Design and management of bird nesting habitat: tactics for conserving colonial waterbird biodiversity on artificial islands in Hamilton Harbour, Ontario

Hamilton Harbour, at the west end of Lake Ontario, supports breeding colonies of six piscivorous waterbirds: double-crested cormorant (Phalacrocorax auritus), black-crowned night-heron (Nycticorax nycticorax), herring gull (Larus argentatus), ring-billed gull ( Larus delawarensis), common tern (Sterna hirundo), and Caspian tern (Sterna caspia). Most breeding pairs of all species nest on privately owned mainland locations that are subject to multiple industrial and development activities. The construction of three artificial islands in the eastern basin of Hamilton Harbour in the winter of 1995-1996 presents an opportunity to simultaneously reduce current land-use conflict and maintain the existing avian biodiversity. Accordingly, we used ecological information to determine suitable substrates and vegetation to satisfy nesting habitat preferences and to facilitate the occupation of the islands by nesting waterbirds. Our recommendations for habitat design and management emphasize techniques to prevent displacement of both tern species by ring-billed gulls and of night-herons by cormorants. We propose long-term management procedures based on aspects of the biology and known ecological interactions among the various species. Resume : Le havre de Hamilton, situe a l'extremite ouest du lac Ontario, heberge des colonies reproductrices de six oiseaux aquatiques piscivores : le cormoran a aigrettes ( Phalacrocorax auritus), le bihoreau gris (Nycticorax nycticorax), le goeland argente (Larus argentatus), le goeland a bec cercle (Larus delawarensis), la sterne pierregarin ( Sterna hirundo) et la sterne caspienne (Sterna caspia). Chez toutes ces especes, la plupart des couples de reproducteurs nichent sur la terre ferme, sur des terrains prives soumis a de multiples activites industrielles ou travaux d'amenagement. La construction de trois iles