There are 41 species of mammals which are found in the American state of Hawaii.^[1] Of these, 24 are native, while the other 17 are invasive. Because Hawaii is so far from other land masses, only mammals which could fly and swim made it to the islands. Of the 24 native mammals, 21 are whales and dolphins. Two more are seals: the Hawaiian monk seal, which is endemic to Hawaii, and the northern elephant seal, which is the second-largest seal species. The last mammal species is Hawaii's only native terrestrial mammal, the Hawaiian hoary bat. The other 17 mammal species are invasive. The so-called "first wave" of invasive species were brought by the Polynesians when they first settled the islands. These are the Polynesian rat and the Kunekune, a Polynesian race of pig. After James Cook encountered Hawaii in 1778, European sailors introduced (both intentionally and inadvertently) mammals such as Norway or Brown Rats, black rats, house mice, feral cats, and feral goats. In 1883, the Indian grey mongoose was introduced to eat the abundant rodent populations on the islands.

In 1916, a group of brush-tailed wallabies escaped a zoo in Honolulu and established a colony in the Kalihi Valley, north of the city.