Nesting biology of the Sora at Vermilion, Alberta

Abstract

Nesting habitat, clutch sizes, and hatching success for 50 Sora nests in the Vermilion area of eastern Alberta are described for 1957 and 1958, two dry years on the prairies. Carex spp. alone or in association with other emergent aquatic plants were preferred nesting cover in both years, although more plant species were involved in 1958, the drier year. The mean clutch was 12.2 eggs, but hatching success declined from 80.6% in 1957 to 59.6% in 1958. Trampling by cattle and increased predation accounted for the doubled egg loss in 1958 and were attributed to increased exposure of nests through rapidly declining water levels that year. The existence of late nests suggested second attempts, but the only second nest recorded involved at least one member of a pair which had successfully hatched the first clutch. The data presented, for the nesting period only, suggests that the Sora is a successful breeding bird in this area of its range, that its high egg productivity is not affected by lower water, but that naturally declining water levels do increase egg mortality.