THE FOOD AND FEEDING ECOLOGY OF THE WHITE-CHINNED PETREL PROCELLARIA-AEQUINOCTIALIS AT SOUTH-GEORGIA

The diet of the white-chinned petrel at Bird Island, South Georgia was studied during chick-rearing in 1986 by quantitative analysis (by wei ght, frequency of occurrence and number of individuals) of regurgitate d or lavaged adult stomach contents. Antarctic krill comprised over 90 % of prey items and formed 47% of the diet by weight; fish and squid o ccurred in 67% and 35% of samples and formed 33% and 19% of the diet b y weight, respectively. Decapods, amphipods and salps occurred in a fe w samples. The fish were mainly lanternfish (Myctophidae) of eight spe cies (chiefly Electrona and Gymnoscopelus, forming 80% by number and 5 2% by mass of fish prey) and the nototheniid Patagonotothen guntheri ( 14% by number and 35% by mass). Of squid taken, the ommastrephid Marti alia hyadesi comprised 57% by number and 52% by mass and the gonatid G onatus antarcticus 14% by number and 42% by mass. These dietary data c onfirm white-chinned petrel as the most important avian consumer of fi sh and squid at South Georgia (and the third most important consumer o f krill). In 1986 the nototheniid fish were probably obtained via comm ercial fishing operations but the myctophids and squid were probably l ive-caught, most likely at night. Meal size increased rapidly until ch icks were three weeks old and then remained constant until the chicks were within 10 days of fledging, when it decreased. Meal delivery rate was high (one per day) for young chicks (1-10 days old) and thereafte r fluctuated between 0.56 and 0.88 meals per day until close to fledgi ng, when it was halved. These provisioning rates, and the proportion o f krill in the diet, are higher than those recorded previously at Sout h Georgia and Indian Ocean sites, probably reflecting high local avail ability of krill at South Georgia in 1986. In many respects, white-chi nned petrels at South Georgia are intermediate ecologically between pr ions and albatrosses, although specialized in their extensive consumpt ion of myctophids. Because krill and ail the main fish prey are curren tly the targets of substantial commercial fishing and the main squid p rey (Martialia) is a potential target, the ecological role and status of white-chinned petrels are of additional importance.