ARTICLES ON HAWAIIAN BIRDS AND BIRDWATCHING AND OTHER PACIFIC WILDLIFE

The Hawaiian Petrel (Pterodroma sandwichensis): Distribution, Population Status and Species Status

Almost the entire Hawai'i population was apparently wiped out in the 1930's due to intensive human exploitation and devastation by introduced species such as Mongoose. Excessive loss of birds occurred on Maui at Haleakala Crater through predation by cats, dogs and Mongoose and resulted in 70% nesting failure. Recent intensive trapping and habitat protection has helped to improve nesting and fledging success (Harrison 1983, Ainley et al. 1997).

Although Hawaiian Petrels are not currently known to be established on O'ahu, excavations have shown that it was once the most abundant seabird on the island. Apparently Hawaiian Petrels were reserved for Hawaiian royalty and both young and adult birds were eaten, although the adults were salted first to mask the unpleasant fishy taste that they possessed. On Hawai'i birds were abundant nesters on the lava fields between Mauna Kea and Mauna Loa, and birds were caught by distracting them with large fires, which had the same effect as today's street lights.

Population estimates for the species are mainly based on at-sea numbers, as it is extremely hard to estimate numbers in the breeding colonies, as these are remote, hard to reach and in areas where nest surveys would be detrimental to both the birds and the surrounding habitat. Harrison (1990) states the following populations from various sources between 1981 and 1988 - Kaua'i: ? (no estimate but breeding confirmed); O'ahu: 0; Maui: 400-600 pairs; Moloka'i: ? (no estimate but breeding suspected); Lana'i: 30 - 50 pairs; Hawai'i: 0 (no estimate but breeding confirmed).

Spear (1995) estimated from at-sea densities that the world population of Hawaiian Petrels was 19,000, with at least 5,000 pairs nesting on Kaua'i and 1,600 pairs on Maui (Ainley 1997). In 1992 the Hawai'i population was estimated at only 400 - 600 breeding pairs, with a total population of 2000 individuals - this means that the number present around the Islands has been repeatedly under-estimated. Note that Ainley (1997) reported observing maximum nightly fly-overs at Hanalei as 1,055 individuals in early May 1993 and 1,103 in late May 1994 and on Maui 300-500 birds per night - more or less the number reported in 1992 as being the entire population!

Numbers of birds seen flying inland at sites on the North Shore of Kaua'i during 1998 - 2001 did not approach anywhere near these totals (pers. obs.), although the observations were not intended as a population estimate and further research may find that the population truly is at the level found by Spear (1995). New research on this was being instigated during 2001.

Left: The mountains above Hanalei Bay are the nesting grounds for the majority of Kaua'i's Hawaiian Petrels. At dusk many birds may be seen collecting in the bay before gaining height and flying in overland to the cooler and wetter upland areas. The species nests under vegetation such as ferns.

At night near the colonies the birds can be heard calling loudly, giving their distinctive "u-a-u" calls. This sound was obviously well-known to the native Hawaiians, as they named this species Ua-u.

Nesting Biology

Hawaiian Petrels return to their colonies between March and April and depart in October and November. The colonies on Maui on the rim of the Haleakala Crater are between two and three thousand meters above sea level and are possibly the highest seabird colonies in the World. The effect of being forced to nest in these high altitudes is that the species initiates breeding a month earlier than they did just 40 years ago, when they nested at lower elevations. On the nesting grounds the species dig substantial burrows wherever the soil allows, although they will also commonly nest under rock crevices.

Males and females will alternate the incubation periods. Females will incubate for the first few days but switches over with the male after this time, who takes on a long incubation shift. On average the shifts last about twelve days. During this time the birds do not eat, drink or defecate and they minimize their energy expenditure by spending almost the whole time asleep or dozing. Also during this time the birds metabolize fats which produces water as a by-product. The incubation of the egg takes fifty-five days. The chicks usually hatch in July or August and are born with a soft, powdery down which is replaced after a fortnight by a slightly heavier down. Chicks spend most of their time sleeping, although they are quite capable of moving around the nest burrow. Both adults spend their time flying to sea to feed and bring food home for the chicks. The growth rate of the chicks is extremely fast and a young Hawaiian Petrel can double it's weight in one sitting! The meal can vary from 10 to 110 grams, the latter figure represents more than one quarter of the adult birds weight. This amount of food is probably the most an adult bird could carry. The weight gain of the chick can be very erratic with a gain in weight one week and then a shrinking in size the next, when they receive no food for a while. "Stomach oils, nine times richer in calories than fish, is helpful as a dietary reserve during starvation periods - chicks retain some in their stomachs even after they have eaten nothing for ten days" (Harrison 1990).

