Reproductive responses of northern orioles to a changing food supply

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Abstract
The response of the northern oriole (Icterus galbula) to an outbreak of the forest tent caterpillar (Malacosoma disstria) on the Delta Beach Ridge, Manitoba, was studied. Orioles responded in 1976 to the increased food supply by feeding on all life stages of the insect and by feeding late instar larvae and pupae to their young. The nesting density doubled in 1977, the 2nd year of the 2-year outbreak, but the caterpillar larvae died off before the orioles' chick-rearing period. The 1978 breeding density was back down to the level of 1976. Clutch sizes and body weights did not change despite the increase and eventual reduction in both food abundance and nesting density. Productivity was lower, and hatching failure and nestling death were higher, at the higher nesting density.