Modelling biological control of cat populations

Courchamp, F. & G. Sugihara. 1999. Modelling biological control of alien predator populations to protect native island prey species from extinction. Ecological Applications, 9: 112-123.

Introduced feral cat (Felis catus) populations are an important threat to many island vertebrate populations and to bird species in particular. Elimination of feral cat populations is desirable in most of these ecosystems. Release of a parasite species in these mostly immune-naive populations is thought to be an efficient eradication measure. Such an approach is theoretically investigated here, using a mathematical model that describes the effects of introducing a virus into the cat population on population dynamics of both the cat and its prey. We studied the effects of two types of introduced feline viruses: Feline Immunodeficiency Virus and Feline Leukemia Virus, both of which are good candidates for eradicating a cat population. Results show that eradication is possible with Feline Leukemia Virus, if natural immunity is sufficiently low. Feline Immunodeficiency Virus cannot fully eradicate cat populations, but can be an effective agent for long-term control of cat populations on islands where total cat eradication is not possible (e.g., there is a high likelihood of continued introduction of cats) or not desirable (e.g., when rats are present). Culling, which by itself would require a very prolonged and logistically demanding effort to eliminate cat populations, may be more efficient when applied simultaneously with virus introduction.

Mammals invaders on islands

Courchamp, F., J.-L. Chapuis & M. Pascal. 2003. Mammal invaders on islands: Impact, control and control impact. Biological Reviews, 78 (3): 347-383.

The invasion of ecosystems by exotic species is currently viewed as one of the most important sources of biodiversity loss. The largest part of this loss occurs on islands, where indigenous species have often evolved in the absence of strong competition, herbivory, parasitism or predation. As a result, introduced species thrive in those optimal insular ecosystems affecting their plant food, competitors or animal prey. As islands are characterised by a high rate of endemism, the impacted populations often correspond to local subspecies or even unique species. One of the most important taxa concerning biological invasions on islands is mammals. A small number of mammal species is responsible for most of the damage to invaded insular ecosystems: rats, cats, goats, rabbits, pigs and a few others. The effect of alien invasive species may be simple or very complex, especially since a large array of invasive species, mammals and others, can be present simultaneously and interact among themselves as well as with the indigenous species. In most cases, introduced species generally have a strong impact and they often are responsible for the impoverishment of the local flora and fauna. The best response to these effects is almost always to control the alien population, either by regularly reducing their numbers, or better still, by eradicating the population as a whole from the island. Several types of methods are currently used: physical (trapping, shooting), chemical (poisoning) and biological (e.g. directed use of diseases). Each has its own set of advantages and disadvantages, depending on the mammal species targeted. The best strategy is almost always to combine several methods. Whatever the strategy used, its long-term success is critically dependent on solid support from several different areas, including financial support, staff commitment, and public support, to name only a few. In many cases, the elimination of the alien invasive species is followed by a rapid and often spectacular recovery of the impacted local populations. However, in other cases, the removal of the alien is not sufficient for the damaged ecosystem to revert to its former state, and complementary actions, such as species re-introduction, are required. A third situation may be widespread: the sudden removal of the alien species may generate a further disequilibrium, resulting in further or greater damage to the ecosystem. Given the numerous and complex population interactions among island species, it is difficult to predict the outcome of the removal of key species, such as a top predator. This justifies careful pre-control study and preparation prior to initiating the eradication of an alien species, in order to avoid an ecological catastrophe. In addition, long-term monitoring of the post-eradication ecosystem is crucial to assess success and prevent reinvasion.

FIV epidemiology in rural cats

Courchamp, F., N. Yoccoz, M. Artois & D. Pontier. 1998. At-risk individuals in Feline Immunodeficiency Virus epidemiology: evidence from a multivariate approach in a natural population of domestic cats (Felis catus). Epidemiology and Infection. 121: 227-236.