Hawaiian Petrels feed almost exclusively at night where they search for Lanternfish, Hatcherfish, Goatfish and similar species, which they find near the surface of the water. Feeding probably takes place with the bird sitting on the water and dipping it's head into the sea. occasionally a bird will be observed feeding during the day, but they are probably only picking up easily obtainable scraps floating on the surface. Apparently Hawaiian Petrels eat a higher proportion of fish than other Petrel species elsewhere (Harrison 1990). Most Petrels are estimated to feed within eighty kilometres of the Islands.

Feeding visits drop to just one or two in the final month and the chicks weight crashes, this however helps to spur the bird into leaving the nest and going to sea to find its own food. Some individuals are deserted by their parents up to six weeks before they fledge, whilst others are fed right up to the day of departure. Once the chicks leave they will not return to land again for several years, when they will return to nest.

The fledgling rate of the species depends on the location where the birds are born. On Maui only about a quarter of chicks used to fledge due to predation by cats and mongoose (amongst other species), recent control measures have helped increase this rate to "normal" fledging levels. On Kaua'i where mongoose are not established the species enjoys a high success rate, although cats, dogs and rats still take their share of young birds. Pigs also uproot burrows and expose the chicks to the weather and predators.

Collision of Hawaiian Petrels with power cables and urban lights

Every year a few (up to 20 or so) Hawaiian Petrels (Pterodroma sandwichensis) along with hundreds and sometimes thousands of Newell's Shearwaters, are grounded by colliding with power cables or after becoming disorientated by urban lighting. Of these many are killed or injured but thanks to an island-wide initiative those individuals which are unharmed or are treatable are collected, taken to fire stations and then rehabilitated and released back into the wild. On Kaua'i up to 20 birds may be released in a year. It is also important to remember that most of these birds are newly fledged and on their first flight to the ocean, if the population is bereft of these young birds then the long-term outlook for the entire population could be bleak. The Hawaiian Petrel however, does seem to be less attracted to urban lights than other Hawaiian Shearwaters and Petrels and this obviously results in fewer birds being found by the roadside/near lighted areas, although a smaller population of this species also has a direct effect on the numbers found.

Telfer et al. (1987). state " Every year more than 1,000 fledglings of three threatened or endangered procellariform seabird species are attracted to bright coastal lights on the Hawaiian island of Kaua'i. These seabirds, apparently on their first flight to the ocean, become disorientated around bright lights and crash into buildings, wires, tall vegetation and vehicles. Beginning in the early 1960's this problem became increasingly acute as Kaua'i's urban areas grew and the number of high-intensity lights increased. In response we initially instructed the public to release birds by tossing them into the air near the ocean. Since 1978, however, we asked Kaua'i residents to collect and turn in the birds at 1 of 12 "Shearwater aid stations" that we set up around the island."

Hawaiian and Galapagos Petrels recognised as two separate species.

The two species of Dark-rumped Petrel, which were formally considered conspecific but were given full species status by the American Ornithologist's Union (AOU) in August 2001, and are now treated as Hawaiian Petrel (Pteredroma sandwichensis) and Galapagos Petrel (Pteredroma phaeopygia).

In Hawaiian waters it is fairly safe to assume that all "Dark-rumped" Petrels are Hawaiian Petrels, rather than vagrant Galapagos Petrels, however there is at present no certain way to identify one species from the other without capture and sampling. Presumably all birds flying inland to nest are Hawaiian Petrels, whereas individuals at sea could conceivably be of either species, especially in the South Eastern waters of Hawai'i. For recording purposes though it is best assumed that all Dark-rumped Petrels in Hawaiian waters are sandwichensis.

The Galapagos Petrel (Pteredroma phaeopygia) breeds in the Galapagos Islands (Ecuador) on Santa Cruz, James, San Cristobal, Floreana and Isabela and in the non-breeding season disperses eastwards towards the South American littoral, extending to seas west of Mexico and Panama and south to the Gulf of Guayaquil, Northern Peru and the Humboldt current (Harrison 1983, del Hoyo 1992, Ainley et al. 1997).

Breeding starts in January or May in the Galapagos Islands, depending on locality and in early May on Maui (Hodges 1994) and late May on Kaua'i (Ainley 1997; Melgar pers.obs. 2001). The species is a colonial nester in burrows or crevices and hollows in lava. One egg is incubated for 52 - 56 days, with stints of 10 - 13 days for adults. Fledging occurs at 110 - 117 days.

