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Bonin Petrel

Pterodroma hypoleuca
Bonin Ptrl

Petrels on the Rebound

The Bonin petrel is a small, burrow-nesting seabird that breeds primarily in the Northwestern Hawaiian Islands (NWHI) and in smaller numbers on several islands in Japan, including Volcano Island and Bonin Island. Today, Midway Atoll National Wildlife Refuge hosts the world’s largest Bonin petrel population.

While Midway Atoll’s Bonin petrel population was estimated at over 500,000 individuals in the late 1930’s, the accidental introduction of rats in 1943 caused numbers to plummet to less than 5000 in the 1980’s. After the successful rat eradication in the 1990’s, the Bonin petrel population on Midway has become explosive with a current population estimated at close to a million individuals.

Despite the large breeding population in the NWHI, little is still known about these secretive birds. What has been observed are Bonin petrels foraging for fish and squid, and during the fall they come ashore en masse as they make their way to their breeding islands. They spend their days either in their burrows or at sea, and starting at sun down, they emerge from their burrows or return from foraging, and congregate in the air above their nesting grounds by the hundreds of thousands.

These petrels are monogamous and return to the same burrow every year; arriving in August and spending the fall months courting, establishing pair bonds, and remodeling or excavating their burrows. In their personal burrow, which can be up to three meters long and a meter deep, petrel pairs build small nests using bits of grass and ironwood needles, into which they lay their eggs. Bonin petrels lay one egg per year, and no re-laying will take place if the egg is lost. After about a month, the egg hatches into what could easily be confused with a large dust bunny except for a small black bill.

Though the average lifespan of Bonin petrels is estimated at 15 years, the current record for the oldest known Bonin petrel comes from Tern Island within the NWHI where two Bonin petrels were found to be over 30 years old. In spring of 2014, a Refuge Manager recovered a Bonin petrel on Midway that was banded 19 years old as an adult.  These recent discoveries highlight the fact that the life habits and lifespan of Bonin petrels, like many other burrowing bird species, still remain a mystery. Long-term monitoring administered by the U.S. Fish and Wildlife Service can help protect these fascinating seabirds, and the island and ocean habitat they depend upon.

Facts About Bonin Petrel

Diet
Feeds on small fish and squid by dipping or surface-feeding on the ocean surface.
Life Span
15 years (Although, recent discoveries have proved they live longer!)
Size
Length: 30 cm (12 in); wingspan: 63-71 cm (25-28 in) 
Page Photo Credits — ©Dan Clark
Last Updated: Jun 09, 2016
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