Before the arrival of man, marine mammals were the only mammalian predators of penguins in New Zealand. Rats were the first mammalian predators introduced, albeit accidentally, but several more were deliberately introduced. Cats were the first, in an effort to control rats and mice. There is now a large population of wild cats in New Zealand, which is continually added to by the dumping of unwanted kittens by irresponsible pet owners
Ferrets (the domesticated version of the European polecat), stoats and weasels (all part of the mustelid family) were introduced the North and South Islands in the 1880's in a bid to control an exploding rabbit population (another short-sighted European introduction). There was vocal opposition to the introduction of mustelids from a number of eminent naturalists, but the farming lobby won the day - to the detriment of New Zealand's wildlife.
Ferrets, stoats and cats have all proved to be efficient predators of penguins. Blue penguins are particularly vulnerable to the mustelids, and a single ferret may kill a dozen birds in one night. Larger penguins, like the yellow-eyed, are less vulnerable as adults, but their chicks are extremely vulnerable to predation. The trapping of predators occurs in many mainland yellow-eyed penguin colonies to ensure the survival of chicks, but many areas where other penguin species live are too inaccessable to control predators.
Mans best friend
Domestic dogs can also be penguin predators. Adult penguins are at the most risk as they cross beaches and open areas to get to their nests or as they incubate eggs or chicks. Dogs are banned from publicly-owned penguin reserves, but some dog owners chose to ignore "no dogs" signs. In 2001, two dogs were responsible for the deaths of 72 blue penguins in a wildlife reserve in Oamaru.
The threat from above
The only significant aerial predators are the skua (a large gull-like bird) and the giant petrel. Both species are common around Antarctic and sub-antarctic penguin colonies and small numbers are found on Stewart and Chatham islands. Blue penguins are the only species that Skuas regularly kill, however they will quickly take poorly guarded eggs and chicks from any penguin species
The threat from below
Sharks, seals, sealions and, occasionally, orca are all marine predators of penguins. Leopard seals, usually residents of the Antarctic region, are specialist penguin predators and are occasionally seen as far north as the North Island. NZ sealions occasionally dine on penguins, but fur seals rarely do so. Sharks kill an unknown of mainly young penguins but also inflict injureies on others. Also regularly inflicting injuries on yellow-eyed and crested penguins are barracouta who bite at the feet of the penguins, causing injuries that in themselves are not fatal but then often become infected.
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