Food of Nestling Yellow-Headed Blackbirds, Cariboo Parklands, British Columbia

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Abstract
In June of 1963 and 1964 food samples were taken from nestling yellow-headed blackbirds in the Cariboo Parklands, British Columbia, by placing segments of pipe cleaners around their necks tightly enough to prevent swallowing of the food. Weather was fair and warm in 1963 but cold and rainy in 1964. Damselflies (Enallagma) were the most important food items at Rush Lake, a lake of high productivity, but Diptera comprised 96% of the food at Westwick Lake, a lake of lower productivity. Nestling survival was better during the warm, dry weather of 1963, and mortality was proportionally higher at Westwick Lake than at Rush Lake in 1964. In the Cariboo, yellow-headed blackbirds are restricted to lakes of higher productivity than redwinged blackbirds, and the available evidence indicates that survival of young is better on the more productive lakes. At Rush Lake the diversity of the food samples was greatest in the late-afternoon, intermediate in the early-morning, and lowest in the mid-day samples when damsel-flies constituted over 90% of all prey items. Correlated with the morning emergence of metamorphosing damselflies, naiads and tenerals were proportionally more common in the mid-day samples, and adults were proportionally more common in the late-afternoon samples. The data are consistent with the hypothesis that the adult blackbirds foraged more in the grasland erly in the morning than later in the day and turned to smaller insects primarily late in the afternoon when damselflies were harder to catch.