Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Procellariiformes
Family: Procellariidae
Genus: Puffinus
Species: P. gavia
Binomial name: Puffinus gavia
Common name: Fluttering shearwater, Forster's Shearwater

Puffinus gavia is a small dark brown and whitish shearwater that is endemic to New Zealand. They are 31–37 cm; 225–425 g and with a wingspan of 76 cm. 
Puffinus gavia is a species that is a common and widespread and is endemic to New Zealand. The larger colonies are found in the Three Kings group, Moturoa group, Motuharakeke (Cavalli Islands), north-west Chickens, Bream Islands, Mokohinau group, Channel Island, Mercury group, Ruamahuanui (Aldermen group) and Trio Islands and many other islands in Cook Strait. Fledgelings, and possibly some adults, move towards the east and south of Australia in February, but most remain near to breeding colonies throughout the year (Marchant and Higgins 1990, Powlesland and Rickard 1992) Its natural habitats are open seas and rocky shores. 
This species breeds on small, vegetated islands and rock stacks. It nests in colonies in burrows under grass, scrub or coastal forest, but occasionally breeds in rocky cavities (Marchant and Higgins 1990). The breeding biology of the species is very poorly known, but laying is believed to begin in early September, and chicks fledge from late January (Powlesland and Rickard 1992). Birds feed mostly on fish and some coastal krill (Marchant and Higgins 1990).

At sea, they congregate in flocks and fly generally in a zigzag course, with a very rapid movement of the wings and not far above the water, showing first the dark plumage of the upper surface and then the white underparts as they simultaneously dip towards the water.

A video by Pieter de Groot Boersma showing a bird diving for food.

Puffinus gavia by JJ Harrison.jpg  

Puffinus gavia by Duncan.jpg

Thanks to Wikipedia for text and information