Predation on wildlife is one of the more controversial domestic cat issues today. That is to say, emotions run very high and there are two extremely polarized interest groups:
- Conservationists cite horrific statistics about the effects house cats have on wildlife, up to and including statistics like “millions” and “billions” of lost prey animals in some some studies. (McDonald and others)
- Pet owners simply say “Not my cat.” Nuances range from “my cat doesn’t do that” to “hands off my cat.”
At this point, even though government agencies are involved and some places have passed cat control legislation, owners overall seem to be holding.
In order to sway cat lovers, researchers who support such laws now emphasize welfare issues – the risk of road accidents, etc., if cats are let outside – instead of predation on wildlife. (Hall and others; McDonald and others)
The basic problem here is that domestic cats are both adorable pets and very efficient carnivores. We have always used cats for both these purposes, and each of these two very different parts of the feline nature inspires strong emotions.
Non-cat-lovers appreciate the pest control but don’t understand the affection people pour out on these little hypercarnivores.
We cat lovers freak out if Fluffy brings in a dead animal, and we ignore the very clear fact that house cats are the dominant small predator in any human-dominated environments.
Zoologists can’t ignore that unpleasantness. The numbers they crunch come from data showing, for example, that 63 animal species (26% of all extinctions today, according to Doherty and others) have already been completely wiped out by domestic cats. This is why they turn to the state–it’s hard for them not to get frustrated over what seems like blindness in cat owners.
We’re not blind, really. We just are wary of any conservation argument that involves killing cats, especially when it appears to be the obvious solution. There are plenty of historical bad examples we could point to for support of this position.
A recent one that doesn’t involve literal demons and witches happened in Singapore where, despite lack of solid evidence, street cats were culled out of fear that they might spread SARS.
Only afterwards was it discovered that domestic cats, feral or owned, have nothing to do with SARS. But those beloved animals cannot be revived and reinserted into Singapore’s complex urban ecosystem. As far as I can tell, no one is even looking at what effect(s) this sudden removal of a top predator had there.
History also shows many examples of hoarding and other ways cat owners sometimes go off the deep end. And we can’t ignore those 60-plus extinct species correctly chalked up to cat predation.
We need to admit that cats can be serious environmental threats.
And conservationists need to look at the practical, ecological, and ethical concerns that some experts have with lethal control. (Doherty and Ritchie)
It wouldn’t hurt for them also to acknowledge that someone who loves a cat probably cares a lot about other animals, too–including local wildlife. We just don’t like getting clobbered with statistics, especially when it’s to change how we view a situation that has political aspects.
Of course, I’m prejudiced. Still, I can see that few stakeholders seem interested in just talking it over. Yet there is plenty of room on the middle ground, if each side can accept that the other has a point.
My review of the literature hasn’t been anything like comprehensive, but I have found three supporters of this approach.
Robertson, who focused on feral cats in 2008, takes down the “cats are non-native predators disrupting an ecosystem” argument by pointing out that most farm animals are non-native, too, and no one has a problem with controlling native predators that attack them. At the same time, she agrees that wildlife is going to suffer if you let your cat out.
Turner, in 2014, flat out says, “Both sides . . . should view evidence before making hasty judgements.”
He addresses flaws in some studies, including mixing different types of statistics, failing to take into account where the study was done, and some factors that skew the results.
Fitzgerald and Turner (2000) note that, when cranking the numbers, you have to consider the combined effects of all predators, not just domestic cats. And cat predation studies rarely use the typical scientific method of dividing feline hunters into two groups: the study group, which is manipulated to test hypotheses, and a control group that is left alone.
Turner (2014) also says that what is observed locally might not be true across every habitat–you can’t just extrapolate to get “millions” and “billions.” As well, estimates of “total predation” are meaningless unless you also take into account the entire population of a prey species and its annual production rate.
Nevertheless, he is in favor of removing cats from islands or restricting them indoors to protect sea birds. If there are other mammals on an island, like rats, mice, or rabbits, cats will leave most of the birds alone, but if not, they easily switch to birds, with devastating results.
Rabbits may not be the first mammal that comes to mind when you think of small islands, but they were an important factor in one of the most famous examples of how challenging conservation and predator control can be.
