” genes with the DNA of wild species through crossbreeding — a process known as introgression — can increase genetic diversity and even improve a species’ ability to prevail in a changing landscape. But the distinct genetic heritage of wild species can be lost via intermating.

Wild-domestic hybrid cats, for example, may display different behaviors from those in the wild, alter their use of habitat, or be more susceptible to disease. These crossbred cats also might not meet the specific genetic and taxonomic criteria that form the basis of legal protections for wildcats.

A Highland tiger.
The Highland tiger, a subpopulation of the European wildcat (Felis silvestris) found in Scotland, was declared functionally extinct in a conservation status assessment published in 2019. Scientists hope to restore it, if possible. Image courtesy of RZSS/Saving Wildcats.

Holding onto Scotland’s Highland tiger (Felis sylvestris)

“Hybridization is a tricky issue,” says Helen Senn, head of conservation at the Royal Zoological Society of Scotland (RZSS) in Edinburgh and project lead for Saving Wildcats, an NGO. That’s especially the case for a subpopulation of European wildcat (Felis sylvestris) that once roamed Scotland, but which has been hit hard by wild-domestic hybridization.

Today, studies show that few of Scotland’s remaining wildcats (outside of zoos) display enough of the distinct genetic markers and physical traits to be defined as the “Highland tiger.” Although domestic cats were likely introduced to the United Kingdom in Roman times, whole genome studies point toward hybridization as “a recent phenomenon that probably only happened within the last 60 or so years,” Senn says.

That’s an important point for conservationists because “that tells us something changed to create a breakdown between these two species,” she explains. As habitat loss and persecution of Scotland’s wildcats escalated in recent decades, the dwindling population of Felis sylvestris likely mated with the more available domestic cat, Felis catus.

“Then things rapidly descended into what we call a ‘hybrid swarm,’” says Senn. “Which just means that everything is very mixed up [genetically].” In other European countries, analyses find that interbreeding with domestic felines affects anywhere from 3-21% of wildcat populations. But in Scotland, all of the wild-living cats in study samples show evidence of hybridization.

Map showing the complexity of wildcat hybridization across Europe.
Map showing the complexity of wildcat hybridization across Europe. Blue dots are purebred wildcats (WC); Orange triangles are first-generation hybrids (F1); Yellow stars are second-generation hybrids (F2); Light blue squares are backcrosses to wildcats (BxWC); Pink squares are backcrosses to domestic cats(BxDC); Light gray grid cells represent the known distribution of wildcats; Pure domestic cats (n = 187) and samples uncategorized (n = 8) are not displayed. Image by Tiesmeyer et al., 2020 (CC BY 4.0).

Today, Senn leads a European partnership tasked with rebuilding Scotland’s wildcat population. The collaborators plan to reintroduce wildcats into remote areas where the organization can still monitor the more isolated cats’ welfare.

Over the next three years, conservationists plan on annually releasing about 20 kittens from breeding pairs of captive (zoo) and wild-caught felines that scored at least 75% on a combination of specific wildcat genetic markers and pelage characteristics.

“The genetics are very important to helping us resolve taxonomy and understand what we’re trying to conserve,” said Senn, a conservation genetics specialist whose work ranges from the reintroduction of pond mud snails in Scotland to the scimitar-horned oryx in Chad.

Scottish wildcat juxtaposed w/domestic brown tabby
Wild or not? The standard for deciding what now defines a wildcat combines a pelage scoring test and a genetic test based on 35 specific markers. The genetics scores are given a higher weighting than pelage for selecting breeding cats for conservation in Scotland. The seven pelage characters are: (1) extent of dorsal stripe, (2) shape of tail tip, (3) distinctness of tail bands, (4) presence/absence of broken stripes and (5) spots on flanks and hindquarters, (6) shape and number of stripes on nape and (7) on the shoulders. “I wish we were Star Trek, but we’re not. We are still far from instantaneous genetic testing in the field. In the field we use the pelage test,” explained Helen Senn, a RZSS conservation genetics specialist. Images courtesy of (left) RZSS/Saving Wildcats and (right) Mark Oppenheim.

Earlier this year, the first cohort of young wildcat kittens were old enough to move into individual enclosures at the Highland Wildlife Park, where they can continue to mature and work on their survival skills. They should be ready to release by the middle of the year.

