Cat predation on wildlife

Cats hunt small prey, and both feral and domesticated cats prey on wildlife. This is sometimes seen as a desirable phenomenon, such as in the case of barn cats and other cats kept for the purposes of pest control. In other cases, the effect of cats on wildlife is met with concern.

Mice and rats

For thousands of years, cats have been known for their ability to hunt mice and rats and keep their populations under control. This ability is understood as the reason cats became domesticated.[1] :68 The relationship was more of convenience (or mutualistic) than dependence: "Cats killed mice and rats, and humans provided lots of mice and rats to kill since mice and rats lived in human settlements."[1]:68 A 2014 study examining 5,300 years of cat remains in an agricultural village of Quanhucun, China, provides early evidence of this dynamic, where cats protected grain stores by eating rodents.[2][3]

If they are well-fed, farm cats are more dependable as effective ratters, as they are less likely to stray or hunt further afield.[4]:110 Cats are wary of adult rats, given their size,[4]:111 but are particularly adept at hunting young rats.[4]:110

In 2002, feral cats introduced to a flower market in Los Angeles, California, were noted to have helped lower rat populations.[5] In Chicago's 47th Ward, feral cats were introduced in 2012 to help the city deal with the rat problem there.[6]

Efforts to eradicate feral cats in Ventura, California, were noted in 2002 to have resulted in increasing numbers of rats, which were being monitored for health problems such as bubonic plague.[5][7]

Birds

A 2013 study by Scott R. Loss and others of the Smithsonian Conservation Biology Institute and the U.S. Fish and Wildlife Service suggested that free-ranging domestic cats (mostly unowned) are the top human-caused threat to wildlife in the United States, killing an estimated 1.3 to 4 billion birds and 6.3 to 22.3 billion mammals annually.[8][9] These figures were much higher than previous estimates for the U.S.[8]:2 Unspecified species of birds native to the U.S. and mammals including mice, shrews, voles, squirrels and rabbits were considered most likely to be preyed upon by cats.[8]:4

Advocates for feral cats counter that Loss's study and earlier related studies have inflated estimates of wildlife killed by cats in the U.S., based on unscientific research that extrapolates from tiny samples and projects them onto whole nations.[10] One reviewer stated that Loss's study was filled with "numerous major flaws in the statistical arguments made" that in his view made it "unacceptable for publication".[11]:1 It was unclear how predation rates were obtained, and then "applying these estimates to all cats across the country is highly questionable."[11]:3 Extrapolation was also misused when "Based on a small sample of cats over three summer months in one specific geographic area, the authors see fit to extrapolate this predation rate to all cats at all times of the year in all geographic regions in the United States."[11]:3

Perhaps the first U.S. study that pointed to predation by cats on wildlife as a concern was ornithologist Edward Howe Forbush's 1916 report for the Massachusetts State Board of Agriculture, The Domestic Cat: Bird Killer, Mouser and Destroyer of Wildlife: Means of Utilizing and Controlling It.[12]

U.K. biologist and cat behaviour expert Roger Tabor states that "studies from all around the world have found that cats catch relatively few birds compared to small mammals."[13]:135 The Royal Society for the Protection of Birds states that there is no scientific evidence that cat predation "is having any impact on bird populations UK-wide."[14] Moreover, city cats have smaller ranges. In his research, Tabor found "the average annual catch of the average London cat to be two items instead of the fourteen of a village cat."[13]:135 Tabor comments about some of the challenges of stalking birds for cats: "From the cat's point of view not only do birds not play fair by flying and having eyes that can see beyond the back of their heads, but they can positively cheat by using loud alarm calls and throw the cat's chances of catching any others."[4]:123

Island settings pose particular challenges for wildlife. A 2001 study identified cats alone as responsible for the plight of some island bird species, such as the Townsend's shearwater, socorro dove, and the Marquesan ground dove.[15][15]:400 The same study identified the greatest cause of endangerment of birds as habitat loss and degradation, with at least 52% of endangered birds affected,[15]:399 while introduced species on islands, such as domestic cats, rats and mustelids,[15]:403 affected only 6% of endangered birds.[15]:399 Other studies caution that removing domestic cats from islands can have unintended consequences, as increasing rat populations can put native bird[16] and mammal species[17][18] at risk.

