Western Cattle Egrets, Bubulcus ibis were introduced into Hawaii in 1959. They are often seen riding the backs of livestock. They pick ticks and other insect predators from the backs of cattle and they eat insects and small invertebates and reptiles kicked up where the livestock walk.  They have few predators. This, combined with the somewhat beneficial relationship with livestock has facilitated the rapid spread of these birds virtually across the planet. They were originally believed to have come from Spain and Africa.