Cats: our feline friends, or are they?

(Cat eating a bird it has just killed.)

About a decade ago I had a student in my Conservation Biology class named Scott Boomer. We were discussing the problem of non-native organisms that week, and Scott told me he had kept some interesting records on the behavior of three cats that he and his wife had at that time. The cats (one male, two females, and all neutered) had access to food and water in Scott’s apartment around the clock. The three natural predators had the habit of capturing prey outside and bringing it back to Scott, often dropping it at his feet or putting it in their bathtub. Scott is a biologist and he was able to identify all the prey items returned to his apartment over a 2-year period.

The list included:

Mammals: 5 deer mice, 2 woodland jumping mice, 5 Eastern chipmunks, 4 meadow voles, 1 gray squirrel, 6 star-nosed moles, 4 short-tailed shrews, 1 cinereus shrew, 2 little brown bats, 1 Eastern cottontail

Amphibians: 2 green frogs

Reptiles: 1 Eastern painted turtle, 3 Eastern garter snakes

Birds: 3 common yellowthroats, 2 black-capped chickadees, 1 house wren

Total: 43 animals

Now, there are about 90 million cats in the U.S., according to the 2005-2006 National Pet Owners Survey. A certain percentage of those cats never go outside. But anyway you run the numbers, the collective mortality on native wildlife by U.S. cats must total millions of individuals of dozens of species. In some places in the world, feral cats, those that have gone completely wild, are responsible for the demise of rare species of birds. The Stephens Island wren (a flightless species) in New Zealand went extinct in the late 1800’s due to the island’s cats, or so that story goes. The wedge-tailed shearwater in Hawaii is also impacted by cats. Conservation biologists actively control cats (as well as non-native rats, mongoose, etc.) in such places today, especially on oceanic islands.

We hear a lot these days about our “ecological footprint”, or the impact that a human has on the earth’s natural resources and ecosystems. I doubt that our pet ownership is included in these calculations. Remember that I tend to think in terms of quantity and quality of habitat for biodiversity. I usually think of our “habitat footprint” as defined by the boundaries of our house and the lawn surrounding it. But the effect of that living space penetrates further depending on the chemicals we use on the property, how far away we or our children trounce on the environment, and the influence of our pets, of which cats are probably the worst offenders. There are zones of concentric circles beginning with the epicenter of the house itself, which include areas of decreasing influence on the fauna and flora that is there now, as one moves respectively outward. Cats probably have an effect in each of those zones, but they may represent the only threat in the outermost circle, which is perhaps several hundred meters from the edge of the house.

In fact, last year someone built a new house about 100 meters from the edge of my woodlot. For the past few months, I have had two cats roaming my property that I am sure live at that house. I have not had cats on my property in 20 years. And so it goes. We increase our collective ecological footprint, we chip away at the quantity and quality of wildlife habitat and, in my opinion, the quality of life is diminished just a little bit more---again.

In these few paragraphs I wanted to increase your awareness of an idea that perhaps you have not thought much about--- how that lovable pet cat of yours is possibly reducing the biological diversity in your neighborhood. I do not intend to explore a detailed solution to this problem, although attaching a simple bell to your outdoor cat would probably reduce its kill rate. You might be thinking that cats kill organisms that people do not like very much anyway, so what the heck. But I can assure you that every one of those species killed by Scott’s cats represents a unique and interesting biological story. Remember that not so long ago, nearly everyone thought it was fine to shoot, trap, or poison wolves, mountain lions, and eagles.

The toad who loved traps

(Guess who came to dinner?)

Every summer I have an American toad (Bufo americanus) that usually spends some time in my garage. Insects accumulate in one corner, and I suppose this becomes a sort of toad luncheonette. For a few days in early July, I found an adult toad sitting during the day behind the open door to the garage. I assume it went outside to forage at night, when toads are most active, but I never really followed him at that time.

Completely separate from anything to do with the toad, we have always had a deer mouse (Peromyscus sp.) problem at our house. Deer mice regularly enter the house somewhere, and they end up under the kitchen sink. So, for years I have kept metal box traps, known as Sherman live traps, set in the kitchen and along a raised wall in the garage. The garage is my first line of defense, where I capture many mice before they even break into the house. This trap has a spring-loaded door, so that once an animal enters the trap, it steps on a treadle on the floor of the trap, which causes the door to snap shut, trapping the animal inside. It is a valuable tool used by biologists who study small mammals. (By the way, deer mice love dark cavernous places, so I never even bait these traps with food. Just open the trap door, set it in a likely runway, and it functions like a deer mouse magnet).

So in July, when I noticed that the trap in the garage was closed, I assumed I had another deer mouse to release far from the house in the woods. But when I opened the trap, a large American toad was inside. I released the toad on the floor of the garage, reset the trap, and had a good laugh about it with my wife. But to my amazement, the next day, the same toad was in the closed trap again. This time, I took the photo you see above, and released the habitual prisoner again. I never saw that toad after that second capture.

Now, this toad’s behavior is somewhat endearing, and it reminded me immediately of the “Frog and Toad” series of children’s books by Arnold Lobel, which I have read to my children and grandchildren many times. But the most interesting part of this anecdote is yet to come. Notice in the photo above where this trap was located. It is on a ledge about two feet above the floor of the garage, much higher than toads can jump. But also notice the lumber, stacked in stair-step fashion adjacent to this wall. The only way this toad could have reached the ledge is to have hopped up each level of lumber to get to that ledge and the trap. And, it performed that maneuver two nights in a row.

Why did this toad go to so much trouble to get to that ledge, and then enter that metal box? To get to the other side? To explore worlds unknown to other toads? To get featured in a DrTom blog? I have no idea. But it proves how entertaining nature can be, even in your very own garage.