Crossbill foraging behavior, bill structure, and patterns of food profitability

摘要: The rate at which White-winged Crossbills (Loxia leucoptera) and Red Cross- bills (L. curvirostru) extract consume seeds from conifer cones was measured in the laboratory. were more efficient than handling small seeds, but converse found for large seeds. Time required to (interseed interval) depended on stage of cone ripeness usually greater seed-husking time. Interseed intervals greatest, intake rates (mg kernel ingested/set) lowest, when closed or they open, had shed most their seed. foraging spruce (Picea spp.) open full while pine (Pinus difficult between scales. differences efficiency related morphological two species; have slender, shallower, less powerful do Crossbills. are consistent with patterns crossbill distribution use field. Differences bill structure may be increasing during periods food limitation. among individual crossbills hypothesis that variation individuals should birds forage foods used greatest limitation stressful times. Received 7 Nov. 1986, accepted