Sea elephants, royal penguins, and people on Macquarie Island in the 1950s. (State Library of New South Wales. Public domain)
You might have heard of this little Australian island near Antarctica. Attempts to protect its penguins, seabirds, and other rare wildlife and plants from introduced species have been covered by media ranging from the BBC to an Internet comedy site (F-bomb warning for link).
The successes and failures of Macquarie Island predator control programs are also a hot research topic. Even the short story from a literature review is too long for this post (see source list below), so here is the basic outline:
- 1810: Tundra-covered island, rich in wildlife, discovered by Europeans.
- 1818: Cats introduced and do their thing: companionship and pest control.
- 1820: By now, there are also feral cats.
- 1830: House mice are present.
- Late 1870s: Rabbits brought in as a food source; they quickly reproduce and cats switch over to this plentiful prey item.
- 1890s: When ornithologists visit to collect some native birds, people notice that these two bird species are extinct.
- Early 20th century: Ship rats arrive.
- 1950s: People notice that rabbits are overgrazing the vegetation.
- 1960s: Recognition that the overgrazing is having catastrophic effects. Management begins in 1968 by spreading a rabbit flea; it takes a while for that to get established.
- 1978: With rabbit flea now common, a rabbit virus is introduced. The rabbit population begins to shrink after this.
- 1970s: People notice that cats are killing seabirds, and a control program begins.
- 1980s: People notice that cats are switching to seabirds as the rabbits die off. In 1985, a cat eradication program begins and is ramped up in 1998. “The primary knock-down for the eradication used cage trapping and shooting, with most surviving cats captured with leg-hold traps . . . The successful eradication of cats from Macquarie Island [by 2000] . . . provides valuable experience for cat eradication attempts on other large remote islands . . . with minimal use of poisons and provides possible options for sites where broad-scale poisoning, or where aerial distribution of poisons, cannot be used.” (Robinson and Copson, 2013)
- Early 2000s: An estimated pulse of at least 103,000 mice and 36,000 rats enters the Macquarie Island ecosystem after cat eradication. (Bergstrom and others)
- 2006: For technical reasons, the annual distribution of rabbit virus is stopped. After this, rabbit population increases again, with overgrazing of plants and subsequent erosion and other environmental effects.
- 2007: Australia begins an A$24-million project to eradicate rabbits, rats, and mice from Macquarie Island. Success is claimed in 2014.
The most commonly cited reason for the resurgence in Macquarie Island rabbits is the loss of their predators–cats. However, some sources (Springer, 2018) attribute it to less effective virus and the recovery of vegetation.
There is no easy summary for what happened to Macquarie Island’s plant and animal inhabitants after humans got there in the 19th century.
Up until the relatively recent time of environmental awareness, such extinctions and other devastating effects routinely happened–it’s a part of the history of life on Earth. Something similar probably happened in Australia when people and their dogs got there many thousands of years ago.
But today we know much more about what’s going on. Unfortunately, we still don’t understand it all. And human nature being what it is, we very much want to believe that we have corrected our “original error” in bringing invasive species to Macquarie Island, especially after spending millions on it.
But computer modeling of the great Macquarie Island predator eradication programs (Raymond and others) shows that it is possible that mice survived it. If this verifies, that’s bad news.
Experience on Marion Island in the South Atlantic in particular, and in a few other places where all introduced mammals except mice were eradicated, shows that mice will turn carnivorous and go after chicks, thus endangering seabirds all over again.
Obviously conservation and predator control is a much bigger problem than just cat control/eradication, but cat owners and conservationists can help solve it by moving past the emotion toward middle ground. The more people work together, the sooner we will find a good solution for everyone.
There must be a better approach than this:
To achieve success, every single individual of the three pest species [mice, rats, and rabbits on Macquarie Island] must be killed. Anything less is project failure.
— Springer, 2018
Life is going to find a way no matter what we do, so we should tailor our efforts around it instead of focusing on death.
Beginnings are much harder than endings, but they are so worth it!
Featured image: Sponchia at Pixabay. Public domain.
