ABSTRACT. At ice edges in the Canadian High Arctic, seabirds and marine mammals eat arctic cod (Boreogadus saida) and, to a lesser extent, zooplankton (calanoid copepods and Parathemisto) and ice-associated amphipods. Cod eat ice-associated amphipods, other ice-associated taxa (harpacticoid and cyclopoid copepods), and zooplankton. Calanoid copepods, Parathemisto, and the ice-associated amphipods studied (Onisirnus glacialis, Apherusa glacialis, Gammarus wilkitzkii) all eat primarily diatom algae characteristic of the under-ice flora. From this information, a food web at the ice edge is constructed. Key words: trophic relationships, arctic, ice edges, seabirds, marine mammals, cod, epontic community, zooplankton RÉSUMÉ. En bordure des glaces dans l'Arctique polaire canadien, les oiseaux de mer et les mammifkres marins se nourissent de morue arctiques (Eoreogadus saida) et, quoique dans une moindre mesure, de zooplanctons (coptpodes calanoides et Parathemisto) et d'amphipodes associés ?t la glace. La morue se noumt d'amphipodes ainsi que d'autres taxons (copepodes harpacticoides et cyclopes) tous associes ii la glace, et de zooplancton. Les copdpodes calanoides Parathemisto, et les amphipodes associes ii la glace qui ont et6 ttudiks (Onisimus glacialis, Apherusa glacialis, Gammarus wilkitzkii) tirent tous leur substance principale d'une algue diatomke commune il. la flore trouvee sous la glace. A partir de cette information, une chaine alimentaire est donc construite pour la bordure des glaces.Traduit par Pierre Bibeau, Arkéos Inc., Montréal.

From 5 June to 4 July 1976, I collected 98 thick-billed murres (Uria lomvia) and 47 black guillemots (Cepphus grylle) at ice edges in Barrow Strait, N.W.T., for diet studies. Alcids were collected at coastal ice edges and at the edges of landfast ice farther offshore; in both habitats food availability was also studied. At coastal ice edges, murre diet was dominated by Arctic cod (Boreogadus saida, 14% of dry weight biomass) and the amphipod Onisimus litoralis (18%); guillemot diet was dominated by cod (99%), decapods (0.4%), and amphipods (0.2%). At offshore ice edges murres took cod (96%), Parathemisto (2%), and Onisimus glacialis (2%); guillemots took cod (54%), O. glacialis (35%), and Apherusa glacialis (5%). Morisita's overlap values showed that diets of these two alcids were more similar at offshore than at coastal ice edges and that there were considerable habitat-related differences in diet. Data on food availability suggested that at offshore ice edges, murres were feeding in the water column and at the undersurface of the landfast ice; guillemots fed almost solely at the ice undersurface. At coastal ice edges, both alcids were probably feeding at the ice undersurface and on the sea bottom; in addition, murres fed in the water column. The importance of epontic (= ice-associated) fauna in the diets of alcids during spring is discussed.

We examined the effects of patch size, local forest cover, and regional forest cover on the numbers and species composition of forest birds detected during fixed-radius point counts in 287 forest patches in four replicate study areas in southern Ontario. Each study area consisted of two subareas differing in regional forest cover. The number of forest-interior species (as classified from the literature) detected per count, after controlling for forest patch size, tended to be higher in subareas with greater regional forest cover, but this effect was much stronger in some study areas than others. In contrast, numbers of edge species and interior-edge generalists were higher in subareas with lower regional forest cover. Within study areas, the number of forest-interior species increased and edge species decreased with both woodlot size and core area (amount of forest >100 m from an edge), but total species diversity at a point was relatively unaffected. Analyses of individual species generally corroborated the patterns, except that some so-called interior-edge generalists were more likely to be detected in large woodlots, while others were more likely in small woodlots. There was a tendency for the loss of forest-interior species with decreasing woodlot size to be greatest in subareas with low regional forest cover. In the context of highly fragmented landscapes such as southern Ontario, where many forest-dependent species have become rare, forest conservation should focus on protecting or restoring larger forest tracts in areas with substantial remaining regional forest cover. Efectos del Contexto del Paisaje y la Fragmentación sobre Aves de Bosque en el Sur de Ontario Resumen.  Examinamos el efecto del tamaño de parches y de la cobertura de bosque a escalas local y regional sobre el número y composición de especies de aves de bosque. Las aves fueron detectadas mediante puntos de conteo de radio fijo en 287 parches de bosque, en cuatro áreas de estudio replicadas en el sur de Ontario. Cada área de estudio consistió en dos sub-áreas, las que se diferenciaron en la cantidad de cobertura regional de bosque. Luego de controlar por el área de los parches, el número de especies de interior de bosque (clasificadas según la literatura) detectadas por conteo tendió a ser mayor en sub-áreas con mayor cobertura regional de bosque. Sin embargo, este efecto fue mucho mayor en algunas áreas de estudio que en otras. En contraste, los números de especies de borde y especies generalistas de borde-interior fueron mayores en las sub-áreas con menor cobertura regional de bosque. Dentro de cada área de estudio, el número de especies de interior de bosque aumentó y el número de especies de borde disminuyó con el aumento del tamaño y del área nucleo (cantidad de bosque a >100 m del borde) de los fragmentos de bosque, pero la diversidad total de especies en un punto no se vió relativamente afectada. Los análisis individuales por especie corroboraron los patrones observados, exceptuando que alguna especies llamadas generalistas de borde-interior tuvieron una mayor probabilidad de ser detectadas en fragmentos grandes, mientras que otras tuvieron mayor probabilidad en fragmentos pequeños. La tendencia más marcada a perder especies de interior de bosque con la reducción del área de los fragmentos ocurrió en las sub-áreas con baja cobertura regional de bosque. En paisajes en un contexto altamente fragmentado tales como en el sur de Ontario, donde muchas especies dependientes de bosque se han tornado escasas, la conservación de bosques debiera estar enfocada a la protección o restauración de grandes extenciones de bosque en áreas donde la cobertura regional de bosque es aún substancial.