The total population of both species was estimated at about 1500 pairs in 1992 (del Hoyo 1992), but recent habitat protection for both populations and a re-assessment of the Hawai'i population probably means the true figure is higher. As stated above Spear (1995) estimated from at-sea densities that the world population of Hawaiian Petrels was 19,000, with at least 5,000 pairs nesting on Kaua'i and 1,600 pairs on Maui (Ainley 1997). In 1992 the Hawai'i population was estimated at only 400 - 600 breeding pairs, with a total population of 2000 individuals - this means that the number present around the Islands has been repeatedly under-estimated. Note that Ainley (1997) reported observing maximum nightly fly-overs at Hanalei as 1,055 individuals in early May 1993 and 1,103 in late May 1994 and on Maui 300-500 birds per night - more or less the number reported in 1992 as being the entire population!

In the Galapagos a thriving population once existed but as in Hawai'i the species suffered high predation by cats and dogs as well as habitat destruction, and the population dropped to about 1000 pairs, and resulted in under 20% nesting success. Major conservation programmes underway in the Galapagos Islands, including eradication of alien predators, provision of safe nesting areas and transfer of chicks to predator-free islands to found new colonies has helped to increase the population in recent years.

Both species feed mostly on squid and fish and prey is taken either by surface-seizing or is caught on the wing by dipping (Harrison 1983). Further studies are required to learn the full range of food items taken by both species.

Further information can be found at the following site: http://montereybay.com/creagrus/DRPE_id.html

References:

AINLEY, D.G.; PODOLSKY, R.; DEFOREST, L. and SPENCER, G. 1997. New insights into the status of the Hawaiian Petrel on Kauai. Colonial Waterbirds 20 (1): 24-30.

BROWNE, R.A. , ANDERSON, D.J. et al. 1997. Genetic diversity and divergence of endangered Galapagos and Hawaiian Petrel populations. Condor 99: 812-815.

CARLQUIST, S. 1980. Hawaii: A natural History. Pacific Tropical Botanical Garden, Lawai, Kaua'i.

CONANT, S. 1980. Recent records of the 'ua'u (Hawaiian Petrel) and 'a'o (Newell's Shearwater) in Hawai'i. Elepaio 41: 75-81.

DAY, R. H. and COOPER, B. A. 1995. Patterns of Movement of Dark-rumped Petrels and Newell's Shearwters on Kauai. The Condor 97: 1011-1027. The Cooper Ornithological Society.

DEL HOYO, J.; A. ELLIOTT; and J. SARGATAL. 1992. The Handbook of the Birds of the World, Volume I. Ostrich to Ducks. Lynx Edicions, Barcelona.

ENTICOTT, J., and D. TIPLING. 1997. Photographic Handbook of the Seabirds of the World. Rev. ed. New Holland, London.

HARRIS, M. P. 1970. The biology of an endangered species, the Dark-rumped Petrel (Pterodroma phaeopygia) in the Galapagos Islands. Condor 72: 76-84.

HARRISON, C. 1990. Seabirds of Hawaii. Natural History and Conservation. Cornell University Press, Ithaca.

HARRISON, P. 1983. Seabirds - An identification Guide. Helm, Kent.

HARRISON, P. 1987. Seabirds of the World - A photographic guide. Helm, London.

HOWELL, S. N. G., and P. PYLE. 1997. Twentieth report of the California Bird Records Committee: 1994 records. West. Birds 28: 117-141.

PODOLSKY, R.; AINLEY, D.G.; SPENCER, G.; DEFOREST, L. and Nur, N. 1998. Mortality of Newell's Shearwaters caused by collisions with urban structures on Kaua'i. Colonial Waterbirds 21 (1): 20-34.

PYLE, P., L. B. SPEAR, and D. G. AINLEY. 1993. Observations of Dark-rumped Petrels off Oregon and California. Western Birds 24: 110-112.

ROBERTSON, D. and S. F. BAILEY. 1991. Cookilaria petrels in the eastern Pacific Ocean: identification and distribution. Am. Birds 45: 399-403 (Part I); 45: 1067-1081 (Part 2).

SIMONS, T. R. 1985. Biology and behavior of the endangered Hawaiian Dark-rumped Petrel. Condor 87: 229-245.

SIMONS, T. R., and C. N. HODGES. 1998. "Dark-rumped Petrel" in The Birds of North America, No. 13 (A. Poole and F. Gill, eds.). Academy Natural Sci., Philadelphia, and Amer. Ornith. Union, Washington, D. C.

SPEAR, L.B., AINLEY, D.G., NUR, N., and HOWELL, S.N.G. 1995. Population size and factors affecting at -sea distributions of four endangered procellariids in the tropical Pacific. Condor 97:613-638.

TOMKINS, R.J. and MILNE, B.J. 1991. Differences among Dark-rumped Petrel (Pteredroma phaeopygia) populations within the Galapagos Archipelago. Notornis 38:1-35.

Christian Melgar. Worthing, West Sussex, UK. 2002.

---