They offer a few studies that show different results, but the overwhelming scientific evidence points to free roaming cats as successful predators. Even websites that support feral cats praise their hunting ability. During the 'pounce,' she has already determined where the mouse will be, and is able to land on top or very close to it, and reaching down, bites the mouse at the top of the neck. Alley Cat Allies, an organization that supports TNR projects across the country, states in its literature that the impact free roaming cats have on bird populations is insignificant. But research findings they publish note that birds make up 20 percent of the diet of free-roaming cats.
Cats are exotic predators.
They have been in the states only a few hundred years. Not only do they feed on native species, they compete with native predators for the same food source. To subsidize these predators, as is the case with managed colonies, increases the advantage they have over natural predators and maintains densities unheard of in natural predator-prey relationships. It is a totally unnatural situation. TNR needs to be studied in controlled situations to determine its effectiveness.