The 70 forms shown as currently existing include 13 in peril, with steps marking the decades of their last known records. Yellow represents prehistoric forms. These may be categorized as established, not established, or uncertain. Few of those deemed uncertain or not established in 1933 have persisted until today. Introductions continued during the 1940's and 1950's but thereafter were severely curtailed by stronger governmental restrictions on importation of wild birds.
Factors affecting population levels differ markedly among the groups.
Although current status of species within all groups is fairly well understood, assessing meaningful trends for species is difficult for lack of comparable quantitative data on statewide populations over time. 96734 References A.O.U. 1983. Check-list of North American birds, 6th ed. Caum, E.L. 1933. The exotic birds of Hawaii.