There are two sub-species of grey–faced petrel, macroptera, which breeds on islands in the Atlantic and Indian oceans and off southwestern Australia, and gouldii, which breeds on off shore islands and coastal headlands of the northern North Island of New Zealand.
The birds visit their burrows after dusk and leave again before dawn. They start to breed from 6 to 7 years of age. The petrels visit their colonies between March and April to clean out their burrows and take part in pair bonding. Egg laying starts from late June to the end of July, one white egg is laid. The egg hatches after 51 – 58 days of incubation.
Both parents help in incubation and after the chick hatches the parent guards the chick for the first few days. The chick is then left on its own and is visited every few days with food, sometimes this may mean a wait of 7 days or more before its next feed. The parent has to travel many miles from their burrows in search of food, which is regurgitated for the chick. This may include squid, fish and crustaceans. The chick continues to grow and fledging takes place from early December to the end of January. The moult of the adult birds, take place from January to April.
The largest breeding colony of grey-faced petrel is on Whale Island, Moutohora, near Whakatane in the eastern Bay of Plenty. There are also small colonies on the mainland near Whakatane but these colonies are very fragile.
In the breeding season of the year 2000 a study was being done on one of the mainland colonies near Whakatane by Phillipa Gardner of grey–faced petrels, using a safety door on their burrows. This was a trial for the protection of petrels that are at risk from predators eating their chick or egg.
Unfortunately a high percentage of the chicks in the study were taken illegally for food. These birds are protected by law, and illegal harvesting will see these fragile colonies die out. If the chicks are taken then there will be no replacement egg laid. This in time will mean that once the parents die, no new adult offspring will be replacing them. The birds taken would have weighed no more than 300g and with the feathers and head removed probably weighed no more than 150g.
On a recent trip to Whale Island in December, the petrels could be seen just before dusk gathering off the island. The birds were coming back to feed the young that were nearly due to fledge. As dusk fell, birds would skim over the island looking for their burrows, they then crash through the trees and head for their nest site. Sometimes they liked to sit before going underground. Some birds get caught in the trees as they crash through and die.
Whale Island was once home to goats, rats, and rabbits. The Wildlife Service, and then the Department of Conservation eradicated these pests. It is vital that our islands are kept free of predators and that bait stations are monitored. It will only take one rat or stoat to undo all the work of the previous years.
In April and May, and at other times, the birds can be heard calling during the night over Ohope and Otarawairere in Whakatane. One colony at Ohope is against the hillside and on occasions birds crash into new homes that were not there the previous nesting season. It must be quite a shock for the birds to suddenly find something blocking their flight path to their burrows.
The grey–faced petrels have many predators including — stoats, rats, dogs, illegal harvesting, fire, birds of prey. By visiting their colonies at night they do not run the risk of being harassed by birds of prey.
Every year young fledgling grey–faced petrels are brought into Whakatane bird rescue, as instead of heading out to sea the birds get disorientated and land in town. Sometimes heading for the lights of night industry such as the Kawerau paper mills. Once checked out most of the birds can be released in the evening. Some years more birds are brought in, this maybe due to the cloudy conditions, no moon or stars to guide them, or wind conditions. Strong northerly winds will send the birds towards Whakatane instead of heading out to sea.
Rats on Whale Island, Moutohora
Norway rats Rattus norvegicus, were present on Whale Island between about 1920–1987. During 1969–71 they reduced by less than 10 — 35% the breeding success of grey–faced petrel by eating unattended eggs and killing young or weak chicks. Rabbits, Oryctolagus cuniculus, introduced to Whalwe Island, 240ha surface area, in about 1968, multiplied rapidly to reach a density of up to 375 individuals/ha by early 1973. Their young and corpses were also eaten by rats and this additional food, available when petrels were absent or less vulnerable, February-June, increased the rat population. During 1972 to 1977, production of fledged young petrels was negligible. Application of anticoagulant baits to kill rats in 1978, 1980 and 1982 resulted in large numbers of young petrels fledglings only in those years; there was no carry–over effect in following years. Island–wide laying by hand of brodifacoum baits, Talon 50WB, in 1985 decimated the rat population. Further poisoning, associated with tandem operation to kill rabbits, led to the eradication of both mammals by late 1987. Breeding success of the petrels from 1985 to 1988 (no data for 1989) and from 1990 to 1994, was consistent and increasing.
The first indication that the petrel population was under stress was in 1962, when muttonbirders, local people of Maori decent with hereditary rights to kill for food the young petrels before they fledge, concerned at the scarcity of petrel chicks for exploitation, requested a ban on the harvest, rahui in 1963 and 1964. Wildlife Refuge status imposed on Moutohora in 1964 has legally protected the petrels since then.
Other common names: —
North island muttonbird, great-winged petrel.
41 cm., 550 g., plumage black brown, pale grey face and throat, bill, legs and feet black.
Where to find: —
The main colonies are on Hen, Mokohinaus, the Mercury and Alderman, Whale and White Islands.
Credit for the photograph: —
Illustration description: —
Godman, Frederick du Cane, Monograph of the Petrels, 1907-1910.
Heather, B., & Robertson, H., Field Guide to the Birds of New Zealand, 2000.
Marchant & Higgins, 1993.
Oliver, W.R.B. New Zealand Birds, 1955.
Imber, Mike, Harrison, Malcolm, and Harrison, Jan, New Zealand Journal of Ecology (2000) 24 (2); 153-164.
Page date & version: —
Thursday, 29 May 2014; ver2009v1