After release, the young cats will be tracked using GPS collars and camera traps. Senn also wants to monitor the genetics of subsequent generations through fecal samples, hair traps and camera images. The scientist will also be comparing the DNA profiles of the wildcats with samples from the feral domestic felines that roam the same general area.

Studies on the rebound of the European wildcats in the Swiss Alps have modeled the size of wildcat populations needed to preserve the species’ genetic legacy, but Senn doesn’t  know exactly how many cats need to be reintroduced to keep the Scottish wildcat from being overwhelmed by domestic cat DNA.

“We want to see a population of wildcats which are basically fit, with healthy numbers, that are reproducing with each other, and not breeding with domestic cats,” she says. “If we can do that, then we are onto a winner.”

Scottish Highland wildcat kittens
Scottish Highland wildcat kittens exploring the enclosure in which they’re being raised. When ready, these small cats will be released into the wild. Image courtesy of RZSS/Saving Wildcats.
An African wildcat
An African wildcat at the Satara Camp in Kruger National Park. A purebred African wildcat typically has long front legs, an orange tint to the ears and no white spots. Also typically, African wildcats are elusive and rarely seen, but this one seemed more used to people. Image by Bernard Dupont via Flickr (CC BY-SA 2.0).

Saving the African wildcat in South Africa

Hybridization is also a concern in South Africa, where the dust-colored, long-legged African wildcat (Felis lybica) roams. Although a 2016 IUCN survey found that F. lybica interbreeding with domestic cats has been fairly low across Africa’s broader landscape, the threat to the wildcat tends to be highest in parts of South Africa where human populations (and domestic cat numbers) are highest — especially near the borders of national parks.

One key recommendation coming out of the IUCN survey is to actively neuter domestic cats in these border areas to create buffer zones that reduce crossbreeding, says Louise Holton, president of Alley Cat Rescue (ACR), a U.S.-based nonprofit. Local veterinarians were already taking this approach, but ACR funding has helped ramp up trap-neuter-return (TNR) capacity around Kruger National Park. This approach takes care to return sterilized cats to the areas where they were found so that established cat populations are maintained, and there’s no “vacancy” created for an influx of new cats.

feral domestic cats
The trap-neuter-return (TNR) program is a key element in the Alley Cat Rescue action plan, says ACR president Louise Holton. The ACR funds and collaborates with partner organizations that do the physical trapping of feral domestic cats, transport them to vet clinics, and release them. Image courtesy of Louise Holton/Alley Cat Rescue.

“The [feral cat] problem is enormous and ACR was able to help [veterinarians] scale up,” says Holton, who is originally from South Africa.

More than 5,000 feral and stray domestic cats have been sterilized and vaccinated against rabies since 2019, at a cost of around $45 per cat. The project has expanded its capacity to include three additional organizations, but Holton estimates there are still at least 3,500 unneutered cats around Kruger National Park, and thousands more near other parks. She especially wants to get blood samples for genetic analysis from hybrid-looking cats undergoing sterilization to get more DNA data on hybridization.

In 2021, the ACR started an African Wildcat Project to map the distribution of the population based on firsthand reports and photos of wildcat sightings submitted through the project’s Facebook page.

AWC pure vs hybrid cats.
Sorting out the pure wildcats from the hybrids by looks alone can be tricky. According to experts, the cat on the right appears to be a hybrid. The left image is a wildcat found orphaned near Kruger National Park and brought to the Moholoholo Wildlife Rehabilitation Centre. Workers there named him Dumpling. When ACR heard about him, they paid for genetic testing, which showed Dumpling to be a pure African wildcat. However, he hasn’t been released and is still at the centre, because he hasn’t shown enough skill to survive on his own so far. He also seems overly comfortable with people, which could also be dangerous for the wildcat if he were released. Images courtesy of Louise Holton/Alley Cat Rescue.

Holton notes that African wildcats and brown domestic tabbies share some similarities, but the wildcats have long front legs and an orange tinge to the ears, while hybrids have lost the long front legs and always have white spots somewhere — small but important visual distinctions when trying to identify and maintain the integrity of a wild species.

In addition to fieldwork, Holton is working rigorously to obtain more funding to keep these projects going. “African wildcats are amazing creatures,” she says. “And that’s where our beloved domestic cats started 10,000 years ago. Why not use a sterilization program that will stop the hybridization, yet keep the [wildcat] population doing what they should do?”

