The first Ancient Hawaiians to arrive on Hawaii island lived along the shores where food and water were plentiful. Flightless birds that had previously known no predators became a staple food source. Early settlements had a major impact on the local ecosystem, and caused many extinctions, particularly amongst bird species, as well as introducing foreign plants and animals and increasing erosion rates. The prevailing lowland forest ecosystem was transformed from forest to grassland; some of this change was caused by the use of fire, but the main reason appears to have been the introduction of the Polynesian Rat ("Rattus exulans").