Bonin petrel

The Bonin petrel and the closely related mottled petrel are the only Pterodroma petrels with a fish dominated diet. Principal prey items are fish from the family Myctophidae (lantern fish) and Sternoptychidae (hatchetfish). Squid from the family Ommastrephidae are also consumed.[3] All of these prey are midwater residents that use photophores and migrate to the surface during the night to feed; thus it is assumed that Bonin petrels are nocturnal feeders that seize prey at the surface while resting on the sea or in flight. Bonin petrel eyes contain high levels of the pigment rhodopsin which aids nocturnal vision. The Bonin petrel is usually solitary at sea, but is occasionally seen in large multi-species flocks. Like all procellariids the Bonin petrel has a modified area of the gut known as a proventriculus which partly digests prey to create stomach oil, an energy rich oil which is lighter to carry than prey.

A Bonin petrel trapped in the sand on Midway Atoll by the 2011 Tōhoku earthquake and tsunami, before being rescued.

The Bonin petrel breeds in dense colonies, on islands in the Northwestern Hawaiian Islands; French Frigate Shoals, Laysan, Lisianski Island, Pearl and Hermes Reef, Midway Atoll and Kure Atoll; and on the Volcano Islands and Bonin Islands south of Japan. Colonies are only visited by birds at night, with birds usually arriving soon after sunset.[4] Nesting occurs in the winter in order to avoid competition for burrows with other nesting procellariids. In the Northwestern Hawaiian Islands the nesting season sometimes overlaps with the larger wedge-tailed shearwater, which will evict and even kill Bonin petrel chicks in order to use the nesting burrows. Both parents participate in digging burrows, which are usually dug in sand or hard coral substrate, and are between 1 and 3 m long. Pairs are territorial, and will defend an area of around 2 m around the burrow entrance. They also display philopatry, returning to the same burrow in consecutive years, redigging the burrow if it has collapsed. Burrows in harder coral substrate are less likely to collapse than those dug into sand.[4]

Bonin petrel chick

The species is thought to mate for life (like other Procellariiformes); pairs undertake mating flights consisting of pairs chasing and calling at each other over the colony prior to laying. A single egg is laid by a pair each breeding season, if it is lost then no attempt is made to re-lay. Laying occurs in late January. Both parents incubate the egg, with incubation stints of eight days for the male and six days for the female. Hatching occurs after around 50 days, around mid-March. The chicks are semi-altricial at hatching, covered in light grey down, and are brooded by the adults for two days after hatching, after which both parents feed at sea and return at night to feed the chick. Chicks are fed stomach oil and small items of prey. Chicks fledge around 80 days after hatching, in early June.

After the breeding season both chicks and adults migrate northwards to the seas off Honshū and Sanriku in Japan. The timing of the migration is partly influenced by sea surface temperatures. Birds begin to disperse south and east again in August and begin to return to their breeding islands in September. During the breeding season birds feed in the waters surrounding breeding islands. The species has not been recorded in the east Pacific.