Ardea
Official journal of the Netherlands Ornithologists' Union

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James P.C. & Verbeek N.A.M. (1984) Temporal and energetic aspects of food storage in Northwestern Crows. ARDEA 72 (2): 207-215
Temporal and energetic aspects of the food storage behaviour of the North-western Crow Corvus caurinus were investigated on Mitlenatch Island, B.C., Canada. Crows stored predominately marine intertidal food, especially clams, crabs, fish and worms, on the hillsides surrounding the intertidal beach. They also carried food to other parts of the island, presumably to be stored. Food was stored at low tide, and recovered at high tide. Most food was stored in May and June. This seems to be a result of a relative scarcity of non-intertidal food at high tide earlier in the season. During this period too, females are forming and laying eggs, and may depend on stored food at high tide. An experiment confirmed that food stored at low tide was important to an incubating female during high tide, as removal of the stored food caused a significant decline in her nest attentiveness. Overall, food was stored equally in the morning and afternoon, but clams were stored mostly in the morning. Food recoveries occurred mostly in the afternoon. More food was stored on falling than on rising tides, and vice versa for recoveries. The mean tidal height for food recoveries was significantly higher than that for food storages. A combined hourly tide time analysis illustrates these patterns. The crow's storage strategy appears to be a short-term tidal one. The energetics. of clam storage was studied. Clam sizes were derived through an indirect method involving collection of double shells. Caloric value of clams was determined by bomb calorimetry, and used to predict the amount of food needed by a crow at high tide. This was compared to observed data. Finally, the profitability of clam storage was investigated, and compared to a similar analysis done on the whelk-dropping behaviour of the species.


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