Of the three rat species found in Hawaii, the black . rat, because of its size and arboreal behavior is considered the greatest threat to native Hawaiian forest birds. Rats also compete with forest birds for food items . such as native snails, insects, fruits, and seeds. Polynesian rats first arrived in Hawai`i with the . Polynesians (approx. 400A.D.) and black and Norway rats arrived with Westerners in the 1780s. Some species of rats can swim over a mile in open water, and can tread water for up to three days. Some species of rats can travel through sewer pipes and dive through water plumbing traps.