ABSTRACT. In 1979, 17 species of birds were seen during studies near the Pond Inlet ice edge. Northern fulmars (Fulmurus glacialis), black-legged kittiwakes (Rissu triductylu), thick-billed murres (Uriu Zomvia), and black guillemots (Cepphus grylle) all avoided the ice edge when bordered with heavy pack ice and all but kittiwake used the ice edge primarily for feeding. Guillemots and fulmars occurred in highest numbers in water along rough and moderately rough landfast ice; murres and kittiwakes showed no preference for such areas or for the other habitat surveyed (smooth landfast ice). Narwhals (Monodon monoceros), white whales (Delphinapterus leltcas), and ringed seals (Phoca hispidu) were the only marine mammals common at the ice edge. Whales repeatedly dived under the edge -probably feeding, searching for open water west of the ice edge, or both. Densities of seals near the ice edge were higher than elsewhere on landfast ice.Divers observed arctic cod (Eoreogadus suidu) close to the undersurface of landfast ice. Fish offshore were generally smaller, younger, and smaller-at-age than those inshore. Offshore, arctic cod were more numerous in areas with a rough under-ice surface than under smooth ice. Cod concentrated in crevices within rough under-ice surfaces. Inshore, cod were captured from ice cracks over shallow water.I conclude that vertebrates occur at ice edges for one or more of several reasons. Ringed seals and arctic cod live in close association with landfast ice; they probably occur near ice edges simply because landfast ice is present there. Ice edges seem to be primarily barriers against the further movements of whales toward summering locations. Finally, for murres and some other birds, ice edges seem to be favored feeding locations (relative to open sea conditions) due to greater access to preferred foods.Key words: arctic seabirds, ringed seal, narwhal, arctic cod, ice edges, Pond Inlet, habitat use, behavior, arctic waters, Lancaster Sound, Baffh Bay R~S U M É . En 1979, dix-sept (17) esp&ces d'oiseaux ont kté aperçues durant des etudes il proximite du bord de laglace 9 Pond Inlet. Les fulmars boreaux (Fulmurus ghciulis), les mouettes tridactyles (Rissa tridactylu), les marmettes de Briinnich (Uriu lomviu) et les guillemots noirs (Cepphus grylle) Bvitaient tous le bord de la glace quand celui-ci etait borde par le pack tpais et tous, sauf la mouette, utilisaient le bord de la glace pour se nourrir. Les guillemots et les fulmars apparaissaient en plus grand nombre dans l'eau longeant la banquise continue qui prksentait une surface rugueuse ou moderke. Les marmettes et les mouettes n'ont demontre aucune preference pour de telles zones ou pour d'autres habitats identifies lors de la reconnaissance (banquise continue B surface unie).Les narvals (Monodon monoceros), les belugas (Delphinapterus leucus) et les phoques annelés (Phocu hispidu) etaient les seuls mammifhres marins B être frdquemment en bordure de la glace. Les baleines nageaient continuellement sous la bordure de la glace, soit pour se n...

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