Audubon's shearwater underparts are white, as is the head below eye level. The iris is dark, the feet are dull pink with a black wash and black toenails, and the bill is grey, darker towards the tip, and with a pinkish hue. Males and females look alike. Immature birds do not have a distinct plumage, while the nestlings are covered with down feathers, grey above and whitish on the belly. It can be confused with the Manx shearwater ("P. puffinus"), which has white undertail coverts and in direct comparison a longer bill. Other similar-looking species are usually completely allopatric, though the largely
Trevor H. Worthy the Waitomo frog ("Leiopelma waitomoensis"). In the 1990s Worthy discovered several fossil bird species new to science, including the long-billed wren ("Dendroscansor decurvirostris") in 1991, Scarlett's shearwater ("Puffinus spelaeus") in 1991, and the Niue night heron ("Nycticorax kalavikai") in 1995. In 1991 he also described the Northland skink, a fossil skink species new to science. In 1998 Worthy excavated subfossil bones in Fiji, where he found remains of the flightless Viti Levu giant pigeon ("Natunaornis gigoura"), the Viti Levu scrubfowl ("Megapodius amissus"), the Viti Levu snipe ("Coenocorypha miratropica"), the giant Fiji ground frog ("Platymantis megabotoniviti"), and the small freshwater crocodile