Impact by location

Australia

Cats in Australia have been found to have European origins.[19] This is important to note, because of their affect on native species. Feral cats in Australia have been linked to the decline and extinction of various native animals. They have been shown to cause a significant impact on ground nesting birds and small native mammals.[20]

Feral cats have also hampered any attempts to re-introduce threatened species back into areas where they have become extinct as the cats have hunted and killed the newly released animals.[21] Numerous Australian environmentalists claim the feral cat has been an ecological disaster in Australia, inhabiting most ecosystems except dense rainforest, and being implicated in the extinction of several marsupial and placental mammal species.[22]

New Zealand

The fauna of New Zealand has evolved in isolation for millions of years without the presence of mammals (apart from a few bat species). Consequently, birds dominated the niches occupied by mammals and many became flightless. The introduction of mammals after settlement by Māori from about the 12th century had a huge effect on the indigenous biodiversity. European explorers and settlers brought cats on their ships and the presence of feral cats were recorded from the latter decades of the 19th century.[23] It is estimated that feral cats have been responsible for the extinction of six endemic bird species and over 70 localised subspecies as well as depleting bird and lizard species.[24]

United Kingdom

In the U.K., The Royal Society for the Protection of Birds states that there is no scientific evidence that cat predation "is having any impact on bird populations UK-wide. This may be surprising, but many millions of birds die naturally every year, mainly through starvation, disease, or other forms of predation. There is evidence that cats tend to take weak or sickly birds ... Those bird species that have undergone the most serious population declines in the UK (such as skylarks, tree sparrows and corn buntings) rarely encounter cats, so cats cannot be causing their declines. Research shows that these declines are usually caused by habitat change or loss, particularly on farmland."[14] This evidence is despite the common practice in the U.K. of allowing owned cats access to the outdoors,[25] which is recommended to prevent feline obesity (p. 138) and behavior problems and other health problems arising from confinement stress (p. 121).[13]

Islands

Consequences of introduction

The Stephens Island wren became extinct within two years of the introduction of cats to Stephens Island.

Many islands host ecologically naive animal species. That is, animals that do not have predator responses for dealing with predators such as cats.[26] Feral cats introduced to such islands have had a devastating impact on these islands' biodiversity.[27]

They have been implicated in the extinction of several species and local extinctions, such as the hutias from the Caribbean, the Guadalupe storm petrel from the Pacific coast of Mexico, and the Stephens Island wren. In a statistical study, they were a significant cause for the extinction of 40% of the species studied.[27] Moors and Atkinson wrote, in 1984, "No other alien predator has had such a universally damaging effect."[26]

Feral cats, along with rabbits, some sea birds, and sheep, form the entire large animal population of the remote Kerguelen Islands in the southern Indian Ocean. Although exotic mammals form the bulk of their diet, cats' impact on seabirds is very important.[28]

Restoration

Because of the damage cats cause in islands and some ecosystems, many conservationists working in the field of island restoration have worked to remove feral cats. (Island restoration involves the removal of introduced species and reintroducing native species.) As of 2004, 48 islands have had their feral cat populations eradicated, including New Zealand's network of offshore island bird reserves[29] and Australia's Macquarie Island.

Larger projects have also been undertaken, including their complete removal from Ascension Island. The cats, introduced in the 19th century, caused a collapse in populations of nesting seabirds. The project to remove them from the island began in 2002, and the island was cleared of cats by 2004. Since then, seven species of seabird that had not nested on the island for 100 years have returned.[30]

In some cases, the removal of cats had unintended consequences. An example is Macquarie Island, where the removal of cats caused an explosion in the number of rabbits, rats, and mice that harm native seabirds[31][32][33] even if the eradication was positioned within an integrated pest management framework.[34] The removal of the rats and rabbits was scheduled for 2007 and it could take up to seven years and cost $24 million.[35]

Hybridisation with wild felids

Feral cats have interbred with wildcats to various extents throughout the world, the first reported case occurring more than 200 years ago. The significance of hybridisation is disputed. Older documentation suggests that the wildcat was a separate species from the domestic cat, but modern genetic analysis[36] has shown that the domestic cat is a domesticated version of the near-eastern wildcat (Felis silvestris lybica). In some locations, high levels of hybridisation have led to difficulties in distinguishing a "true" wildcat from feral domestic and domestic hybrid cats, which can complicate conservation efforts.[37] Some researchers argue that "pure" wildcats do not exist anymore, but others dispute this.[38]

