Wednesday, June 12, 2013

A Cat in Hand is Worth Keeping Out of the Bush


Carnage. Photo courtesy: http://blogs.scientificamerican.com/culturing-science/files/2013/01/cat-eats-bird.jpg
It is widely known that biodiversity is declining worldwide, and many of the causes are believed to be anthropogenic. We use too much electricity, water, and land, and we often pollute the areas of nature that we're not directly exploiting. Well, one of the ways that we can pollute environments is by introducing a foreign species. More often than not, these usually accidental introductions end with that species being unable to become established in their new environment and they die out, however, in the instances where a species is able to invade permanently, many problems can arise.

Across the American South, from which I hail, kudzu has completely engulfed hillsides. In the Northwest, where I currently live, nutria have extirpated some competitors and harmed vegetation. Perhaps the most deadly and environmentally harmful introduced species, however, is a familiar face, the house cat (Felis catus). Historically, cats have been used by humans to control rodent and other small mammal pests, and have been introduced across the world to practically every environment inhabited by humans. This seems like a natural and innocuous way to keep food stores safe from pilfering, but the truth is that cats kill an estimated half billion birds per year in America alone (according to the American Bird Conservancy). In a recent study (Balogh et. All), cats were found to be the major cause of mortality for birds in the suburbs, and in particularly cat-dense areas, the bird population was predicted to be unable to maintain itself, facing such heavy predation. To add a further wrinkle to this problem, cats can often outcompete local predators such as weasels, hawks, skunks, foxes, or raccoons by eating their prey right out from under them. Although cats are adaptable and efficient predators, the reasons they can so often outmuscle the local talent are, again, mostly due to humans. Humans protect cats from predation, disease, and prey shortage (due to their supplemental food from humans), which are some of the main factors that keep native predator populations from exploding in the same way that wild cat numbers can. Paradoxically, and unlike some predators, simply giving your cat adequate food is not enough; their drive to hunt remains strong, so even a well-fed cat is a threat to its environment (Coleman et. All).
Look at this lazy bastard. LaceMaurice and photo courtesy: me
In North America, birds have always been evolving in the presence of mammalian predators, so perhaps that is why we've not heard much about cat-driven bird declines here. However, on islands, the environment is often very fragile, almost precarious. Any small perturbation from the equilibrium reached on an isolated island environment can and often does lead to major shifts in the system, with invaders regularly overexploiting a habitat that has evolved no defense to them. A famous example of this kind of island mayhem is the brown tree snake decimating the native bird population of Guam upon introduction, leading to the extinction of 12 native species. For this reason, cats are an even bigger threat to biodiversity down under in Australia, whose largest native mammalian predator, the quoll, only reaches about 13-15 lbs in weight. The situation is even more serious in New Zealand; not only due to the fact that Kiwis own the most cats per capita in the world, but the nation's endemic, unique, and often flightless bird fauna evolved without a single mammalian predator. In Australia, quolls have been most badly hurt by cats in their competition for small prey, with an estimated 4 million kills of wildlife per year attributed to cats. Since the introduction of cats (and humans) to the continent, all species of quoll have declined drastically, each of four species being now listed as either vulnerable or threatened under the Environment Protection and Biodiversity Conservation Act. In New Zealand things are even worse, with multiple bird species going extinct since the invasion of cats and other mammalian predators, and some species like the black robin, kakapo, and even the iconic kiwi barely scraping by, with a future that is anything but secure.
Hope emerges. Photo source below**

Facing this threat to the native wildlife of his country, Gareth Morgan, a New Zealander economist, sees no other answer short of ridding the country of cats completely. This proposal sounds crazy, especially in America where cats are known to negatively affect wildlife but have caused no widely publicized extinctions, and are well liked across the country. However, the movement is starting to gather support, once more people learn about the damage that cats can do to New Zealand, and the dire situations some of the countries beloved native birds are facing. Morgan advocates not only keeping cats indoors, but just plain not replacing them when they pass away (also, he does not advocate the killing of pet cats!). He argues that keeping cats cooped up indoors is also not ideal, and is unfair to the cat, and that if they are let outside it is inevitable that they will cause environmental casualties. This is part of why he views getting cats completely out of the country as the only real solution, it is unrealistic to keep cats inside 24/7, and equally delusional to think that they won't cause trouble when they do get out. Additionally, Morgan takes issue with the SPCA's policy of “TNR,” which stands for Trap-Neuter-Release. The SPCA claim that feral/stray cat colonies cannot grow if they cannot breed, and will therefore eventually die out, but Morgan contests that this requires 100% sterilization and no more cats to be released into the area by humans or introduced by other means, which is not a reasonable assumption. Morgan's stance on the issue can be summed up as “we have to exterminate feral cat populations or they will exterminate (and drive extinct!) our treasured native birds.” Now, I am loathe to advocate the killing of cats, but I agree that, especially in deli-cat island environments, feral cats have to go before they cause more damage to other species. They should be treated as any invasive pest would be in these areas, and when the facts are laid out, something has to die. I would rather protect unique wildlife and environments than continue to turn a blind eye to the destruction caused by cats, giving them a free pass because of how much we like them!
This is a serious issue. Photo courtesy: http://www.seriouscat.com/

Cat References:
http://garethsworld.com/catstogo

http://biodiversityconservationblog.wordpress.com
/2013/05/27/cats-versus-native-cats/

http://www.nytimes.com/2011/03/21/science
/21birds.html?_r=2&ref=us&

http://nationalzoo.si.edu/scbi/migratorybirds
/science_article/pdfs/55.pdf

http://web1.cnre.vt.edu/extension/fiw/wildlife/damage
/Cats.pdf

**Kakapo photo courtesy: http://farm9.staticflickr.com/8257/8603274390_8c360c4248.jpg

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