Bird conservationists are perhaps the most effective opponents of Trap-Neuter-Return (TNR) programs for feral cats. The conservationists argue that scientific studies show that cats kill huge numbers of birds, and that therefore cats must be removed from the environment to protect birds. TNR supporters argue that estimates of cat predation are overblown and, in any event, TNR is the only successful way to manage cat populations. Although most of the bird conservationists won’t come right out and say it, what they all seem to want is to round up and kill all homeless and feral cats and to force people who own pet cats to confine them indoors. Current estimates are that there are at least 80 million pet cats and tens of millions of feral cats in the United States.
Recently I began studying the science of the cat-predation issue. Because the science is controversial I expected to find what I usually see in scientific controversies, which is evidence on both sides of the issue. What I actually found ran completely counter to my expectations, and shocked me. In journal article after journal article, and book after book, I found cat-predation studies that were flawed by small sample size, samples that were not shown to be typical, unjustified generalizations, a failure to account for confounding factors, and a tendency to assume that predation of individual birds necessarily resulted in damage to bird populations at the species level.
After perusing the studies and writings of many bird conservationists I came to the conclusion that they were unable to see the data clearly. As someone who is a great believer in the scientific method, and who respects scientists, I don’t say this lightly. I’m used to scientists being the people we can rely on to look at issues dispassionately and give us objective conclusions based on data. I had always assumed that there must be some “there” there in the cat-predation controversy, simply because there are reputable scientists who strongly believe that cats harm bird populations. So it was a very rude awakening when I began to study the data and saw how unconvincing the evidence against cats in general, and TNR in particular, actually was.
I don’t have the space in this blog post to dissect the weaknesses of all the scientific studies, and others have done that anyway (see Peter Wolf’s “Vox Felina” blog, linked in the left sidebar). The point that I want to make here is somewhat different, and that is that the bird conservationists, regardless of the validity or lack of validity in the studies they publish in journals, exhibit contradictions in their own writings about cats that are clear evidence of their lack of objectivity on this issue. As a case in point, we need only look at John M. Marzluff’s book “Welcome to Subirdia.” Marzluff is a respected professor of Wildlife Science at the University of Washington. I thought “Welcome to Subirdia” was a delightful and important book, and I would recommend it to anyone. The thesis of the book is that green suburbs are unexpectedly wonderful habitat for birds, and nurture a wide variety of bird species.
But in spite of Marzluff’s happy message of birds doing extremely well in the suburbs, his book is marred with inexplicable internal contradictions when he talks about cats. To start with, we know that there are probably as many free-roaming cats in the suburbs as there are anyplace on earth, except possibly for some neglected urban areas. Given this, how would you complete the following syllogism:
In the suburbs we find an abundance of bird species, cats are also abundant in the suburbs, so —
Choice A: cats do not harm and may even help bird species, or
Choice B: we need to confine or kill all the cats in order to save the birds.
It seems to me that any rational scientist would pick “A” to complete the syllogism, but Marzluff pretty clearly agrees with “B.” In fact, on page 85 of the book he says that cat predation on birds is “horrifying.” On page 173 he says that the “most uniformly serious” peril to birds and other animals in the city is the free-roaming domestic cat.
But wait, Dr. Marzluff, wait! Didn’t you just explain to us in a very well-written and convincing way that green suburbs are among the best habitats for birds? Didn’t you tell us on pages 15-16 that you found more bird diversity in Central Park in New York City than you did in Yellowstone? And aren’t there a whole lot more domestic cats in the suburbs than in Yellowstone?– my head is hurting.
There’s more. One of Marzluff’s students did an experiment to examine causes of mortality of fledgling birds (pages 91-93). Unlike many bird-mortality studies, this one seems to have been designed and carried out fairly well. It was perhaps a bit small, with a sample size of 122 fledglings, but that number is large enough to be at least indicative, although not conclusive. The best thing about the study design was that the birds were radio-tracked. This allowed Marzluff and his student to determine the location and movements of the fledglings for the approximately three to nine weeks that the batteries lasted. The period of a few days when a bird is learning to fly is one of the most vulnerable time periods of its life. If cats really do account for 10% of deaths of all birds in the United States (as Marzluff maintains, see pages 85 and 188) then we would expect cats to kill a substantially higher percentage of fledglings – 20%, 30%, perhaps even upwards of 50%.
