Overview
The Nihoa Millerbird (Acrocephalus familiaris kingi) is a tiny, critically endangered reed warbler endemic to the rugged volcanic island of Nihoa in the Northwestern Hawaiian Islands. Possessing modest olive-brown and buff plumage, this hyperactive songbird earned its common name from its voracious appetite for ‘miller’ moths (noctuid moths). Having survived for centuries on a single, isolated 170-acre volcanic rock, it represents one of the most remarkable stories of island avian tenacity and modern endangered species translocation.
Biology and Physical Characteristics
The Nihoa millerbird possesses an unassuming appearance tailored for life in dense, windswept scrub. Its upperparts are a warm grayish-brown, while the throat and breast fade into pale cream and buff. A slender, straight, sharp-pointed bill enables the bird to probe tiny crevice cavities in volcanic rock and glean hidden caterpillars from beneath goosefoot foliage. Its legs and feet are long and robust, conferring agile hopping ability through tangled island brush without touching the open ground.
Behavior and Ecology
Nihoa millerbirds are intensely territorial, inquisitive, and active foragers that spend their days continuously searching through dense shrub canopies for insect prey. Males proclaim territories with a cheerful, melodious song consisting of short whistles and warbles. Pairs are monogamous, constructing cup-shaped nests woven from dried grasses, stems, and seabird feathers hidden deep inside thick shrubs. Both parents diligently feed the clutch of two eggs with soft-bodied caterpillars and moths.
Conservation and Human Impact
The nomination of the Nihoa millerbird as Critically Endangered stems from its hyper-restricted geographic range; with its sister subspecies on Laysan driven to extinction in the 1920s by introduced rabbits, the entire global population was confined to a single island vulnerable to catastrophic hurricanes or accidental invasive predator introductions. In an extraordinary conservation milestone between 2011 and 2012, biologists translocated 50 individuals to restored habitats on Laysan Island, where a flourishing second population now guarantees insurance against total extinction.
Interesting Factoid
The Nihoa millerbird lines its cup-shaped nest almost exclusively with the soft, white downy feathers shed by nesting Great Frigatebirds and Red-footed Boobies that share its tiny volcanic island home.
Last updated: October 2026