(Left) Geoffroy’s wildcat. (Top-right) Southern tiger wildcat. (Bottom-right) Geoffroy’s tiger-cat hybrid
These cat images were captured by camera traps in Rio Grande do Sul state, Brazil, near the Uruguay border. Left, a Geoffroy’s wildcat. Top right, a Southern tiger wildcat. And bottom right, what researcher Jim Sanderson calls a Geoffroy’s tiger-cat hybrid, a cross between Leopardus geoffroy and Leopardus guttulus. Images courtesy of Jim Sanderson/Lynn Culver.
The hybrid zone map.
The hybrid zone where at least 40% of the individuals sampled in Brazil’s Rio Grande do Sul state were identified as crossbred wildcats.  The red circles are pure L. guttulus; blue circles are pure L. geoffroyi, and the green circles represent hybrids. The background colors on the map correspond to the two biomes found in the state: Atlantic Forest (green) and Pampa (tan). The area delimited by the thick lines correspond to a central region spanning about 160 kilometers (100 miles) in a north-south direction, where the highest concentration of genetically identified hybrids was observed. The dashed black line at the center of the map corresponds to the geographic limit between the distributions of the two cat species. Image courtesy of Trigo et al., 2014 (CC BY 4.0).

Reducing human-wildcat conflicts

Domestic cats aren’t the only threat to the pure genetic lineages of various small wildcat species. In southern Brazil, for example, researchers found at least 40% hybridization between two wild species, Geoffroy’s cat (Leopardus geoffroyi) and the southern tiger cat (Leopardus guttulus), when they analyzed DNA samples in Rio Grande do Sul state.

The main “hybrid zone” was at the southern extent of the much-fragmented, very ecologically stressed Atlantic Forest and the northern extent of pampas grassland where the two wildcats’ ranges overlap.

The hybrids aren’t easy to distinguish by looks alone: purebred Geoffroy’s cats are generally more robust and spotted with non-remarkable tails; southern tiger cats are typically lithe with long tails, stripes or open spots, and larger ears.

Researcher Jim Sanderson with a güiña during his trap/track doctoral studies.
Researcher Jim Sanderson with a güiña wildcat during his trap/track doctoral studies. Image courtesy of Jim Sanderson.

But looks aren’t the key issue, says Jim Sanderson, founder and director of the nonprofit Small Wild Cat Conservation Foundation (SWCCF) and an IUCN small cat specialist.  “I think it’s more important to [maintain a specific] ecological role in nature than to be fixated on hybrid [looks],” Sanderson says. “Functional extinction is a terrible loss. So I’d rather have a weird-looking cat than no cat at all.”

In the increasingly human-dominated landscapes where he works, Sanderson focuses on finding ways to mitigate the conflicts with people that get wildcats killed. In Chile, for example, the diminutive güiña (Leopardus guigna) often preys on chickens raised by local farmers. The Pampas cat (Leopardus colocolo) has a similar penchant.

Fewer felines suffer from retaliatory killings when henhouses are repaired and cat-fortified, or when people are supplied with tailless chickens that are harder for wildcats to catch.

Other practical conservation approaches include equipping rural herders with guard dogs to stop wildcat-associated predation of alpacas, llamas and goats. Protecting bigger cats, such as mountain lions, can also help the small cats because the big cats can reduce populations of feral dogs that threaten smaller felids. “I just want to keep cats in the game,” says Sanderson.

Wai-Ming Wong, Panthera’s small cat program director.
“Scientists are somewhat addicted to camera traps,” says Wai-Ming Wong, Panthera’s small cat program director. “They are your eyes in the forest. But what you can do for big cats — set them high up from the ground, leave them at 2-3 kilometers apart — doesn’t always work for getting small wildcat data.” Image courtesy of Panthera.

Small wildcat future

A major hurdle to understanding the impacts of hybrids on the ecological roles played by small wildcats is the lack of studies to determine what these species need to thrive. That’s  partly because small cats are incredibly elusive, with many conservationists having rarely — if ever — seen the cats they’re trying to save. And also because research into the 33 species of small wildcats isn’t funded at anywhere near the levels of their big cat relatives.

“We have thousands of detections of tigers on camera traps, even though they are a critically endangered species,” notes Wai-Ming Wong of Panthera. “But we have maybe 15 or 20 of the clouded leopard [Neofelis nebulosa] which occupies the same habitat.” With so few detections, the usual statistical analyses can’t be applied to these smaller species, explains Wong.