The results were extremely interesting. What the study actually showed was that cats were “implicated” in the death of only one fledgling. And Marzluff admits that it was not clear that the one fledgling was actually killed by a cat, and it could have been killed by another mammal or even another bird. Now, one would think that a good scientist like Marzluff, on receiving this data from an experiment that he and his student performed themselves, might scratch his head and say — maybe cats really aren’t as bad as we thought. Or at least — this is interesting, we need to study this in more depth. But that isn’t what Marzluff said. Instead, he dismissed the “rarity” of cat predation in the study (by which I think he means the “non-existence” or “near non-existence” of cat predation in the study) by opining that it was due to the presence of coyotes in the area.
If coyotes were prevalent enough in the area of the study to chase away or kill off all the cats, then one would think that coyotes would have killed some of those fledglings themselves. Perhaps they did. But Marzluff believes that coyote predation is good for bird populations (page 199). According to Marzluff, cats kill birds (bad), but coyotes “cull” their prey, which is good because it is nature’s way and they only kill the injured, weak and overly abundant. Predator coyotes are wonderful, while the slightly smaller predator cat is horrible. Okay, now my head is going to explode.
I really don’t mean to pick on Marzluff. Others are worse than him. I’m discussing “Welcome to Subirdia” in this blog post because it happens to offer a particularly clear example of the way the cat issue seems to twist the thinking of even good scientists. So, back to the question – why does this happen? Why are bird conservationists, who make their careers by being logical and fair and sticking to the data, seemingly so blinded by their anti-cat emotions that they cannot see the data clearly?
If I were going to study the issue I would start with two hypotheses. One is the hypothesis that bird conservationists have an animus toward cats because they view cats as an “invasive” species. As I discussed in a blog post last month, there is recent thinking that the whole “invasive species” thing is really just mother nature’s reaction to the massive changes that humans have made in the environment. My second hypothesis is that there is a prejudice against cats due to the perception that they are cruel killers because they sometimes seem to torment their prey or play with it before killing it. Scientists ought to know, if anyone does, that species do not survive and thrive the way cats have if they waste energy. Therefore, there is probably a reason for the way cats sometimes make their kills. One obvious reason would be that they are learning or improving hunting skills. Cats are not very big, and in some habitats they need to kill prey animals, such as rats, that are almost as big as they are. A cat does not have the luxury of the size and weight of a coyote or wolf. Since cats cannot always overpower their prey by brute force, they have to fight with skill and tactics – which takes practice.
Whatever the reason or reasons for the animus that bird conservationists have toward cats, it has consequences. We need look no further than Washington, DC, where a battle is now being waged between TNR advocates and conservationists who want to round up cats and take them to shelters (where the feral ones would be killed) and force owners of pet cats to keep them indoors on pain of death (death to the cats, not the owners, although sometimes one wonders).
This is already a long blog post and I don’t have space here to get very deeply into the related question of why bird conservationists reject TNR. There is one glaring logical contradiction here, too, though, that I want to touch on. Even if we all were to agree that cats are damaging bird populations at the species level (an idea that Welcome to Subirdia very neatly refutes), one would think that bird conservationists and cat advocates could nevertheless agree on TNR, because TNR not only reduces the number of cats, it also reduces the need of cats to hunt, since colony caregivers feed the cats. Moreover, probably 99% of the labor and supplies that are expended on TNR and colony care are donated by volunteers, without costing taxpayers or businesses a dime. Catch-and-kill methods have to be repeated every two years at least, they are expensive, and the advocates of the catch-and-kill method have not figured out how to keep people from sabotaging it by very naturally doing everything they can short of going to jail to save their neighborhood cats.
The bird-conservationist ranks do not seem to contain enough people who are willing to catch and kill cats all over the country with volunteer labor and supplies, so the bird conservationists expect governments to pick up the tab for their cat-killing program. This adds insult to injury, because it means that citizens who pay taxes are forced to pay for killing cats, when in fact the majority do not approve of the wholesale slaughter of cats. This is not a winning scenario for the conservationists. It can only lead to long, drawn-out, pitched battles that the conservationists will ultimately lose, because they are not only in the wrong, they are in the minority. One would think that the bird conservationists would realize that TNR is the best solution that is actually possible to achieve, even if it is not their favorite solution. Instead, they continue to oppose TNR, holding out for the unrealistic option of somehow finding, catching and killing every cat that wanders outdoors, and forcing people who disagree with them to pay for it.
We can’t send all the bird conservationists back to science school, so all we can do is hope that eventually rationality will prevail. In the meantime, pick up a copy of Welcome to Subirdia. I’m sure you’ll love it. It’s a very convincing argument that birds do better with cats around.
留言