New Zealand Journal of Marine and Freshwater Research abstracts

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Foraging responses of stilts {Himantopus spp.: Aves) to changes in behaviour and abundance of their riverbed prey

RAYMOND J. PIERCE*

Department of Zoology University of Otago P. O. Box 56, Dunedin New Zealand

Abstract Riverbed foraging by pied stilts (Himantopus h. leucocephalus) and the endangered black stilt (H. novaezealandiae) was studied in the Cass River Valley, South Island, New Zealand. The staple riverbed diet of both species was aquatic larvae of Deleatidium spp. (Ephemeroptera), usually captured by pecking. When the larvae were inactive and hidden from view, particularly when the water temperature was below 5°C, black stilts used the non-visual methods of probing or raking in the gravel to find food. Pied stilts did not use non-visual methods and so were forced to feed at a low rate or move to other temporarily more profitable habitats. Black stilts foraged mainly at the riffles where prey was most abundant, whereas pied stilts foraged mainly at pools where prey was less common but more easily seen. During the emergence drift of Deleatidium, both species of stilts switched from feeding on larvae to feeding on drifting subimagines.

Keywords Himantopus h. leucocephalus; H. novaezealandiae; foraging responses; riverbed; mayfly; Deleatidium; prey behaviour; stilts; food

New Zealand Journal of Marine and Freshwater Research, 1986, Vol. 20: 17-28 1986Received 27 November 1984; accepted 4 July 1985

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