One study in Scotland suggests that while "true" Scottish wildcats are unlikely to exist, the current wildcat population is distinct enough from domestic cats to be worth protecting,[39] genetics research is still underway as part of the Wildcat Haven project in Scotland, which has reported success protecting wildcats from hybridisation with widespread trap-neuter-return work.[40] Wildcat populations' notable gene introgression exists also in Italy, Hungary, Spain and Portugal.[41] For a discussion of this issue see The Encyclopedia of Mammals, OUP, pages 656–657.[42]

See also

References

  1. 1 2 Grandin, Temple and Johnson, Catherine (2009) Animals Make Us Human: Creating the Best Life for Animals, Mariner Books, ISBN 9780151014897.
  2. ↑ "Ancient Chinese cat bones shake up domestication theory". The Guardian. 17 December 2013.
  3. ↑ Hu, Y.; Hu, S.; Wang, W.; Wu, X.; Marshall, F. B.; Chen, X.; Hou, L.; Wang, C. (2013). "Earliest evidence for commensal processes of cat domestication". Proceedings of the National Academy of Sciences 111: 116–120. doi:10.1073/pnas.1311439110.
  4. 1 2 3 4 Tabor, Roger (1983) The Wild Life of the Domestic Cat. Arrow Books. ISBN 0099312107.
  5. 1 2 LeDuff, Charlie (17 September 2002). "Up, Down, In and Out in Beverly Hills: Rats". The New York Times.
  6. ↑ "North Side’s 47th Ward Using Feral Cats To Catch Rats", CBS Chicago, 28 June 2012.
  7. ↑ Blanchard, Jessica (9 September 2002). "With the Cats Away, Beachfront Rodents Have a Field Day". Los Angeles Times.
  8. 1 2 3 Loss, Scott R.; Will, Tom; Marra, Peter P. (2013). "The impact of free-ranging domestic cats on wildlife of the United States". Nature Communications 4: 1396. doi:10.1038/ncomms2380. PMID 23360987.
  9. ↑ Morelle, Rebecca (29 January 2013). "Cats killing billions of animals in the US". BBC News. Retrieved 12 February 2013.
  10. ↑ "Setting the Record Straight", Alley Cat Allies, links to fact sheets and articles critiquing several studies.
  11. 1 2 3 "A review of the statistical methods employed in the article 'The impact of free-ranging domestic cats on wildlife of the United States'", Gregory J. Matthews, prepared for Alley Cat Allies, 4 March 2013.
  12. ↑ Edward Howe Forbush, "The Domestic Cat: Bird Killer, Mouser and Destroyer of Wildlife: Means of Utilizing and Controlling It", Commonwealth of Massachusetts, State Board of Agriculture, Economic Biology Bulletin 42, 1916.
  13. 1 2 3 Tabor, Roger (2003) Understanding Cat Behavior. David & Charles Ltd. ISBN 9780715315897.
  14. 1 2 "Are cats causing bird declines?" The Royal Society for the Protection of Birds, accessed 23 June 2014.
  15. 1 2 3 4 5 Collar, N. J. (2001). Endangered Birds (PDF) 2. New York: Academic Press. p. 400. in Encyclopedia of Biodiversity
  16. ↑ "Cats protecting birds revisited.", M. Fan et al., Bull. Math Biol. September 2005, 67(5), pp. 1081–106.
  17. ↑ "Island mammal extinctions are determined by interactive effects of life history, island biogeography and mesopredator suppression", Emily Hanna et al., Global Ecology and Biogeography, Vol 23, Issue 4, 11 August 2013.
  18. ↑ Popkin, Gerald (29 August 2013). "Feral cats help some endangered mammals survive, report says". The Sydney Morning Herald.
  19. ↑ Spencer, Peter B.S. (9 November 2015). "The Population Origins and Expansion of Feral Cats in Australia" (PDF). American Genetic Association. doi:10.1093/jhered/esv095. Retrieved 15 February 2016.
  20. ↑ Dickman, Chris (May 1996). Overview of the Impacts of Feral Cats on Australian Native Fauna (PDF). The Director of National Parks and Wildlife – Australian Nature Conservation Agency – Institute of Wildlife Research. ISBN 0-642-21379-8. Retrieved 11 February 2013.
