Cat
The domestic cat's ecological impact presents something of a controversial ledger. On the asset side, cats provide rodent control services valued in agricultural and urban contexts since ancient Egypt. On the liability side, cats are responsible for an estimated 1.3 to 4 billion bird deaths annually in the United States alone, contributing to population declines in numerous species. Cats occupy the peculiar position of being simultaneously beloved companions and significant ecological disruptors—a tension their owners largely prefer not to examine too closely.
Bat
Bat ecological contribution operates almost entirely in the positive column. Insectivorous bats consume vast quantities of agricultural pests, providing pest control services valued at billions of dollars annually. Fruit bats serve as essential pollinators and seed dispersers for hundreds of plant species, including economically crucial crops. Bat guano functions as premium fertiliser. Even vampire bats contribute anticoagulant compounds useful in medical research. The bat, unlike the cat, can claim an almost unblemished record of ecological beneficence.