April 2008

The Conservation Committee of Tucson Audubon recently recommended that the Board adopt a policy on feral and free-range cats, and the Board did so at its February meeting. I helped develop the policy and voted for it both at the committee and board level. That policy is set out in this issue of the Vermilion Flycatcher (see page 17).While I endorse the policy, I feel uneasy about it because I do not think we are analyzing the problem in a dispassionate scientific manner. Before I set out my hypothesis let me reveal two facts. One is that I am a long-time cat owner, and the other is that the last course that I took in biology was in high school, nearly 60 years ago. Therefore, there may be some built-in cat bias, and my biological arguments may be simplistic or even flawed; but I feel compelled to state them anyway. I should also point out that I am discussing feral cats that congregate in colonies in urban areas. Feral cats in rural or suburban areas do not seem to establish colonies, for reasons I will point out later.

There is no question that feral cats kill millions of birds. It is also reasonable to expect that if feral cat populations were reduced or eliminated the bird populations in those habitats would increase. We should remember, however, that these birds are not living in their natural environments. They are living in habitats that have been fragmented and degraded and are completely different from the environments that existed when they evolved. We love birds and we want to protect them; however, we are the prime cause of their decline. Do our attempts to protect the birds living in these fractured environments make up for the loss of their habitats? Even if protecting birds from feral cats increases their numbers, is this in the best longterm interest of the species?

Let us consider how birds lived before their habitats were destroyed. Like all other animals, birds are subject to natural selection. One of the central features of natural selection is fitness. The strong live longer and breed over a longer period and the weak and injured perish younger. Birds that are better able to avoid being killed and eaten by predators live longer, breed longer, and pass on that trait. Birds that are not subject to predators, such as those that populated the Hawaiian and Galapagos Islands, lost that ability because they were predator-free for long periods. That is not the case here. In the Sonoran Desert, some of the animals that preyed on birds, before their habitats were destroyed are: bobcats, jaguarundi, ocelot, margay, gray wolves, coyotes, gray fox, kit fox, Mexican raccoons, coatis, ringtails, badger, black-footed ferrets, several types of skunks, a wide variety of snakes, gila monsters, and other birds such as hawks, owls and shrikes. How many of these predators are living today in the fractured habitats we have created?

Accordingly, birds evolved with many natural predators, and then we destroyed much of their habitat, but also eliminated most of their predators. The elimination of these predators probably also enabled feral cat populations to get out of control because many of the predators of birds would also be the predators of cats. Could it be that feral cats are, in some imperfect way, substitutes for the predators that have been eliminated? If this were a valid hypothesis, it would be important to know what species of birds are being killed by feral cats, and the age and condition of the birds when they were killed. In addition, it might be important to study what happens to birds that breed in areas where their predators were eliminated, when they migrate to their wintering grounds where predators continue to exist.

Yes, feral cats are an invasive species, but they are no better hunters of birds than bobcats, ocelots, and the other native, but no longer present, cat species. The primary diet of feral cats is not birds, but small mammals, amphibians and reptiles. If the feral cat populations were eliminated, an unintended consequence might be an increase in rodent populations, because most of the other small mammal predators are no longer present.We should also remember that rodents are also bird predators. There are even recent studies that have shown that when rodents and feral cats are preying on birds, the elimination of the cats alone causes an even greater decline in the bird populations.

In conclusion, I reiterate my endorsement of Tucson Audubon’s policy on feral and free-ranging cats, but I believe that we can only reduce feral cat populations and will never completely eliminate them. Feral cats are a permanent part of our environment, so we must learn at what levels they can be tolerated. Any study must take into consideration more than the effect that one animal has on another animal, because the natural environment is complex, and any changes can have multiple consequences.

Contact Herb at herb@trossman.net or 749-5825