  21. ↑ The Threat Of FeralCats. Environment.nsw.gov.au (28 October 2011). Retrieved on 5 May 2013.
  22. ↑ Robley, A. Reddiex, B. Arthur T. Pech R. Forsyth, D. (Sep 2004). "Interactions between feral cats, foxes, native carnivores, and rabbits in Australia" (PDF). CSIRO Sustainable Ecosystems / Arthur Rylah Institute for Environmental Research. Archived from the original (PDF) on 17 March 2011. Retrieved 12 February 2013.
  23. ↑ King, Carolyn (1984) Immigrant Killers. Auckland: Oxford University Press. ISBN 0-19-558121-0
  24. ↑ Eason, Charles T.; Morgan, David R. and Clapperton, B. Kay (1992). Toxic bait and baiting strategies for feral cats. University of Nebraska – Lincoln: Proceedings of the Fifteenth Vertebrate Pest Conference 1992.
  25. ↑ "In the UK, the vast majority of pet cats have free access to the outside world, or are at least allowed to go outside unsupervised for large parts of the day." "A world of difference – How cat ownership in America differs to the UK", Pets4Homes, accessed 1 September 2014.
  26. 1 2 Moors, P.J.; Atkinson, I.A.E. (1984). "Predation on seabirds by introduced animals, and factors affecting its severity" in Status and Conservation of the World's Seabirds. Cambridge: ICBP. ISBN 0-946888-03-5.
  27. 1 2 Barcott, Bruce (2 December 2007). "Kill the Cat That Kills the Bird?". The New York Times.
  28. ↑ Pontier, D., L. Say, F. Debias, J. Bried, J. Thioulouse, T. Micol & E. Natoli (2002). "The diet of feral cats (Felis catus L.) at five sites on the Grande Terre, Kerguelen archipelago" (PDF). doi:10.1007/s00300-002-0424-5.
  29. ↑ Nogales, Manuel; Martin, Aurelio; Tershy, Bernie R.; Donlan, C. Josh; Veitch, Dick; Puerta, Nestor; Wood, Bill; Alonso, Jesus (2004). "A review of feral cat eradication on islands" (PDF). Conservation Biology 18 (2): 310–319. doi:10.1111/j.1523-1739.2004.00442.x.
  30. ↑ Cat eradication from Ascension Island. Petsaspests.blogspot.com (2014-01-23). Retrieved on 2015-11-01.
  31. ↑ "Up against rats, rabbits and costs". The Sydney Morning Herald. 12 April 2007.
  32. ↑ Fears for sub-antarctic island plagued by rabbits. ABC News (15 July 2006).
  33. ↑ Draper, Michelle and La Canna, Xavier (14 January 2009) Cat kill devastates Macquarie Island. Nine News
  34. ↑ Controversy on feral cat removal on Macquarie Island. Petsaspests.blogspot.com.es (2013-05-14). Retrieved on 2015-11-01.
  35. ↑ Macquarie Island World Heritage Area. Plan for the Eradication of Rabbits and Rodents on Macquarie Island. Parks and Wildlife Service, Tasmania. parks.tas.gov.au
  36. ↑ Driscoll, C. A.; Menotti-Raymond, M.; Roca, A. L.; Hupe, K.; Johnson, W. E.; Geffen, E.; Harley, E. H.; Delibes, M.; Pontier, D.; Kitchener, A. C.; Yamaguchi, N.; O'Brien, S. J.; MacDonald, D. W. (2007). "The Near Eastern Origin of Cat Domestication". Science 317 (5837): 519–523. doi:10.1126/science.1139518. PMID 17600185.
  37. ↑ European wildcat (Felis silvestris grampia) Arkive.org
  38. ↑ "CSG Species Account: European Wildcat". Cat Specialist Group. 1996. Archived from the original on 8 March 2013. Retrieved 7 January 2016.
  39. ↑ Genetic diversity and introgression in the Scottish wildcat. Molecular Ecology (2001) 10: 319–336. Archived 17 May 2008 at the Wayback Machine.
  40. ↑ (Herald Scotland 'Haven to Save the Wildcat from Total Extinction')
  41. ↑ Domestic gene introgression into wildcat populations in Europe. Petsaspests.blogspot.com.es. Retrieved on 2015-11-01.
  42. ↑ The Encyclopedia of Mammals, OUP, ISBN 978-0-19-920608-7, pages 656–657
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