My renters abandoned their house in the middle of the summer a couple of years ago. I was upset, but not about losing money. My renters were house wrens, and they leased the one-bedroom home for a song.
I was more worried, just as they were, that the neighborhood had grown too dangerous. Two cats from next door claimed my backyard as their territory. That summer, the cats laid in wait for the wrens as they gathered twigs, grass and other tidbits for their nest.
The wrens kept their eyes on the cats and carefully chose nesting material from open areas where they felt safe. But when their first brood began to fledge, the real problem began. Whenever I was home and heard the parents' distinctive danger calls, I chased the cats from the young birds. Normally the wrens raised several broods in my backyard each summer. But that year, after one nesting, they headed for safer, cat-free ground.
A quick count revealed nine outdoor cats lived within a radius of three houses from mine. All the owners but one ignored the frantic cries of distraught birds trying to protect their young. "It's just part of nature," most replied.
Domesticated cats, however, have advantages over native predators that go after the same food. In a study on rural free-ranging cats, John S. Coleman and Stanley A. Temple of the University of Wisconsin in Madison, found "up to 114 cats per square mile, which is several times higher than the combined densities of all similar-sized native predators, such as foxes, skunks, opossums and raccoons."
In urban areas, the numbers can be even more alarming, especially in cities with large populations of feral cats. With a higher than normal number of predators, the bird population often suffers.
Large populations of cats are able to exist because of several reasons, according to researchers Coleman, Temple and Scott R. Craven. People feed cats, so their survival isn't dependent upon the amount of prey they find. Pet owners also protect them from disease and predation, factors that help control the number of other predators. Combine these advantages with a cat's ancestral drive to hunt, and the odds turn sharply against the birds.
Domesticated house cats most likely descended from the African wild cat. As northern Africans turned from hunting and gathering to agriculture around 5000 B.C., they encouraged these tabby-colored wild cats to live around their grain storage bins to eat rats and mice. Over time the cats became domesticated, at least as much as a cat can be tamed.
Domesticated cats arrived in the New World on the Mayflower. In the mid 1700s, large numbers of cats were imported to rid the colonies of an abundance of black rats that was causing disease and eating grain. Today cats are still kept for their mousing ability, especially in rural areas, but their big draw is as companions--gentle souls with whom to share one's home and life.
Because they are so independent, cats are a perfect pet for busy people. As a result, the number of cats kept as pets has grown rapidly, surpassing the number of dogs in the 1980s. U.S. Census records from 1990 show that 60 million cats are kept as pets, up from 50 million in 1980. Millions more are feral. Coleman, Temple and Craven estimate that the combined number of pet and free-ranging cats in the United States is more than 100 million.
Despite 7,000 years of living among people, the kitten that sits on your window sill carries traits similar to its wild relatives. That fuzzy, affectionate, yet aloof, ball of fur sharing your home is one of the most efficient hunters in the animal kingdom. A muscular build is a key to their success.
More than 500 muscles give cats the bursts of power they need to pounce upon their prey. Strong muscles in the lower back, hind legs, neck and shoulders help cats leap up to five times their own height. Muscles, along with ligaments, hold the spinal column together, allowing the cat to move with great flexibility. The shoulder joint, too, is flexible, which helps the cat grab divebombing birds that are protecting nests and fledglings.
Muscles help with their keen sense of hearing. Using the more than 25 muscles in its ears, cats can quickly turn each ear individually 180 degrees in any direction to pinpoint the exact location of prey. Their ears are so sensitive, they can hear a mouse walk across a floor.
Other senses, like sight and touch, also aid their hunting ability. Cats can't see in complete darkness, but it may seem that way. Because of the curvature of their cornea, cats need one-sixth as much light to see as people do. As a result, cats can see movement and objects at dusk and dawn. In the dead of night, with no available light, cats can still locate prey with their sense of touch. Special nerve endings at the base of their whiskers allow cats to feel slight changes in air currents caused by a mouse walking back to its nest or a thrush stirring silently in a bush at night.
It's easy to tell when a cat is ready to spring into action. For instance, when it spots a junco feeding on the ground near a feeder, it flicks its tail, flattens its ears and quietly moves forward. When in range, it stops, curls its back, then leaps next to the bird. The back paws touch the ground beside the junco, so the cat can quickly sink its teeth and claws into the bird.
