Billions: the domestic cat as scapegoat
A 2013 Telegraph (UK) headline, based on US reporting, reads in part:
…deadly pets murder nearly 4 billion birds a year.
Cats, they mean.
Now, for one thing, murder is an inflammatory word. By the same token, human beings murder thousands of chickens every year…except that we employ low paid workers to do the job for us.
The topic is going through something of a revival, so let’s break it down.
First, we’ll establish that cats should be kept indoors; outdoors only under supervision. We’ll establish that we ought to make public funds available to have all pets spayed and neutered, and that the importance lies in getting someone to do it, not in quibbling over whether that person is poor enough to deserve a “hand-out”; that the production of boutique pets, status pets—all breeding of animals to be used as style points for their owners—should merely stop. And that badly stressed habitats, such as isolated islands, represent particular cases.
Let’s look at a simplified scenario that demonstrates a principle. We’ll create, all at once, a population of 100,000 birds. This species will live for five years. We’ll say, further, that our population is evenly divided between male and female; that each bird pairs with another to breed, and that our 50,000 breeding pairs produce one nestling each spring. For simplicity’s sake the offspring will hold off complicating the numbers by themselves reaching breeding age.
At the end of the first year, we have 150,000 birds. At the end of the fifth year, we have 350,000. All other variables have been excluded. (We can’t—and that’s the point—when using numbers to generate policy, exclude variables to our advantage; yet insist on them to another’s disadvantage.)
And the first generation, having lived the span of its years, dies before the sixth, thus reducing the population by 100,000. We have increased our original population by two and a half times.
Now we need to bring real life into the picture. Burgeoning as they are, our birds will soon run out of food and nesting sites. Insufficiencies of those are two of the stresses that, in nature, control excess population.
Others are accidental death, disease, loss of habitat, predation, and senescence.
The fact of predation, then, is not by itself deplorable. If this or any other stress destroys generation after generation of newly-hatched offspring, or prevents the parent birds from nesting, numbers may decrease to the point they can’t be replenished; however, this is likeliest to occur where conditions favor the survival of predators, while limiting a prey species’ ability to rebound. All species maximize their survival to the extent they can; they do not purposely choose an ecosystem of which only a single example remains. The Carolina parakeet, we may consider, once was hunted for its feathers (or killed for feeding on orchard fruits), to extinction—its predators being uniquely adapted, by their powers of invention, to spread into every ecosystem on earth, and thrive.
Let’s look at a second scenario. We have a population of birds, divided into five species, 100 of each, 500 total. These are: Wood stork, Clark’s Nutcracker, Red-winged blackbird, Mourning dove, Cardinal. We have a specimen of Felis catus, Jerry by name. Jerry the tabby has been monitored, on behalf of a surveying group, by the woman who feeds him. Her report generates a calculation, that Jerry will kill 100 birds in a year. He will kill, therefore, by estimate, one-fifth—20%—of our bird population.
The Wood stork, however—once again to introduce real-life variables—lives and breeds in the Gulf coast wetlands. The Clark’s Nutcracker lives and breeds in the mountains of America’s western states. Jerry, as a representative feral cat, is less likely to live in either environment, than in a city or suburb, close to human beings, the hiding places they make, and the trash they generate. Suppose Jerry kills zero Wood storks; zero Nutcrackers. Our 100 is an extrapolated number. We can believe the number is good, and that Jerry must therefore kill somewhat nearer a third of the three remaining species. We can say that if we’ve assigned “twenty killed” to each species, and our monitoring seems to confirm it, while our knowledge of habitat conditions seems to deny it, we’ll just change our estimate. We can say he really kills sixty birds.
Do house cats who are not being fed by humans ever form colonies? Do feral cats live in any numbers in places that are truly wild—boreal forest, desert, wetland? Would a cat in a national forest displace other predators, bringing the number of kills back to its level, or would the cat’s predations be added to the total taken by foxes, owls, eagles, hawks, snakes, weasels, pumas, coyotes, wolves, bears?
Perhaps we ought not to speak of predation in terms of all birds, but say, rather—realistically enough—that Jerry kills the birds he can get, and that the birds he can get are readily available for study; that if we would like to determine how their numbers fluctuate from year to year, which episodes of decline can be attributed to West Nile virus, glass windows, or loss of habitat, in addition to predation, we can get better science by plugging cats in with other stresses; by factoring, on the opposing side, increased feeding and nesting opportunities which may lead—if we will set aside wild land and protect it—to a slump in population being followed by a boom.
If we determine how many ranges of bird habitat exist that have no significant overlap with (significant) feral cat populations, we can use real information to counter instances of two things being placed side by side, and readers being expected to conclude from this, cause and effect.
2017, Stephanie Foster