NESTING AND FOOD-HABITS OF THE FLAMMULATED OWL (OTUS-FLAMMEOLUS) IN SOUTH-CENTRAL IDAHO

Flammulated owls (Otus flammeolus) arrived at our 25-km(2) study area in Idaho from mid- to late May 1991-94. Twenty-four nesting pairs util ized 22 nesting cavities. Twenty (83%) of the nests were in dead trees and four (17%) in live trees. Thirteen (54%) nests were in broken-top Douglas-fir (Pseudotsuga menziesii) snags, and 11 (46%) were in tremb ling aspen (Populus tremuloides). Mean diameter at breast height of 13 nest trees was 49.9 cm (SD = 18.9), while mean cavity height was 5.1 m (SD = 0.6). Mean entrance diameter for 11 nests was 6.8 cm (SD = 1.3 ). Mean hatching date at 11 of the 24 nests was 26 June (range, 12 Jun e through 11 July) and mean fledging date was 18 July (range, 7 July t hrough 2 August). Mean brood size for nine nests was 2.3 (range, 2-3) young per nest. Nightly food deliveries at nest sites peaked within th e 2-hr period after dark and before daylight. Mean number of nest visi ts by adults during the nesting stage was 93. Although lepidopterans c omprised 79% and orthopterans 0.3% of the available prey within the st udy area in 1992, 65 food deliveries at one nest revealed 43.1% orthop teran and 9.2% lepidopteran prey. At other nest sites, lepidopterans w ere the prominent prey. Four banded owls returned to the same territor y for two, three, and four consecutive nesting seasons.