Common Mynas are probably the most frequently observed bird species in Hawaii. To me, they were like an equivalent of European Starlings, which are not found in Hawaii. They were common in lawns and gardens around the island, and at night they would gather at large communal roosts, making quite a racket as they settled in at dusk. They were introduced from India in 1865 to control insect pests.
Saffron Finches are very bright birds that were introduced from South America in the 1960s. The book I have, from 1997, says that they are found on the dry side of the island, but eBird shows them over most of the island, so I believe they've spread in the last decade or two. They are still more common on the dry side, though.
Yellow-billed Cardinals were frequently encountered but usually singly or in pairs. They were introduced from South American in the 1970s. They are generally limited to the parks and gardens in the lower elevations, but we did see one at Pu'u Huluhulu on the Saddle Road at an elevation of about 6,600 feet, which is unusual.
Watch for another post on Hawaii's wildlife coming soon. . . .