Prensis / Getty ImagesBirds can also suffer stress when chased by dogs, which have a natural prey drivePrensis / Getty Images
Despite being domesticated and occasionally pampered, pet dogs and cats—which number around one billion and 500 million, respectively—have not stopped being predators. When allowed to roam off-leash and without their owners, they can cause serious damage to other species. According to a study by Curtin University, Australia, cats are the prime suspects in the deaths of 500 brown kiwis (New Zealand’s national bird) in a colony of 900 and the falling number of penguins in Tasmania. They also kill chicks nesting on beaches, including endangered birds, such as the hooded plover. Even on a leash, dogs can injure, frighten, or kill reptiles and birds. In the USA, deer will run for longer from a person with a dog on a leash than from a person alone. Furthermore, their feces and urine can transfer zoonoses to wildlife and pollute waterways (Pacific Conservation Biology, April 10).
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