The Poo-uli (Melamprosops phaeosoma), a Hawaiian honeycreeper discovered on the island of Maui in 1973 and now near extinction, is represented in museums by only two specimens. Based on the first observations of a nesting pair and re-examination of the two specimens, we describe the adult male and female, eggshells, nestling, and fledgling Poo-uli. Poo-uli are sexually monochromatic but males are brighter. The male is brown above, whitish below, and has an extensive black mask bordered with gray on the crown and a distinct white auricular patch. The female differs in having a similar facial pattern not as sharply demarked and in having a grayish wash below. The observed fledgling resembled the adults but was paler brown above and whitish below and had a much smaller black mask and pale mandible. We tentatively assigned both museum specimens to first basic plumage because they resembled the adult female but retained some pale juvenal coloration in the mandible. We also determined from dissection that the holotype was an immature male; we could not determine sex of the paratype. The nest was an open cup of twigs and bryophytes with a thin lining of fern rootlets. The nest contained eggshell fragments with brown-gray speckling against a whitish background. The nests, eggshells, and nestlings resemble those of other Hawaiian honeycreepers.
