Feral Domestic Cats Stay Close To Humans
    By Caitlin Kight | October 23rd 2011 02:02 PM | 4 comments | Print | E-mail | Track Comments
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    Of all the domestic animals that can potentially harm wildlife, cats (Felis catus) may be the most problematic. They are thought to kill billions of wild birds each year, along with many other small prey, such as mice and voles. In so doing, they steal potential food resources from other wild animals--including mammalian, avian, and reptilian carnivores. Additionally, cats may hybridize with close relatives, including wildcats (Felis silvestris) and other small feline species such as the Iberian lynx (Lynx pardinus)--the latter of which is considered by some to be the most critically endangered wild cat in the world. When they encounter other animals in the wild, cats can pass on infectious diseases, such as feline immunodeficiency virus and feline leukemia virus.

    (Feral cat, Felis catus, the state of whose ears is evidence of how rough life can be on the streets)

    Domestic cats are present on all continents and on a number of islands. They are particularly common in urban and suburban areas, and are generally found near human establishments. Feral cats can exist in staggering numbers; in the U.S. alone, there are thought to be some 30 million cats living in the wild. Many of these may receive some food support from humans, either through direct feeding or in the form of garbage that can be picked through for tasty leftovers. Where this does not happen, however, the animals may have quite large home ranges over which they travel in search of sustenance. This can interfere with conservation efforts when the cats' wanderings take them through natural areas inhabited by protected animals upon which they might prey, or other feline species with which they can interbreed.

    One such area is the Moura-Barrancos Nature 2000 site in southeastern Portugal, near the Spanish border. Part of this habitat has been named as a Bird Special Protection Area; it is also one of the few remaining places where Iberian lynx can be found in Portugal. In order to understand the impact that domestic cats might have on native animals living in the Nature 2000 site, collaborators from the Centro de Biologia Ambiental, the Estación Biológica de Doñana Consejo Superior de Investigaciones Científicas, and the Universidade de Aveiro Campus Universitário de Santiago undertook a study in which they investigated the natural and anthropogenic factors associated with the presence, abundance, and use of space by domestic cats. The researchers used a combination of live-trapping, photo-trapping, and radio-tagging techniques in order to determine where cats were living and how far they roamed. To characterize the areas inhabited by feral cats, the scientists collected data on a variety of habitat variables (including type of land cover, slope of terrain, and the presence of roads and rivers), as well as performing survey transects in order to determine what other carnivores could be found within each cat territory.

    (Feral kittens may look cute and innocent, but even they are capable of impacting local wildlife populations.)

    Although the Nature 2000 site does not contain any villages, 128 traditional farms are scattered throughout the area. The bulk of these (67.2%) have no residents, and many are abandoned or in complete ruin. No cats were found at these farms, or in the secluded natural areas surveyed by the researchers. On the other hand, cats were easily detected and captured at active farms--specifically, 130 cats were found across the 42 active farms, yielding a density of 0.26 cats per square kilometer. Among cats that could be sexed, there were about twice as many females as males. None of these individuals was deliberately kept as a pet, and none received veterinary attention; however, approximately 85% of these animals were occasionally given food by people at the farms. Despite this, all but one of the cats was described as "very wary" and could not be closely approached or caught by hand.

    The researchers constructed mathematical models investigating which habitat characteristics were most closely associated with the presence of cats. The best model describing patterns across all territories combined indicated that cats were likely to be found where there were both people and habitat characteristics that represent the suitability of habitat for anthropogenic use (including both roads and rivers). On a per-farm basis, cat presence was (unsurprisingly) associated with the presence of, and food supplementation by, people.

    Eight of the live-trapped cats (5 males and 3 females) were given radio collars prior to release. The resultant tracking data indicated that each cat's home range included the farm where it was captured, and was centered on farm buildings. Male home range sizes were nearly 5 times as large as those of females--not surprising given that they roam far and wide, particularly during the mating season, in order to find females. One male traveled as far as 6 km, but in general the cats did not move more than 3 km at a time; multiple farms were used as "stepping stones" when the animals moved long distances. During their movements through the habitat, cats preferentially spent time in human areas and flat sites within 200 m of roads. Conversely, they avoided steep areas that were far from roads and covered with natural vegetation. Daily movements were most closely associated with the probability of encountering red foxes (Vulpes vulpes), which cats avoided out of fear of predation.

    (During encounters like these, feral cats can transmit diseases such as feline immunodeficiency virus and feline leukemia virus, which they can also pass on to wildlife.)