Prevalence of Feline Immunodeficiency Virus (FIV) infection was measured during 6 consecutive years in a natural rural population of domestic cats. Sex, age, weight, origin, group size and presence of antibodies to FIV were recorded for each sampled cat. Logistic regressions were used to estimate the influence of the recorded parameters on infection. FIV prevalence rates are as high as 19.6% in the total population, and do not statistically change between years, after controlling for changes in samples' age structure. FIV infection is characterized by risk factors linked to aggressive behaviour: old mature male adults having dispersed are more likely to be infected. A study of the cats group size and of the spatial distribution of infected individuals indicates the absence of infection clusters in males, and suggests the importance of roaming in the spreading of FIV. In conclusion, FIV infection spreads, with low contagiousness, mainly between particularly aggressive individuals, and the virus is endemic in this population.

Impact of two feline retroviruses on natural populations of domestic cat

Courchamp, F., D. Pontier, E. Fromont & M. Artois. 1995. Impact of two feline retroviruses on natural populations of domestic cat. Mammalia. 59 (4): 589-598.

We compared the pattern of spread and the impact of two retroviruses, feline immunodeficiency
virus (FIV), and feline leukemia (FeLV) within natural populations of domestic. A four years epidemiological study shows that FIV is present in three studied rural cat populations, whereas FeLV is absent in one out of the three, with no evolution in time for either virus. Factros influencing FIV transmission are directly linked to agressive behaviour , while factors influencing FeLV transmission are rather characteristic of amicable interactions. Results of a deterministic model show that both infections are maintained in the population at a stable equilibrium between susceptible and infected animals, slightly reduce the number of individuals at equilibrium, and have long transmission rates. Results of a long term dynamical study indicate that the probability of dying from tese viruses is low in natural conditions, and that, despite their presence, the size and structure of the population remains stable.
In conclusion, despite FIV and FeLV have different spread patterns (FIV infects and kills at-risk individuals, while FeLV infects more indiscriminately), the impact of both retroviruses on cat populations seems to be low. 

Infection strategies of retroviruses to control feral cats

Fromont, E., Courchamp, F., Pontier, D., & Artois, M. (1997). Infection strategies of retroviruses and social grouping of domestic cats. Canadian journal of zoology, 75(12), 1994-2002.

It is thought that parasites may exert selective pressure on the social structure of host populations. We compared the impact of feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV), two retroviruses commonly found in domestic cats (Felis catus). Because of low transmissibility and virulence, both infections have a worldwide distribution and low prevalence. Transmission modes differ: FIV is transmitted only through biting, while FeLV transmission occurs by biting, licking, grooming, and sharing food and from mother to fetus. FeLV is also more pathogenic than FIV. We compared FIV and FeLV prevalence and risk factors within five populations of cats. FIV infection occurred almost exclusively among adult male cats fighting to acquire and maintain dominant status. Classes at risk for FeLV infection included sexually intact cats allowed to roam freely. The impact of FeLV on host population growth was greater than that of FIV but varied among populations. Our results show that FIV is favoured by individual aggressiveness and a hierarchical social system, while FeLV is more prevalent among socially active cats. FeLV may constitute a source of selective pressure against numerous amicable contacts, particularly in urban cat populations, where aggression among individuals is reduced.

Modelling FIV

Courchamp,F., D. Pontier & M. Artois. 1995. Modelling the Feline Immunodeficiency Virus within populations of domestic cats (Felis catus). Journal of Biological Systems, 3 (3): 769-777.

We attempt to model the circulation of the Feline Immunodeficiency Virus (FIV), a retrovirus analogous to the HIV, within populations of domestic cats. Domestic cats exhibit different patterns of population dynamics, social behaviour and reproductive strategies. In fact, cats can be either solitary or living in large social groups, with many intermediate states.

The aim of the presented model is to provide a conceptualization of the mechanisms of FIV spreading rather than to be a predictive tool. As one of our goals is to integrate easily new informations when available, and to remain simple and close to the biological reality, parameters, such as sex, age classes and dispersion, have been incorporated successively. This model can also be adapted to different types of cat populations by simple changes, as it could be to other host populations. A study of the stability of the model has been done. Based on available data, values of two parameters has been estimated: the carrying capacity and the transmission rate. Results are in good accordance with biological data.