Angel, A.; Wanless, R. M.; and Cooper, J. 2009. Review of impacts of the introduced house mouse on islands in the Southern Ocean: Are mice equivalent to rats?. Biological Invasions, 11(7), 1743-1754.
Bergstrom, D. M.; Lucieer, A.; Kiefer, K.; Wasley, J.; and others. 2009. Indirect effects of invasive species removal devastate World Heritage Island. Journal of Applied Ecology, 46(1), 73-81.
Doherty, T. S., and Ritchie, E. G. 2017. Stop jumping the gun: a call for evidence‐based invasive predator management. Conservation Letters, 10(1), 15-22.
Doherty, T. S.; Glen, A. S.; Nimmo, D. G.; Ritchie, E. G.; and Dickman, C. R. 2016. Invasive predators and global biodiversity loss. Proceedings of the National Academy of Sciences, 113(40), 11261-11265.
Fitzgerald, B. M., and Turner, D. C. 2000. Hunting behaviour of domestic cats and their impact on prey populations, in The Domestic Cat: The Biology of its Behaviour, eds, Turner, D. C., and Bateston, P., 151-175. Cambridge: Cambridge University Press.
Galbreath, R., and Brown, D. 2004. The tale of the lighthouse-keeper’s cat: discovery and extinction of the Stephens Island wren (Traversia lyalli). Notornis. 51(4): 193-200.
Greve, M.; Mathakutha, R.; Steyn, C.; and Chown, S. L. 2017. Terrestrial invasions on sub-Antarctic Marion and Prince Edward Islands. Bothalia-African Biodiversity and Conservation, 47(2): 1-21.
Hall, C. M.; Adams, N. A.; Bradley, J. S.; Bryant, K. A.; and others. 2016. Community attitudes and practices of urban residents regarding predation by pet cats on wildlife: an international comparison. PloS One. 11(4): e0151962.
McDonald, J. L.; Maclean, M.; Evans, M. R.; and Hodgson, D. J. 2015. Reconciling actual and perceived rates of predation by domestic cats. Ecology and Evolution. 5(14): 2745-2753.
Ratcliffe, N.; Bell, M.; Pelembe, T.; Boyle, D.; and others. 2010. The eradication of feral cats from Ascension Island and its subsequent recolonization by seabirds. (Abstract only) Oryx, 44(1), 20-29.
Raymond, B.; McInnes, J.; Dambacher, J. M.; Way, S.; and Bergstrom, D. M. 2011. Qualitative modelling of invasive species eradication on subantarctic Macquarie Island. Journal of Applied Ecology, 48(1), 181-191.
Robertson, S. 2008. A review of feral cat control. Journal of Feline Medicine and Surgery. 10:366-375.
Robinson, S. A., and Copson, G. R. 2014. Eradication of cats (Felis catus) from subantarctic Macquarie Island. (Abstract only) Ecological Management and Restoration, 15(1), 34-40.
Ruscoe, W. A.; Ramsey, D. S.; Pech, R. P.; Sweetapple, P. J.; and others. 2011. Unexpected consequences of control: competitive vs. predator release in a four‐species assemblage of invasive mammals. Ecology Letters, 14(10), 1035-1042.
Springer, K. 2016. Methodology and challenges of a complex multi-species eradication in the sub-Antarctic and immediate effects of invasive species removal. New Zealand Journal of Ecology, 40(2), 273-278.
Springer, K. 2018. Eradication of invasive species on Macquarie Island to restore the natural ecosystem, in Recovering Australian Threatened Species: A Book of Hope, Garnett, S.; Latch, P.; Lindenmeyer, D.; and Woinarski, J. https://books.google.com/books?id=r9FNDwAAQBAJ&printsec=frontcover&source=gbs_atb#v=onepage&q&f=false Last accessed April 9, 2018.
Sunquist, M. and Sunquist, F. 2002. Wild Cats of the World. Chicago and London: University of Chicago Press. Retrieved from https://play.google.com/store/books/details?id=IF8nDwAAQBAJ
Turner, D. C. 2014. Social organisation and behavioural ecology of free-ranging domestic cats, in The Domestic Cat: The Biology of its Behaviour, eds D. C. Turner and P. Bateson, 63-70. Cambridge: Cambridge University Press.