The lush vegetation of the high islands includes creepers, ferns, and tall trees in the interior, while coconuts, bananas, and grapefruit grow on the coast. Avocados and papayas are so abundant that the locals feed them to their pigs. On the elevated atolls the vegetation in the fertile volcanic center contrasts brusquely with that of the infertile limestone makatea. Taro and yams are subsistence crops. The au is a native yellow-flowered hibiscus. The flower of this all-purpose plant is used for medicine, the leaves to cover the umu (earth oven), the fiber for skirts, reef sandals, and rope, and the branches for walling native cottages on outer islands. November-March, the flamboyant trees bloom red.
The only native mammals are bats and rats. The mynah is the bird most often seen, an aggressive introduced species that drives native birds up into the mountains and damages fruit trees. By 1989 only about 29 examples of the Rarotonga flycatcher or kakerori remained because of attacks on the birds' nests by ship rats. Fortunately a local landowners' group, the Takitumu Conservation Area, took an interest in the kakerori's survival and began laying rat poison in the nesting areas during the breeding season. By 2005 there were 265 kakerori.
The forest birds of the Cook Islands include the Atiu swiftlet (kopeka), blue lorikeet (kuramo'o), chattering kingfisher (ngotare), common mynah (manu kavamani), Cook Islands fruit dove (kukupa), Cook Islands reed warbler (kerearako), long-tailed cuckoo (karavia), Mangaia kingfisher (tanga'eo), Pacific pigeon (rupe), Rarotonga flycatcher (kakerori), and Rarotonga starling ('i'oi).
Shorebirds include the bristle-thighed curlew (teue), grey duck (mokoro rauvai), Pacific golden plover (torea), spotless crake (mo'omo'o), and wandering tattler (kuriri).
Among the seabirds are the black noddy (rakia), blue-grey noddy (kara'ura'u), brown booby (kona), brown noddy (ngoio), great crested tern (kakavai maui), great frigatebird (kota'a nui), masked booby (lulu), red-footed booby (toroa), red-tailed tropic bird (tavake), sooty tern (tara), white-tailed tropic bird (rokoa), and white tern (kakaia).
Unfortunately the activities of local sharpshooters have made the Cook Islands less attractive as a bird-watching venue, and spearfishing using scuba gear has done much damage to the marinelife. To control this, five lagoon areas around Rarotonga have been closed to fishing and shell collecting since 1998 under a traditional system known as ra'ui. In one of the ra'ui areas, the number of fish species increased from 14 to 31 in the first two years. Humpback whales can sometimes be seen cruising along the shorelines July-September, having migrated 5,000 km north from Antarctica to bear their young. Pilot whales (up to six meters) are in the Cooks year-round. In 2001 the Cook Islands declared its large exclusive economic zone a whale sanctuary. Sharks are not a problem in the Cook lagoons.