Political perspective on TNR on a university campus

Dombrosky J, Wolverton S. (2014) TNR and conservation on a university campus: a political ecological perspective. PeerJ 2:e312

How to manage the impact of free-ranging cats on native wildlife is a polarizing issue. Conservation biologists largely support domestic cat euthanasia to mitigate impacts of free-ranging cat predation on small animal populations. Above all else, animal welfare activists support the humane treatment of free-ranging cats, objecting to euthanasia. Clearly, this issue of how to control free-ranging cat predation on small animals is value laden, and both positions must be considered and comprehended to promote effective conservation. Here, two gaps in the free-ranging cat—small-animal conservation literature are addressed. First, the importance of understanding the processes of domestication and evolution and how each relates to felid behavioral ecology is discussed. The leading hypothesis to explain domestication of wildcats (Felis silvestris) relates to their behavioral ecology as a solitary predator, which made them suited for pest control in early agricultural villages of the Old World. The relationship humans once had with cats, however, has changed because today domesticated cats are usually household pets. As a result, concerns of conservation biologists may relate to cats as predators, but cat welfare proponents come from the position of assuming responsibility for free-ranging household pets (and their feral offspring). Thus, the perceptions of pet owners and other members of the general public provide an important context that frames the relationship between free-ranging cats and small animal conservation. The second part of this paper assesses the effects of an information-based conservation approach on shifting student’s perception of a local Trap–Neuter–Return (TNR) program in introductory core science classes at the University of North Texas (UNT). UNT students are (knowingly or unknowingly) regularly in close proximity to a TNR program on campus that supports cat houses and feeding stations. A survey design implementing a tailored-information approach was used to communicate what TNR programs are, their goals, and the “conservationist” view of TNR programs. We gauged favorability of student responses to the goals of TNR programs prior to and after exposure to tailored information on conservation concerns related to free-ranging cats. Although these results are from a preliminary study, we suggest that an information-based approach may only be marginally effective at shifting perceptions about the conservation implications of free-ranging cats. Our position is that small animal conservation in Western societies occurs in the context of pet ownership, thus broader approaches that promote ecological understanding via environmental education are more likely to be successful than information-based approaches.

Gene flow between wolf and dog in the Caucasus

Kopaliani, N., Shakarashvili, M., Gurielidze, Z., Qurkhuli, T., & Tarkhnishvili, D. (2014). Gene Flow Between Wolf and Shepherd Dog Populations in Georgia (Caucasus). Journal of Heredity, esu014.

Shepherd dog; first-generation hybrid; wolf 

(all from Kazbegi, Georgia).

Photo courtesy: D. Tarkhnishvili & N. Kopaliani

We studied the distribution of the mitochondrial DNA haplotypes and microsatellite genotypes at 8 loci in 102 gray wolves, 57 livestock guarding dogs, and 9 mongrel dogs from Georgia (Caucasus). Most of the studied dogs had mitochondrial haplotypes clustered with presumably East Asian dog lineages, and most of the studied wolves had the haplotypes clustered with European wolves, but 20% of wolves and 37% of dogs shared the same mitochondrial haplotypes. Bayesian inference with STRUCTURE software suggested that more than 13% of the studied wolves had detectable dog ancestry and more than 10% of the dogs had detectable wolf ancestry. About 2–3% of the sampled wolves and dogs were identified, with a high probability, as first-generation hybrids. These results were supported by the relatedness analysis, which showed that 10% of wolves and 20% of dogs had closest relatives from an opposite group. The results of the study suggest that wolf–dog hybridization is a common event in the areas where large livestock guarding dogs are held in a traditional way, and that gene flow between dogs and gray wolves was an important force influencing gene pool of dogs for millennia since early domestication events. This process may have been terminated 1) in areas outside the natural range of gray wolves and 2) since very recent time, when humans started to more tightly control contacts of purebred dogs.

