Hawaiian Petrel

Pterodroma sandwichensis

Jim Denny, kauaibirds.com
  • PROCELLARIIDAE
  • Shearwaters, Fulmars, Petrels
  • 20,000

A fast-flying seabird that ranges thousands of miles over the central tropical Pacific, the Hawaiian Petrel nests only on the Hawaiian Islands. Although once lumped together with the Galapagos Petrel and known as Dark-rumped Petrel, recent work has shown that both are distinct species. The introduction of exotic predators to the Hawaiian Island breeding grounds poses a severe threat to the species, which is now endangered throughout its range.

Identification
Birds can sometimes be seen nearshore at dusk and dawn especially near Kauai. In flight, the Hawaiian Petrel's erratic, high-arching and swooping behavior identifies it as one of the Pterodroma petrels; and this is one of the larger species in the group, with longer, more pointed wings and tail, and a dark rump. To distinguish it from other species, note the distinctive black hood that forms a partial collar on the sides of the neck. The strikingly white forehead, less contrasting upperparts, and relatively larger size distinguish it from the Bonin Petrel, which is found in the same waters. Newell's Shearwater has a dark forehead, and flies closer to the surface, without the high-wheeling glides of the Pterodroma. The most similar-looking species is the Juan Fernandez Petrel which has only an indistinct or partial dark stripe on the underwing and a definite "M" across its upperparts. The Hawaiian Petrel may be heard giving distinctive calls near remote high-elevation breeding sites. Some calls sound like the yapping of a small dog. Another distinctive low-pitched call gave the species its Hawaiian name of "U'a'u".

Distribution and Population Trends
This petrel formerly nested in very large numbers at multiple sites on all of the main islands in the Hawaiian chain except Niihau but hunting of nestlings, habitat modification and the introduction of predators and disease-carrying mosquitoes eliminated the nesting populations closer to sea level so that remaining colonies are restricted to a few remote high elevation sites. The Haleakala National Park on Maui Island houses the largest known breeding population of 450-650 pairs and Kauai is suspected of having as many as 1,600 pairs of breeding birds, perhaps including a colony near the Hono O Na Pali Natural Area Reserve where birds have been heard calling. Small numbers have bred on Hawaii on both Mauna Loa and Mauna Kea. Fledgling Hawaiian Petrels disoriented by lights have been occasionally found on Lanai where colonies may occur at Kumoa Gulch and Lanai Hale and small numbers of calling birds have been heard on Molokai. Recent at-sea surveys estimate the population at approximately 20,000 individuals. These birds may range thousands of kilometers from their nesting colonies, even during breeding season.

Ecology
Hawaiian Petrels range far to find their widely dispersed food sources. They feed primarily on squid, but also fish, crustaceans and plankton found at the surface, and they are also known to scavenge. They do not seem to dive or swim underwater, and are seen more frequently when the wind is blowing at least 20-40 kms per hour. They are long-lived and lay only a single egg per year, making them very susceptible to population declines. They are believed to be monogamous and show mate fidelity. During their March to October nesting season they return to the same nesting burrows year after year, entering and exiting their burrows only under the cover of night. Radar studies on Kauai indicate that birds come and go from breeding areas in greatest numbers two hours after dusk and two hours before dawn. Currently threatened nesting habitat has forced them to adopt marginal, high-elevation sites, but historically they occupied low-elevation sites easily accessible to the ocean. They range up to 1,500 kms from the Hawaiian Islands during breeding season, with only rare sightings in these waters from January through March.

Threats
By far the most serious threat to the species is depredation of eggs and young by feral predators, notably cats and mongooses. Even incidental occurrences of single individual predators can decimate a nesting colony. The adults are evolutionarily defenseless against introduced predators. Avian malaria was found in blood samples of Hawaiian Petrels in the 1960's and this disease may have killed off low elevation breeders. According to population models, this species could be driven to extinction in a few decades if predation by feral predators is not controlled. Occasional mortality also occurs from collisions, notably with powerlines and fences near breeding sites. Fledgling birds are sometimes grounded when they become disoriented by lights on their nocturnal first flight from the inland breeding sites to the ocean.

Conservation
The species was federally listed as Endangered in 1967. Remote locations of successful breeding sites make it difficult to protect this species. National Park Service and Hawaii Division of Forestry and Wildlife biologists run a predator control program at Haleakala Crater on Maui Island. The Hawaii Division of Forestry and Wildlife has initiated surveys to locate breeding colonies on Kauai. An experiment using call playback techniques developed by Audubon's Seabird Restoration program in the Galapagos Islands, demonstrated that the closely-related Galapagos Petrel can be lured to nest in artificial burrows, a tool that may prove useful to relocating breeding pairs of Hawaiian Petrels into predator-free areas in the future. A program to shield streetlights is in effect in Hawaii to help petrels and shearwaters avoid collision and volunteers help to capture grounded fledglings for release in the ocean.

What Can You Do?

The Endangered Species Act has helped protect the Hawaiian Petrel and made it possible to learn critical information about its biology. Audubon continues to work to ensure that this vital legislation is being used to protect our publicly-owned wildlife resources. Check out http://policy.audubon.org/ to learn of the latest news about the Endangered Species Act and how you can help. To learn more about other species protected under this legislation, visit: http://endangered.fws.gov/

Join Hawaii Audubon Society. A chapter of National Audubon, the Hawaii Audubon Society works to protect and educate people about Hawaii's birds. For more information visit http://www.audubon.org/chapters/hawaii-audubon-society

References
Birdlife International. 2000. Threatened Birds of the World. Lynx Edicions, Barcelona.

BirdLife International (2006) Species factsheet: Pterodroma sandwichensis, Hawaiian Petrel http://www.birdlife.org/datazone/speciesfactsheet.php?id=3896

Day, R.H., and B. A. Cooper. 1995. Patterns of movement of Dark-rumped Petrels and Newell's Shearwaters on Kauai. Condor 97:1011-1027.

Ehrlich, P.R., Dobkin, D.S., and D. Wheye. 1992. Birds in Jeopardy. Stanford University, Stanford, CA.

Harrison, C.S. 1990. Seabirds of Hawaii. Cornell University Press, Ithaca.

Harrison, P. 1983. Seabirds: An Identification Guide. Houghton Mifflin, Boston.

Pratt, H.D., P. L. Bruner, and D. G. Berrett. 1987. The Birds of Hawaii and the Tropical Pacific. Princeton University Press, Princeton, NJ.

Shallenberger. R.J. 1984. Hawaii's Birds. Hawaii Audubon Society, Honolulu, HA.

Simons, T.R., and C. N. Hodges. 1998. Dark-rumped Petrel (Pterodroma phaeopygia). In The Birds of North America, No. 345 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists' Union, Washington, D.C.