One solution for building knowledge of small cat species is the collection of environmental DNA samples from soils or waterbodies. To get population baselines — and detect hybridization — scientists need to analyze genetic materials at the species and individual level, and compare genetic relatedness.

“Genetics will be a key method for us to be able to understand the wildcats’ ecology,” Wong says. Without this fundamental data, it’s hard to accurately assess threats to these species and make conservation management plans.

Although big cats have long captured the public’s imagination, Wong thinks small wildcats are charismatic and capable of capturing people’s hearts. At his conservation talks, every time people see pictures of Asia’s Pallas’s cat (Otocolobus manul) — dubbed “the original grumpy cat” — he says they’re immediately captivated and want to know all about it.

With their mid-level trophic role in ecosystems, acting as both predator and prey, small wildcats are important sentinels for detecting ecosystem degradation. They can also be vital for rodent and small mammal control (critical to balanced ecosystems and to helping farmers protect crops at no cost). Perhaps, with some creative public relations work, small wildcats could become ambassadors for threatened habitats the world over.

Wong sees hybridization as an emerging threat to small cat species — occurring naturally in some populations and catalyzed by humans in others. One thing that’s clear, says Wong, is that each small wildcat species has its own unique set of challenges. “That means there’s no one-size-fits-all approach to their conservation,” he says.

Banner image: A domestic cat out in the wild. Image by Cloudtail the Snow Leopard via Flickr (CC BY-NC-ND 2.0).

Small cats face big threats: Reasons to save these elusive endangered species

Citations:

Breitenmoser, U., Lanz, T., & Breitenmoser-Würsten, C. (2019). Conservation of the wildcat (Felis silvestris) in Scotland: Review of the conservation status and assessment of conservation activities. IUCN SSC Cat Specialist Group, Bern, Switzerland. Retrieved from https://iwbond.org/wp-content/uploads/2021/12/Wildcat-in-Scotland-Review-of-conservation-status-and-activities_1.pdf

Herbst, M., Foxcroft, L., Le Roux, J., Bloomer, P., & Do Linh San, E. (2016). A conservation assessment of Felis silvestris. In Child, M.F., Roxburgh, L., Do Linh San, E., Raimondo, D., & Davies-Mostert, H. T. (Ed.). The Red List of Mammals of South Africa, Swaziland and Lesotho. South African National Biodiversity Institute and Endangered Wildlife Trust, South Africa.

Howard-McCombe, J., Ward, D., Kitchener, A. C., Lawson, D., Senn, H. V., & Beaumont, M. (2021). On the use of genome-wide data to model and date the time of anthropogenic hybridisation: An example from the Scottish wildcat. Molecular Ecology, 30(15), 3688-3702. doi:10.1111/mec.16000

Kitchener, A., Yamaguchi, N., Ward, J., & Macdonald, D. (2005). A diagnosis for the Scottish wildcat (Felis silvestris): A tool for conservation action for a critically-endangered felid. Animal Conservation Forum, 8(3), 223-237. doi:10.1017/S1367943005002301

Quilodrán, C. S., Nussberger, B., Macdonald, D. W., Montoya-Burgos, J. I., & Currat, M. (2020). Projecting introgression from domestic cats into European wildcats in the Swiss Jura. Evolutionary Applications, 13(8), 2101-2112. doi:10.1111/eva.12968

Senn, H. V., Ghazali, M., Kaden, J., Barclay, D., Harrower, B., Campbell, R. D., … Kitchener, A. C. (2018). Distinguishing the victim from the threat: SNP-based methods reveal the extent of introgressive hybridization between wildcats and domestic cats in Scotland and inform future in situ and ex situ management options for species restoration. Evolutionary Applications12(3), 399-414. doi:10.1111/eva.12720

Tiesmeyer, A., Ramos, L., Manuel Lucas, J., Steyer, K., Alves, P. C., Astaras, C., … Nowak, C. (2020). Range-wide patterns of human-mediated hybridisation in European wildcats. Conservation Genetics, 21, 247-260. doi:10.1007/s10592-019-01247-4

Trigo, T. C., Tirelli, F. P., de Freitas, T. R. O., & Eizirik, E. (2014). Comparative assessment of genetic and morphological variation at an extensive hybrid zone between two wild cats in Southern Brazil. PLOS ONE, 9(9), e108469. doi:10.1371/journal.pone.0108469

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