Herd and shepherd dogs in Georgia

See more about wild canid hybridisation with dogs

Relative effect of cats and other factors in removing rabbits from islands

Flux, J.E.C. 1993. Relative effect of cats, myxomatosis, traditional control, or competitors in removing rabbits from islands. New Zealand Journal of Zoology, 20: 13-18.

The outcome of control on 607 islands of known area round the world was analysed to identify the most effective way of removing rabbits. More islands have been cleared of rabbits by traditionalmethods of trapping, shooting, and poisoning than by introduced predators, competitors, or disease, but their relative efficiency could not be calculated because unsuccessful attempts have not normally been recorded. Where hares were introduced, rabbits subsequently became extinct on 27% of 105 islands; introduction of cats removed rabbits from 11% of 80 islands;myxomatosis from 10% of 119 islands; and cats and myxomatosis together from 3% of 40islands. All these control techniques were more effective on smaller islands than on large ones, but rabbits have “died out” naturally on 11% of the 607 islands, and this factor is not linearly related to island area.

Can we identify cat hybrids throught coat traits?

Ballesteros-Duperón, E., Virgós, E., Moleón, M., Barea-Azcón, J. M., & Gil-Sánchez, J. M.2014.  How accurate are coat traits for discriminating wild and hybrid forms of Felis silvestris?. Mammalia

Hybridisation between domestic cats, Felis catus, and wildcats, Felis silvestris, could lead to the genetic extinction of the latter; therefore, checking hybridisation rates in wild populations is of vital conservation importance. However, detecting hybridisation in the field is particularly challenging. Here, we aim to test the success of morphological-based procedures for discriminating wildcats from their hybrids and domestic cats, against genetic methods. We checked 17 putative Spanish wildcats by using two different classification systems based on coat patterns. None of the putative wildcats analysed in this study seemed to have an admixed genotype. Concordance between genetic and pelage approaches was almost total: only one coat classification produced mixed results with detection of one potential hybrid. Assignment was worse when performed in the field after a rapid examination of coat characters. We conclude that classification systems using coat traits could serve as surrogates of genetic approaches, but only after careful examination of those characters with more discriminatory power. Thus, the control of hybrid populations in the field as a management tool to preserve the genetic identity of wild forms is problematic if based on crude approaches or incomplete classification systems.

Distinctive traits of Wild cat (after Wildcat project)

See more on domestic cat introgression in wildcat

Impact of cats on Australian wildlife

Tidemann, C. R. (1994). Do cats impact on wildlife?. In Urban animal management: proceedings of the third national conference on urban animal management in Australia. Australian Veterinary Association, Sydney.

Cats can have beneficial impacts on wildlife by stabilising numbers of rabbits and exotic rodents. They can also have  adverse impacts, directly through predation and indirectly through the transmission of diseases. In many cases it is incorrect to single out cats as the sole factor responsible for declining wildlife populations, but the adverse impacts of cats may operate in concert with other factors, such as droughts, to finally push species into local or complete extinction. However, there is enough evidence available to indicate that a reduction in the numbers of free-ranging cats in urban areas would lead to a desirable increase in biodiversity in Australian cities. This statement, like any other to do with the management of complex ecosystems, needs to be viewed as a working hypothesis, requiring ongoing evaluation and subsequent modification as further information becomes available. Further information in this case could readily be collected by enlisting the aid of community groups to monitor the response of prey species to cat control programs. 

Urban cat ownership in Baltimore

Childs, J. E. (1990). Urban cats: their demography, population density, and owner characteristics in Baltimore, Maryland. Anthrozoos: A Multidisciplinary Journal of The Interactions of People & Animals, 3(4), 234-244.

