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. Résumé : Le havre de Hamilton, situé à l'extrémité ouest du lac Ontario, héberge des colonies reproductrices de six oiseaux aquatiques piscivores : le cormoran à aigrettes (Phalacrocorax auritus), le bihoreau gris (Nycticorax nycticorax), le goéland argenté (Larus argentatus), le goéland à bec cerclé (Larus delawarensis), la sterne pierregarin (Sterna hirundo) et la sterne caspienne (Sterna caspia). Chez toutes ces espèces, la plupart des couples de reproducteurs nichent sur la terre ferme, sur des terrains privés soumis à de multiples activités industrielles ou travaux d'aménagement. La construction de trois îles artificielles dans le bassin est du havre, à l hiver 1995-1996, est une occasion d'atténuer le conflit qui touche en ce moment l'utilisation des terres et de préserver en même temps la diversité actuelle de la faune ailée. Nous avons donc utilisé les données écologiques pour déterminer quels substrats et quels types de végétation conviennent à la nidification, afin de répondre aux préférences des oiseaux aquatiques et de faciliter l'occupation des êles par ceux-ci. Nos recommandations en matière de conception et de gestion des habitats privilégient les techniques qui permettent d'éviter le déplacement des deux espèces de sternes par le goéland à bec cerclé et du bihoreau gris par le cormoran à aigrettes. Nous proposons un mécanisme de gestion à long terme fondé sur les divers aspects de la biologie des oiseaux et sur les interactions écologiques connues entre les diverses espèces. [Traduit par la Rédaction]
Evidence from colony surveys and local Inuit knowledge strongly suggest that the Canadian population of ivory gulls (Pagophila eburnea) has declined dramatically. The observations of ivory gulls at sea presented here are consistent with this. Ivory gulls were observed during two cruises on the Russian icebreaker Kapitan Khlebnikov in the eastern Canadian high Arctic in August 1993 and 2002. Ivory gulls were seen 3.5 times more often in 1993 (n = 176) than in 2002 (n = 149), and, corrected for observation effort, four times more ivory gulls were seen in 1993 than in 2002. Ivory gulls are scavengers: they were never observed feeding on fish behind the vessel while ice-breaking, although black-legged kittiwakes (Rissa tridactyla) often were seen feeding in this way. Ivory gulls were observed scavenging around polar-bear (Ursus maritimus) kills in 1993 but not in 2002. By far the largest number of ivory gulls was seen near Grise Fiord in 1993. There, opportunities for them to scavenge were likely good at the community landfill as well as at Inuit and polar-bear kills due to complete ice coverage of the surrounding marine area. No ivory gulls were seen there in 2002. Observations of four individuals in 1993 and five individuals in 2002 near the southern end of Eureka Sound and in Norwegian Bay, 150 km from the nearest known breeding colonies, suggest that as yet undiscovered colonies might exist in this area. With three lines of evidence (colony surveys, local Inuit knowledge, at-sea surveys) now indicating population decline, urgent reassessment of the status of ivory gulls in Canada needs to take place.
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