Hawai’i only has two native mammals. One of them is a seal, and the other is a bat. However, if you go to the big island, you might see a lot more. Rats and mongooses (mongeese*? Mongoose? It turns out they’re all correct ) are both very common. The rat makes sense; rats have traveled all over the world by being stowaways on boats.
Interesting side note: the bubonic plague traveled on rodents from Asia to Europe during the Middle Ages. From there, they made their way to Hawaii to cause an outbreak of the Plague in 1900.
If it seems unlikely that mongeese made their way to the islands this way, you’re right. The true story is much dumber, and in my opinion, much funnier.
Rats don’t just cause disease, they also have a bad habit of needing to eat in order to live. Their little teeth and stomachs absolutely wrecked the sugarcane industry. Predictably, the plantation owners were ready to try anything to get rid of them.
Enter W.B. Espeut. He owned a plantation in Cuba that had a rat infestation and he thought up the idea of bringing in mongoose to try to fix his furry problem. He brought nine over from India, and in an article he wrote in 1872, they apparently ate all of his rats.
After that, plantation owners all over the tropics needed to have them. “Finally,” they thought, “an end to the problem.” But there’s just one issue: rats are nocturnal, meaning they are active at night. Mongooses, on the other hand, are diurnal, like most humans. Turns out they are not even awake at the same times. Needless to say, their unwelcome rats were totally fine, and now the plantation owners had a mongoose problem.
Of course, they don’t stay in the fields.
Most of the native birds to Hawai’i nest on the ground, because they have no native predators. These eggs make a delicious snack for rats, and later, for mongeese.
So, Hawai’i’s native bird population started to plummet. Nowadays, most of the birds in Hawaii are not native, and a lot of the native ones are endangered.
Moral of the story: make sure to double check the diurnality of animals you are trying to bring to new islands. Really, probably, don’t bring any new animals to islands.