    The results of the study consistently indicated that, despite their ability to fend for themselves, domestic cats did not live independently of humans--or, if they did, were present in very low numbers. However, even though they were closely associated with anthropogenic areas, cats often passed through natural habitats during their daily travels or when roaming to find mates. These findings have two major conservation implications. First, cat management efforts should be focused on human settlements, since this is where cats are most likely to be found in high numbers. A combination of techniques may be useful for curtailing feral cat populations--including outlawing feeding, preventing access to refuse, neutering males, increasing the number and size of natural vegetation patches, and promoting the presence of natural competitors such as foxes. Second, planners should consider the impacts of erecting anthropogenic structures in or near natural areas, since these will likely attract feral cats and/or act as stepping stones, linking otherwise unconnected cat habitats and facilitating spread of the animals into new areas.

    The authors also emphasize the importance and utility of education as a conservation tool. For instance, farmers should be encouraged to provide habitat for barn owls (Tyto alba), which, like cats, help control rodent populations--but which, unlike cats, are a native species.


    For supplementary images associated with this post, check out the Anthrophysis pin board at Pinterest.

    Ferreira, J.P., Leitão, I., Santos-Reis, M., Revilla, E. 2011. Human-related factors regulate the spatial ecology of domestic cats in sensitive areas for conservation. PLoS ONE: 6(1):e25970.

    Thanks to the following websites for providing the images used in this post:



    Gerhard Adam
    A combination of techniques may be useful for curtailing feral cat populations--including outlawing feeding, preventing access to refuse, neutering males, increasing the number and size of natural vegetation patches, and promoting the presence of natural competitors such as foxes.
    This is another prime example of human pet owners being irresponsible by failing to spay/neuter their pets and then disposing of them when they become inconvenient.  It also needs to be remembered that many cat owners have no problem with the idea that their cats roam free, so while they are not feral, they are also not "invisible" and will interact in the same way as feral cats do with the environment.

    As a practical matter, cats are convenient for rodent control.  Just from my own experience, cats freely move around in areas where rats/mouse tend to accumulate (hay rooms, etc.) and by not requiring anything special, are useful to help control those populations. 

    Mundus vult decipi
    In spite of your challenge to Dauphine's "science," one of the links to "Related Articles on Science 2.0" is to an article by a Caitlin Kight. The article is titled "Feral Domestic [sic] Cats Stay Close to Humans" and (in addition to repeated misuse of the word "anthropogenic") contains the claim that cats kill not a "billion" wildlife creatures per year, but "billionS" of wildlife animals per year. Why critique a fallacious claim in one article, then promote the same claim in another article? (I also question the data in Kight's article behind her allegation that domestic cats hybridize with other species such as lynxes. Are there data that support this claim? My hypothesis would be that domestic cats are more likely to be predated upon by felids like lynxes.)

    There are hugely varying estimates of how many wild birds cats kill each year. In the US alone, the number has been calculated at just under 2 billion; if this is correct, the worldwide total would be "billions." However, nobody knows any of this for sure and the totals are generally produced by approximating how many cats there are, approximating how many birds the average cat kills in a year, and then multiplying the two figures together. So, the actual tally could be quite a bit smaller (not all cats like hunting birds, for instance), but it could also be quite high (e.g., if many cats specialize in wiping out nests full of chicks all in one go). Note that this estimate is only for birds--I have no idea how high the figure goes once you also consider additional prey items such as the perennial favorites, moles and voles.

    The claim about cat-lynx hybrids was one made by the authors of the paper and was supported by previous scientific work; there are several confirmed instances but, as far as I know, many involve Old World lynxes--some of which are quite a bit smaller than cougars. I do not know much more than that, but I would imagine that you are correct that wild cats would be quite happy to predate domestic cats--especially outside of the breeding season when other urges are less intense.

    Not that it really matters, but my use of the word "anthropogenic" in this context is acceptable as far as human disturbance biologists are concerned. The word is commonly used by conservationists and biologists to mean "human-related," or even to act as a synonym for "human," in addition to its traditional dictionary definition of "caused or produced by humans." Etymologically unsound, perhaps, but true nonetheless. I assume that this is different from how it is used in your field, but I suppose that is just another case of different groups of researchers using the same terms in different ways ("noise," "information," and "frequency" are others that I commonly come across).
    NSF Postdoctoral Researcher, University of Exeter--Tremough Campus, UK. Personal website:
    I am sure I saw a lynx on my recent trip to the Algarve and I have taken a distant photo of it. It was late evening and it was standing in a walled field with wild hills in the background. It was the size of a small deer, and stared at me for a while before running like a leopard and disappearing. It was sunset and I was taking photos of almond trees and went down a quiet track to get a better photo when I saw the cat and it saw me. Who would be interested in my photo and knowing about this sighting? Linda