Variation in Chick Provisioning of Streaked Shearwaters (Calonectris leucomelas) during the Early Nestling Stage

We examined chick provisioning rates of Streaked Shearwaters (Calonectris leucomelas) breeding on Sasudo Island, Korea for one to 18 chick-days. Adults remained with their chick for four days on average (range=1-6) after hatching, and foraging trip duration was 1.2±0.6 days. Nightly feed mass during brooding increased with chick age, but the total mass of food delivered to chicks was not increased through additional feedings during the day, most of which took place soon after hatching. Feed mass was smaller during brooding (31g) than early chick rearing (mean=40g), but the mass of food carried by brooding adults (mean=57g, n=22) was larger, and was allocated to feeding the chick (28g) and to their own maintenance (29g). When chicks were fed twice in the same night during chick rearing, they accepted less food from the second parent (mean=31g) than from the first (38g). However, the mass of feeds only fed once at night increased with chick age, implying that although the chicks did not eat all of the food presented by both parents at night, the chick's gut capacity and feed mass increased with chick growth. Overall, 91% of chicks were fed at least once per night with 1.2±0.6 feeds per day, and were fed less during brooding (0.8±0.4) than during chick rearing (1.3±0.6). Throughout the study period, parents probably adapted their provisioning rates according to the increase of the chick's demand, which may be represented by the chick's gut capacity.