The last two species are endangered. In the upper valley are many native species of songbirds, such as the apapane ("Himatione sanguinea") and Oahu amakihi ("Hemignathus flavus"), along with non-native species of mynah, cardinal, dove and ricebird. Feral pigs were introduced to the valley by the first Polynesian settlers. While this is an ideal environment for the pigs, these animals are a serious threat to the rest of the valley. The expanse of land in Kahana Valley from the sea to the mountains contains many different vegetation zones. The lowlands consist of koa ("Acacia koa"), hibiscus, hala ("Pandanus tectorius"), and pasture. Further up the valley, in the wetter areas, the dominant vegetation consists of mountain apple ("Syzygium malaccense"), strawberry guava ("Psidium littorale"), ti ("Cordyline fruticosa") and bamboo. There are two hiking trails in the valley, both of which do not require permits and are suitable for whole families. The first is Kapa'ele'ele Ko'a and Keaniani Lookout Trail. It is a mile long loop that takes a decent hiker roughly an hour. The second is the Nakoa Trail, which is named so for the numerous koa ("Acacia koa") found along this 2.5-mile trail through tropical rainforest. Hikers on this trail can swim in the Kahana stream, which is traversed twice. There are ten campsites located on the beach which can be used by permit only. Hunting is also permitted within designated boundaries on weekends and holidays only, and by permit only.