Habitat utilization and breeding success of Leach's storm-petrel, Oceanodroma leucorhoa

Abstract

It is generally assumed that individual organisms behave optimally. In terms of habitat utilization, die optimal habitat for any species is that which provides the optimum conditions for survival and reproduction. -- This study compared how Leach's Storm-Petrels, Oceanodroma leucorhoa, utilized forest and open habitat on Great Island, Newfoundland. Specifically, nesting habitats were compared in terms of slope, aspect, and peat compaction. The adaptive significance of habitat utilization was assessed through comparisons of burrow density, the proportions of active and occupied burrows, hatching success, chick growth, breeding success and predation risk. -- Forest and open habitats differed; open habitat had steeper slope and more compact soil than forest, which had deeper peat. Burrow density and activity were greater in forest than open habitat, indicating that Leach's Storm-Petrels actively selected forest over open habitat Clearly, based on area, forest habitat supported a greater number of breeding pairs. Moreover, birds nesting in forest exhibited greater hatching and breeding success than birds nesting in open habitat, thus storm-petrels nesting in forest were disproportionately more productive than storm-petrels nesting in open habitat. -- Avian predation of Leach's Storm-Petrels did not differ between forest and open habitats, but varied seasonally in both. Predation was much reduced in both habitats following the inshore movement of spawning Capelin, Mallotus villosis. -- The terrestrial flora of the habitats utilized by Leach's Storm-Petrels change over time, being influenced by other seabirds (e.g. gulls and puffins on Great Island). Forest habitat is estimated to have decreased by 17 % on Great Island over the past 25 years. Open habitat has been expanding, which will negatively affect the overall productivity of the Leach's Storm-Petrel colony. Generalizations to other Leach's Stonn-Petrel colonies in the northwest Atlantic are also made.