Digestion of Spruce Budworm Larvae and Pupae in the Olive-backed Thrush, Hylochichla ustulata swainsoni (Tschudi)

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Abstract
To use gizzard analysis quantitatively, in the assessment of bird predation on insect populations, information is needed on the time that identifiable remains of the prey can be found in the gizzard and on the rate at which these remains disappear. The digestion rate, measured by the disappearance of mandibles or cremasters, has been studied for larvae and pupae of the spruce budworm, Choristoneura fumiferana (Clem.), when eaten by the olive-backed thrush, Hylocichla ustulata swainsoni (Tschudi).