Spacing behavior of visual- and tactile-feeding shorebirds in mixed-species groups

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Abstract
Time activity budgets were determined for tactile-feeding Long-billed Dowitchers (Limnodromus scolopaceus) and Pectoral Sandpipers (Calidris melanotus), and for visual-feeding Lesser Yellowlegs (Tringa flavipes) and Semipalmated Sandpipers (Calidris pusilla) while these species were foraging in mixed-species groups at Inuvik, Northwest Territories. Pectoral Sandpipers and Lesser Yellowlegs spent the most time vigilant. Intraspecific aggressive interactions were relatively common among Pectoral Sandpipers and were less frequent in the other species. The intensity of aggressive attacks was higher in visual-feeding than in tactile-feeding species. Tactile-feeding species were often with conspecifics and visual-feeding species were usually alone. If aggression is a proximate mechanism in spacing these shorebirds, intensity, not frequency, appears to be most important.