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The hypothesis that northern resident killer whales (Orcinus orca) move in response to the seasonal availability of salmon (Oncorhynchus spp.) was tested using sightings and acoustic recordings of whales and data on the timing and abundance of salmon in Johnstone Strait, off Vancouver Island, between 1984 and 1988, and from King Island, on the central British Columbia coast, for a 2-month period in 1989. Whales were most abundant in Johnstone Strait between July and October when salmon migrate through the strait. Individual whales seen in the strait during summer were observed around King Island in spring 1989, coinciding with local sockeye and chinook salmon runs. In Johnstone Strait during summer 1988, whales foraged along the shore and in areas of strong current, where salmon occur in high densities. However, less than half of the 16 pods in the northern resident community were present on more than 15% of summer days (1984–1988). The occurrence of 6 pods (A1, A4, A5, C1, D1, and H1) in Johnstone Strait during summer was positively and significantly associated with sockeye and pink salmon abundance, whereas pod G1 was positively and significantly associated with chum salmon. Although we demonstrate an association between certain pods and certain salmon species, we cannot determine whether this reflects the true preference of pods or represents differences in the whales' arrival times in Johnstone Strait that are related to other factors. Our data suggest that within the northern resident community, pods may have seasonal ranges.

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Using a population of Dall's sheep (Ovis dalli dalli), we examined two of the four main sexual-segregation hypotheses proposed: (1) the reproductive-strategy hypothesis, which proposes that males feed in the best foraging areas to enhance their reproductive fitness and females use areas with lower predation risk to raise offspring; and (2) the sexual dimorphism -body size hypothesis, which proposes that females use the areas with best forage to satisfy the nutritional demands of gestation and lactation, and that males, owing to their larger body size, have greater absolute metabolic requirements and therefore have to feed on forages which are more abundant but of lower quality. In our study, males were found farther from cover, in gentle terrain, and at lower altitude than were female groups, which were near cliffs or talus at higher altitudes. Female groups without lambs left cover, but were always active (feeding or moving). Forage density index values were higher in areas used by males than in areas used by female groups. Nutritional components were generally similar, but fibre content was higher in male areas. Signs of wolves (Canis lupus) and predation on Dall's sheep were recorded only at male areas. The results support the reproductivestrategy hypothesis, indicating that predation plays a key role in the development of sexual segregation in Dall's sheep.Résumé : Nous avons examiné, chez une population de mouflons de Dall (Ovis dalli dalli), deux des quatre principales hypothèses proposées pour expliquer la ségrégation sexuelle : (1) l'hypothèse de la stratégie reproductive qui veut que les mâles utilisent les meilleurs sites de recherche de nourriture pour augmenter leur fitness reproducteur, alors que les femelles choisissent des régions avec un plus faible risque de prédation pour l'élevage de leurs petits et (2) l'hypothèse du dimorphisme sexuel et de la taille du corps, selon laquelle les femelles utilisent les meilleurs sites de recherche de nourriture pour rencontrer les besoins nutritionnels imposés par la gestation et l'allaitement, alors que les mâles, qui ont des exigences métaboliques plus grandes à cause de leur taille plus importante, doivent se contenter de sources de nourriture qui sont plus abondantes, mais de qualité inférieure. Dans notre étude, les mâles se retrouvaient plus loin des zones de refuge, sur des terrains peu accidentés et à des altitudes plus basses que les groupes de femelles qui se tenaient près des falaises ou des talus à des altitudes plus élevées. Les groupes de femelles sans agneaux s'éloignaient des zones de refuge, mais elles étaient constamment actives (à manger ou à se déplacer). Les indices de densité du brout étaient plus élevés dans les zones utilisées par les mâles que dans les zones fréquentées par les groupes maternels. La composition nutritionnelle était en général semblable dans les deux zones, mais le contenu en fibres était plus grand dans les zones utilisées par les mâles. Les indications de la présence de loups (Canis lupus) et les incidents de prédatio...