Abstract
1) Breeding biology of Leach's Storm-petrels Oceanodroma leucorhoa was studied On Daikoku Island(42°52'N, 144°52'E), Akkeshi, Hokkaido, between late April and late October, 1982. 2) Breeding parameters were the following: incubation period, 41.8 days; incubation spell, 2.9 days; chick growth rate (K), 0.078; chick asymptotic weight, 69g; fledging weight, 58.3g; fledging period, 61.2 days; adult weight, 48.5g; egg weight, 11.2g. 3) Chick survival rate was 92% in average. Nesting habitat, burrow depth, laying date and nearest nest distance did not influence chick survival. 4) Hatching success was 75% in average. Hatching success of eggs in deep burrows was higher than those in shallow ones. Early laid eggs had higher hatching success than late laid ones. 5) The petrels made deep burrow nests under Calamagrostis with complex root systems in which hatching success was high. 6) Hatching success was higher in the following order: Calamagrostis >Artemisia-Urtica>Petasites-Polygonum. However, habitat preference shown by burrow density was in the order, Artemisia-Urtica (1.69/m2)>Calamagrostis (0.80/m2)>Petasites-Polygonum (0.60/m2). 7) The petrel in suitable habitat (Calamagrostis) laid earlier than in less suitable habitats. This partly supports "Density limiting model" (Davies 1978).
