Ecological segregation of murres (Uria lomvia, Uria aalge) during the nonbreeding season in the northwest Atlantic ocean

McFarlane Tranquilla, Laura (2014) Ecological segregation of murres (Uria lomvia, Uria aalge) during the nonbreeding season in the northwest Atlantic ocean. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

When resources are limited and similar species co-occur, ecological segregation is likely to occur year-round, through spatial, temporal, behavioural and/or dietary segregation. This study investigates year-round ecological segregation between partially sympatric, congeneric Thick-billed Murres (Uria lomvia) and Common Murres (Uria aalge). In the Northwest Atlantic, the species exhibit a latitudinal divergence in breeding distributions. However, both winter in Low Arctic regions, where the potential for spatial overlap is greater than during the breeding period. Given the inaccessibility of murres at sea, the inter- and intra-specific interactions of murres wintering in the Northwest Atlantic have not been previously studied. Using tracking devices and isotopic analyses, this study integrates spatial and temporal movements during the nonbreeding period, relative overlap of winter habitat, and trophic positions during the nonbreeding period. Thick-billed and Common Murres remained partially segregated throughout the year, with some overlap among particular colony groups. Thick-billed Murres moved over a broad range of latitudes throughout the year, had varied core wintering locations, encountered variable environmental conditions, made variable seasonal movements, and had broad trophic positioning. In comparison, Common Murres concentrated and converged on more narrow wintering areas, where colonies had high spatial overlap, encountered similar environmental conditions with consistent temporal patterns, and occupied similar trophic positions. Habitat segregation occurred mostly spatially; but where spatial overlap was greater, inter-specific dietary segregation increased. Most individual murres (both species) exhibited consistent wintering strategies across 2-3 years, with a few individuals shifting habitats between years. Variation in winter movement patterns stemmed more from between-individual variation (particularly among Thick-billed Murres) than from annual changes within individuals. Ecological segregation is expressed through more varied movement, habitat use, and diets of Thick-billed Murres, resulting in a wider ecological niche that is related both to the range of available habitat and prey, and to inter-specific competitive interactions with Common Murres. Relative connectivity among species and colonies at wintering sites also has implications for overall population vulnerability to spatially-discrete risks or wintering conditions, which will be greater for the relatively concentrated Common Murres than for more dispersed Thick-billed Murres.

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