Editor's Note: This account contains life history information for both Hawaiian and Laysan rails. Future revisions will provide separate treatments for these species.
Before the arrival of humans, all the main Hawaiian islands probably were populated by flightless rails, some islands having up to 3 species each. At least 12 species are known, 10 from fossil remains only (Olson and James 1991). All were short-billed “crakes” that have been referred to the genus Porzana . The 2 flightless species that are known to have survived into the historic period in the Hawaiian Archipelago are also now extinct, exemplifying the extreme vulnerability conferred by flightlessness. Whereas the Hawaiian Rail is known from 7 specimens only, the last taken in the mid-1800s, the Laysan Rail is abundantly represented in collections and became extinct in the mid-1940s. Both were relatively small species, although even smaller ones are known among the archipelago's fossil rails. Some of the fossil species probably persisted into the historic period; Perkins (Perkins 1903: 453–454) was confident that a rail existed on Mol-oka‘i I. in the nineteenth century.
The native name moho for the Hawaiian Rail is the same as is used throughout Polynesia to refer to small rails of the genus Porzana, and it is unfor-tunate that Lesson (Lesson 1830b) introduced confusion by transliterating the Hawaiian name ‘o‘o as Moho, which has now come down to us as the generic name of most of the Hawaiian honeyeaters (Meliphagidae). English names of the rails follow American Ornithologists' Union 1998a, although Taylor (Taylor 1998) more consistently uses the names Laysan Crake and Hawaiian Crake instead.
Specimens and drawings of the Hawaiian Rail were among objects obtained in 1779 and brought back by ships of Captain James Cook's third and final voyage (Medway 1981). Much confusion ensued in the literature concerning the number of species of flightless rails to be recognized in the historical record of the main islands, but none of the existing evidence indicates more than one.
The Laysan Rail was first noted during the visit of the Russian ship Moller to Laysan I. in 1828 (Kittlitz 1834), but not until 1891 were specimens that had been brought from Laysan obtained by Henry Palmer and sent to Walter Rothschild in England. Not long thereafter, Palmer went to Laysan himself and collected many additional specimens, including live birds that made it safely back to England. For an unexplained reason, the original description of the new species, which was Rothschild's to name, was delegated to the artist F. W. Frohawk (Frohawk 1892); this was his only nonpictorial contribution to Hawaiian ornithology.
It is not known how many separate colonizations gave rise to the radiation of Hawaiian flightless rails, although a minimum of 3 seems likely (Olson and James 1991). Because of the differences in their plumage, the Laysan and Hawaiian rails were presumed to have descended from different ancestral species of Old World rather than New World origin, an assumption that was recently confirmed by DNA evidence. Each had once been placed in its own monotypic genus (Porzanula and Pennula, respectively) on the basis of characters associated with flightlessness that are no longer considered to be of generic value (Olson Olson 1973b, Olson 1973a).
The 2 species considered here are the only flightless, insular species of Rallidae to be treated in the Birds of North America series. Because both are extinct, few details are known about their life histories compared with extant continental North American birds. Therefore, some comments on rails in general may help fill in the gaps and bring these 2 birds into perspective.
Rails belong to a distinct family of Gruiformes not especially closely related to any other living birds. In the Tropics, many species inhabit forests, which was probably the primitive habitat, but in temperate continental areas, rails generally inhabit marshes, which are discontinuous and often ephemeral, necessitating extensive postbreeding wandering by individuals in search of more habitat. This wandering, coupled with an excellent ability for overwater dispersal, has resulted in rails' successful colonization of most oceanic islands of the world, where, in the absence of predators, they quickly become flightless (Olson 1973b). Because they are vulnerable to predation, hundreds of populations of flightless rails have probably become extinct in the period of human conquest of the oceans (Steadman 1995b).
Very few rails have specialized feeding habits; most are generalized, opportunistic omnivores. They are capable of surviving under harsh conditions such as on Laysan or Ascension Is., where the birds were heavily dependent on seabird colonies (Olson 1973b). In places such as the main Hawaiian islands, rails would probably have occupied most vegetated habitats, and they may have relied to a considerable extent on land snails (Gastropoda) for food. Probably only predation, particularly of nests, causes temperate continental rails to be restricted to marshes; otherwise they might be expected in habitats as diverse as those that they occupy on oceanic islands.
The great number of flightless insular populations of rails has been produced by relatively few continental genera—mainly Rallus, Gallirallus, and Porzana, and to a lesser extent various gallinules. Apart from some of the rails of New Zealand and the Chatham Is., insular rails usually exhibit little morphological diversity. Other than the adaptations associated with flightlessness and the generally more robust hindlimbs associated with being more terrestrial, rails appear to require little in the way of adaptations to insular environments, so depending on the ancestral genus, flightless rails tend to differ among themselves mainly in plumage, size, and amount of reduction in the flight apparatus. Morphologically and probably behaviorally, one flightless rail is much like another and the Hawaiian species are unexceptional.