Hawaiian Rail - Systematics

Systematics

Considerable confusion has been created by the existence of two distinct forms. While it cannot be completely excluded that early specimens were collected on another island, only Oʻahu and Kauaʻi seem possible given the history of the specimens' collection, and only on the latter island is a similar-sized species now known to have once existed. However, the bones from Kauaʻi are in the upper size range of those found of sandwichensis, while the specimens of the lighter form are all of smaller birds.

On the Big Island, a smaller species of Porzana is now known from subfossil bones found on the southwestern slope of Mauna Kea, but this bird was only the size of a Laysan Crake; it may have been the bird named iao or ʻiao, which would place its extinction at a relatively recent date. In addition, there are some bones of a third species, approximately 15% larger than P. sandwichensis, found near Kailua-Kona.

The generally accepted theory is that the lighter birds represent immatures, and certainly only such specimens have been described as young birds (the Hanover specimen is labeled as "juvenile"), but since the exact collection localities are not known with sufficient detail, only DNA analysis could resolve this question, particularly since the recovered bone material can also be expected to yield analyzable DNA fragments.

At any rate, both light and dark birds are today treated as a single species, the junior synonyms of which are as follows:

• Rallus sandwichensis
• Rallus obscurus
• Pennula millei
• Pennula millsi
• Pennula wilsoni
• Pennula ecaudata

The last 5 names refer to the dark form. However, Rallus obscurus is something of a mystery as it is generally assumed that at the time of Gmelin's writing, the species was only known from light birds (which were described as sandwichensis on the preceding page of Gmelin's work), but he seems to have seen a specimen of his obscurus at the Leverian Museum (Stresemann, 1950).