Many cat owners do not witness this deadly ballet. Instead, they see only about half the birds that cats kill, according to several studies. To discover the effects of house cats on birds and other small mammals, Peter B. Churcher and John H. Lawton studied 78 cats that lived in a small Bedfordshire village in England.
For a year, all the cat owners but one collected the remains of animals their cats had killed. When possible, they also noted catches they witnessed where no remains were left. The researchers discovered that 35 percent of the annual total was birds. The percentage rose during the winter when small mammals weren't as active.
Sixteen percent of all kills were house sparrows. By studying the number of sparrows in the area and comparing it to the number the cats brought home, the researchers concluded that between a third and a half of all sparrow deaths were caused by cats. They also discovered that cats that lived in the interior of the village killed more birds than those that lived near fields.
In conclusion, Churcher and Lawton then multiplied the mean annual catch of the village cats by the estimated total of domestic cats in Britain. The result was 70 million kills, of which between 30 to 50 percent may be birds. They concluded that cats in England kill at least 20 million birds each year.
In the United States, Craven, Coleman and Temple estimate that rural cats alone kill more than a billion small mammals and hundreds of millions of birds each year. Urban and suburban cats--especially if they have limited access to rodents--cause the estimate to go higher.
Cats, of course, aren't the only threat to birds. Combine the cat's impact with the destruction of habitat and the use of pesticides and the birds are big losers. In towns, competition from exotic birds, like English sparrows and starlings, for nesting cavities keeps many native species from finding safe places to raise young, says Jane Fitzgerald, Midwest coordinator for Partners in Flight, an organization dedicated to the conservation of birds. "The biggest threat is in the country," Fitzgerald says, "where cats have the potential to disrupt more natural ecosystems."
Back in my urban neighborhood, the battle continues. This year wrens returned to my backyard after the two cats from next door moved away. The backyard is cat free once again, but the front yard isn't as safe for another wren family in the ash tree and the cardinals nesting in the lilac bush next to the front porch. A new cat moved in across the street, and as I was writing this story, I saw it pounce on the male cardinal. A quick yell from me at the moment of capture caught the cat off guard, and the bird flew free.
It's possible to enjoy the company of cats without having to forego the sight of robins plucking worms from freshly tilled soil, the sounds of mourning doves gently announcing the morning with their cooing or the satisfaction of knowing that hungry wrens are eating the insects that would otherwise bug gardeners and gardens.
The best solution is to keep cats indoors. Dr. Jack Horton of Columbia, Mo., a recently retired veterinarian who specialized in felines and other small animals for 40 years, says keeping cats indoors prolongs cats' lives and protects wild bird populations.
Cats kept indoors live longer, he says, because they are exposed to fewer diseases, such as rabies, feline distemper and leukemia, they don't suffer wounds and resultant infections during territorial battles with other cats, and they are not run over by cars, a major cause of feline death.
Tips on protecting birds from outdoor cats
Because some cat owners do allow their cats outdoors, birdwatchers must take precautions for the birds' sake. Here are a few that are recommended by bird experts and researchers across the country.
It's hard for many people to believe that the gentle cat curled up on their bed at night can be one of the most efficient killers in nature. According to studies, the following beliefs about cats are not true.
A healthy well-fed cat is a more efficient hunter than a hungry feral one because cats hunt even when they aren't hungry.
They may not have razor-sharp claws to grab hold of the prey, but a clawless cat can use its agile front legs to deliver a stunning blow with its foot and its sharp teeth to bite into the prey's neck.
Kittens are born with the instinct to hunt. However, they often become more efficient hunters if the mother shows them how.
Cats sleep two-thirds of the day but they are always on alert. Cats rest a lot because they are not designed for endurance. They use high levels of energy for short periods, then rest to recover. Even when they appear to be snoozing, they are light sleepers and alert to sounds and movement around them.
This may be true in rural areas, where studies show that birds make up 20 percent of a cat's diet. But cats are opportunists, and in urban areas where rodent populations are kept down by other means, birds may be the most readily available prey.
Throughout time, people have put bells on cats to keep them from catching birds, but it represents a false sense of security, according to Dr. Horton. Many times birds know exactly where the predator is. Distraught birds will dive bomb a cat to get it to move away from their young. The cat's agile front legs allow it to easily reach up and grab the bird.
When a belled cat sneaks up on a bird, the clapper in the bell usually doesn't ring until the final pounce, when it's often too late for the bird to respond. Instead of being a warning, the bell around a cat's neck may be a death knell for the unsuspecting bird.
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