The Laysanmillerbird was a subspecies of the millerbird, similar in appearance to the remaining subspecies, the Nihoa millerbird. Its dorsal side was brown, and its belly was grayish. Its name derives from its favorite food, several species of moths of the genus Agrotis commonly referred to as "millers".
Extinction
Very tame, it was abundant on Laysan, where it was endemic, in the 1890s. After the fateful introduction of domestic rabbits in 1903, which nearly denuded the island of vegetation in the next few years, the birds probably declined rapidly. Supposedly, there were 1500 still alive in April 1915 as reported by the USCGC Thetisexpedition, but a thorough 1911 census by the State University of Iowa expedition had found only "a few", as did a brief visit in February 1916. As land bird populations on Laysan fluctuate heavily and because there was considerable poaching for the Japanese millinery trade in the 1910s, the supposed 1915 figure cannot be discounted, but it seems highly improbable. At any rate, the 1923 expedition by the reported only one unconfirmed sighting which seems to have been erroneous. Thus, it can be concluded that the bird disappeared at some time in the late 1910s. As the vegetation disappeared, the bird suffered increased egg predation by Laysan finches, ruddy turnstones and bristle-thighed curlews, as well as increased competition for food and nesting habitat; a small patch of tree tobacco was the only locality left where the millerbird, the Laysan rail and the Laysan honeycreeper could nest with a reasonable chance of success. Additionally, the moths which formed its main food source became likewise extinct or exceedingly rare as their food plants were eaten by the rabbits, and thus the only significant food left were brine flies, which, though abundant, would also be utilized by the other land birds and the Laysan duck, all of which were more aggressive than the millerbird. It is most likely that the Laysan millerbird was the first of the three avian taxa to have gone extinct on Laysan, the last individuals of the apapane disappearing in a sandstorm around April 24, 1923 and the rail also disappearing around that time.
