Coulter, Malcolm C.

Duffy, David Cameron

Harcourt, Sylvia A.

Aquatic Commons

STATUS OF THE DARK-RUMPED PETREL ON ISLA SANTA CRUZ, 1981 
by 
Malcolm C. Coulter, David C. Duffy & Sylvia Harcourt 
The Dark-rumped Petrel, Pterodroma phaeopygia, is a gull-sized seabird that breeds only in the Hawaiian 
and Galapagos archipelagos. The populations in both areas have been declining for many years. On Santa 
Cruz 4 colonies have been visited yearly since 1978. We visited these colonies in early August, 1981, and 
compare our figures with those of previous years. 
In the Galapagos this petrel breeds in the highlands on 4 islands: Santa Cruz, Fioreana, Santiago and San 
Cristobal. It may also breed on Isabela, though no nests have been found there. Time of breeding varies 
from place to place. On Santa Cruz, birds return in May; eggs are laid in June and July. Each pair lays a 
single egg in an underground burrow. The eggs are incubated for 50 days and the young remain in the 
burrow for an additional 110 days (Harris, M.P. 1970. The biology of an endangered species, the Dark-
rumped Petrel (Pterodroma phaeophygia), in the Galapagos Islands. Condor 72: 76-84). Breeding lasts 5 to 
6 months. 
At Media Luna on Santa Cruz 4 colonies, 'Mike's', 'Corner', 'Creek' and 'Gully', were visited in 1978, 
1979 and 1980 by R.J. Tomkins, R. Baker and F. Bass. In these years they found 63,38 and 32 burrows that 
were occupied by birds. In 1981 we found 18 active burrows of which 7 had eggs. This represents a decline 
in number of active burrowll by 44% since 1980 and 71 % since 1978, with an average yearly decline of 33%. 
At this rate the population will decline to 10% of the 1978 size by 1984 and to 1 % by 1990. If nothing is 
done to protect the bird, these populations will become extinct within the next 10 to 15 years. 
The main cause of this decline is predation by feral animals on eggs and young, and to a lesser extent on 
adults. We are presently establishing a program of feral animal control to reduce this predation. 
Dark-rumped or Hawaiian Petrel Drawing by M. Estey 
24 
Noticias de Galapagos, no. 35 1982


Status of the Dark-rumped Petrel on Isla Santa Cruz, 1981

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Status of the Dark-rumped Petrel on Isla Santa Cruz, 1981

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