I came across this gem of an article on my facebook, and I couldn’t handle it. This is unintentional science denial at its worst. I’ve responded briefly to each of the 5 claims made by the author.
“5 Ways Feral Cats Do More Good Than Harm for Wildlife”
- They kill other animals that cause harm
On Australian islands where feral cats were eliminated, rat populations rose exponentially. Rats are notorious for eating bird eggs, and as a result of being overrun by rats, bird populations on those islands were decimated.
Okay, this situation isn’t evidence that cats are good. Cats were removed from Macquarie Island because they were negatively affecting the native bird population. The implication here was not that cats were preventing bird deaths and environmental damage, but that they are the lesser of two evils.
- They kill the weakest and slowest animals
By eating rodents or birds that don’t have the health and vitality to survive, or that lack the ability to camouflage themselves, feral cats help to assure that prey animal populations become stronger and more adapted to their environment.
This style of predation occurs in ecosystems where predator and prey species have been co-evolving. When cats are introduced to ecosystems where none of the prey species have co-evolved with them, the cats are able to capture and kill healthy, smart, and young animals too.
The best example for this I can think of is bat predation by feral cats. I was attending the 2009 Animal Behavior Society Annual Meeting, and a graduate student was scheduled to give a talk on feral cat predation of bats. During her presentation she presented a video of a feral cat standing at a cave entrance nabbing bats as they came out. These weren’t weak, old, or stupid bats… They were healthy robust flyers out for their nightly feed. The point is that cats are such astounding predators that they can decimate individual populations of native animals before natural selection has time to kick in and create adaptive responses that mitigate predation by cats. More about cats and bats here.
- They make prey animals smarter
Prey animals that learn that cats are to be avoided teach this lesson to their offspring. Those that get the clue will survive, and therefore the population as a whole will become smarter and more likely to live to reproduce.
Natural selection pressure for predator avoidance is not the same as natural selection for general intelligence. Small mammals that are adapted avoid cats aren’t smarter in general, they just avoid cats, but that doesn’t even matter. Please see my previous point that many populations of animals under siege by feral cats do not have time for natural selection to act on their predatory avoidance behavior before being snuffed out.
- They help to maintain the ecosystem
If prey populations rise too high, the impacts on the environment can be profound. After the elimination of feral cats in Australia’s Macquarie Island, rabbit populations exploded and rabbit grazing destroyed albatross habitats. By preying on those rabbits, feral cats helped to ensure that the island’s ecosystem remained stable.
The ecosystem was not stable with cats, sea bird populations were declining due to predation by cats.
- They increase biodiversity
Because predators are more likely to kill animals that have a higher population, they make room for other animals that fill the same ecological niche. Shrews and birds both eat worms, for example, but if the shrew population rises high enough to threaten the birds’ ability to eat, feral cats will come to the rescue: they’re much more likely to eat shrews since there are so many more of them, therefore leaving more food for the birds.
It is widely accepted in the scientific community that feral cats, when introduced to new ecosystems, decrease biodiversity. Point #5 is simply fantasy. Read more about cats and island biodiversity here.
As for the hypothetical example of cats benefiting birds by keep shrews in check…
What happens when cats have access to an overabundance of shrews to eat? In this example, there are so many shrews that they are decimating worm populations, so it’s implied there are a metric S!&$-ton of shrews. What happens to predator populations when there is an overabundance of prey? Their population increases. What happens to the birds in this example when they cat population explodes in response to shrew overpopulation? Now that there are more predators in the ecosystem than the shrew population can sustain, the cats will start eating birds. This competition between birds and shrews is called apparent competition, and it’s been widely studied. Learn more about it here.
Long story short, please keep your pet cat inside and consider supporting well planned feral cat removal instead of Capture/Neuter/Release programs. It’s safer for your pet cat, and your local wildlife population thanks you.