Shorebird avoidance of nearshore feeding and roosting areas at night correlates with presence of a nocturnal avian predator
73 – 76
1 April 06
Theunis Piersma, Robert E. Gill, Petra de Goeij, Anne Dekinga, Marnie L. Shepherd, Daniel Ruthrauff, Lee Tibbitts
Department of Marine Ecology and Evolution, Royal Netherlands Institute for Sea Research (NIOZ), PO Box 59, 1790 AB Den Burg, Texel, The Netherlands.
We here report two anecdotes about avian interactions relevant to the interpretation of differences in shorebird habitat use between day and night. Several studies have reported that shorebirds avoid feeding and roosting along nearshore areas at night yet commonly use these sites during daytime. This suggests that nighttime avoidance of nearshore places is a response to increased danger of predation. When mist-netting during autumn 2005 on nearshore intertidal habitats along South Spit, Egegik Bay (Alaska Peninsula), Alaska, we discovered that shorebirds that occurred there in large numbers during daytime low tides and roosted there during day-time high tides (especially Dunlin Calidris alpina, Rock Sandpipers Calidris ptilocnemis, Black-bellied Plover Pluvialis squatarola, and Surfbirds Aphriza virgata), were absent at night. Their avoidance of the area correlated with Short-eared Owls Asio flammeus concurrently hunting over the beach and adjacent intertidal habitats. Spotlighting over nearby expansive intertidal mudflats confirmed that the same suite of species continued to forage or roost nearby at night. To bring the story full circle, the morning following one mist-netting effort we found a Short-eared Owl on the beach that had been killed earlier by a Gyrfalcon Falco rusticolus. In the owl’s stomach were remains of a freshly devoured Dunlin.