Description of nests, eggs, and nestlings of the endangered nightingale reed-warbler on Saipan, Micronesia

Abstract

We describe the first verified nests, eggs, and nestlings of the Nightingale Reed-Warbler ( Acrocephalus luscinia ), an endangered species endemic to the Mariana Islands, Micronesia. Nest composition, nest dimensions, and eggs were studied on the island of Saipan. Nests were located within three habitat types: upland introduced tangantangan ( L eucaena leucocephala ) forest, a native mangrove ( Bruguiera gymnorrhiza ) wetland, and a native reed ( Phragmites kark a ) wetland. Nesting substrates included five native and two introduced tree species and one native reed species. Nests were composed primarily of dry vine stems, needle-like branchlets of ironwood ( Casuarina equisetifolia ), and tangantangan petioles. Nests were compact to bulky in construction and were secured to a forked arrangement of branches or stems. The background color of eggs ranged from white to cream to ivory-buff. Eggs were spotted, speckled, and blotched with gray, brown, black, and rust colored markings. Clutch size was 2–4, with a mode of two. Hatchlings were altricial with closed eyelids and devoid of natal down with dark gray to black skin. Nestlings examined prior to fledging resembled the adult plumage, except for the lack of the yellow supercilium found in adults. The nests and eggs have some characteristics similar to those of other Acrocephaline warblers found throughout Micronesia and Polynesia.