A door-to-door questionnaire survey of 430 households in two areas of Baltimore showed significant differences in cat ownership that were attributable to racial composition. Overall, 29.9% of white households owned a mean of 1.9 cats per cat-owning household, compared to 6.8% of black households owning a mean of 1.0 cat per cat-owning household. The mean age of cats was 3.9 yrs and 1.8 yrs in white and black households, respectively. In contrast, dog ownership in the two areas was nearly identical, with 25.6% of white and 29.1% of black households owning a mean of 1.5 and 1.3 dogs per dog-owning household, respectively. Overall, 62.8% of owned cats were spayed/neutered, 51.8% had received a vaccination in the last year, and 34.7% had been wormed during their lifetimes. A total of 31.6% of households allowed their cats to free-range; 42.5% of the 87 owned cats were in this category. The estimated densities of owned free-ranging cats were 7.0 and 2.8 cats per hectare, for the two areas. Driving counts of free-ranging animals in the two areas suggested a larger population of stray or feral cats in the location with lower reported cat ownership.

Humans and stray cats in NY

Haspel, C., & Calhoon, R. E. (1990). The interdependence of humans and free-ranging cats in Brooklyn, New York. Anthrozoos: A Multidisciplinary Journal of The Interactions of People & Animals, 3(3), 155-161.

Based on the responses of 177 participants in a survey conducted in Brooklyn, New York, it was ascertained that 22.0% of the respondents fed free-ranging cats (2.8% daily and 19.2% occasionally). The food provided by feeders alone was estimated to support 1.71 to 2.10 cats per acre (4.2 to 5.2 cats per hectare), a density that is 1.35 times greater than the actual cat population. Other resources provided (e.g., shelter, medical help, adoption) were also estimated. Daily feeders were devoted to their cats. They continued to feed them despite the disapproval of their neighbors, financial constraints, or social obligations. Free-ranging cats appear to be in a mutually life-enhancing relationship with their feeders.

Home range of free-roaming cats in NY

Haspel, C. & R.E. Calhoon. 1989. Home ranges of free-ranging cats (Felis catus) in Brooklyn, New York. Canadian Journal of Zoology, 67: 178-81.

Home range size is stable among free-ranging cats in Brooklyn, New York. Marked male and female cats had mean home ranges of 2.6 (95% CI, 2.38–2.87) and 1.7 ha (95% CI, 1.57–1.98), respectively, as estimated by the population utilization distribution. Males had significantly larger home ranges, used the perimeter of their ranges more, and had greater variability in home range size than females. Gender differences in body weight accounted for observed differences in home range size; the seeking of estrous females by males could not account for differences in male and female home ranges. The availability of garbage or abandoned buildings, neighborhood, season, or experimental supplementary feeding did not influence home range size.

Feral house diet in Victoria

Coman, B. J., & Brunner, H. (1972). Food habits of the feral house cat in Victoria. The Journal of Wildlife Management, 36 (3): 848-853.

A total of 128 feral domestic cats (Felis catus) were collected from two different habitat types in Victoria. The stomachs of 80 of these cats contained food. Mammals, chiefly rabbits (Oryctolagus cuniculus), small murids, and phalangers, comprised some 88 percent, by volume, of the total dietary intake. Birds, cold-blooded vertebrates, and invertebrates were of secondary importance in the diet, accounting for only 5.2 percent, by volume, of the total intake. Grass and small twigs occurred frequently in the stomachs, but the volume represented was small (1.4 percent). Other items, mainly carrion and cat fur, accounted for 5.4 percent of the intake on a volume basis. Feral cats from undeveloped bush areas relied heavily on small indigenous mammals, whereas rabbits and house mice (Mus musculus) were the main mammalian prey species eaten in improved and semi-improved agricultural areas. Remains of indigenous mammals were not found in the stomachs of cats from the latter areas. It appears that feral cats are opportunist predators and scavengers and that the level of predation on any one prey type will depend largely on its relative availability. As a consequence, predation on native mammals is probably limited to those undeveloped areas of bush and scrub where such species are more plentiful.