EXPERIMENTAL-MEASUREMENT OF NESTING SUBSTRATE PREFERENCE IN CASPIAN TERNS, STERNA-CASPIA, AND THE SUCCESSFUL COLONIZATION OF HUMAN CONSTRUCTED ISLANDS

Caspian terns, Sterna caspia, recently bred in Hamilton Harbour, at th e western end of Lake Ontario, on private property that is likely to b e developed in the next decade. To reduce this land-use conflict and t o promote the current level of biodiversity of colonial nesters in the area, artificial islands were built in the winter of 1995-1996 with d ifferent areas designated for a variety of nesting waterbirds includin g Caspian terns. In 1994, prior to island construction, we tested thre e substrate types for tern nesting preferences so that an appropriate substrate could be placed on the Caspian tern designated portion of th e new islands. We found a preference for sand over pea-gravel and crus hed stent:, and indirect evidence for a preference favouring the exper imental substrates over the pre-existing substrate of hard-packed grou nd. Based on these results, the small area of the island designed for Caspian tern nesting was surfaced with sand and was subsequently colon ised successfully. The colony established and reproduced successfully on the designated site in 1996 and grew in numbers of nesting pairs in 1997. (C) 1998 Elsevier Science Ltd. All rights reserved.