447 ARTICLE Ecological segregation among Thick-billed Murres (Uria lomvia) and Common Murres (Uria aalge) in the Northwest Atlantic persists through the nonbreeding season L. McFarlane Tranquilla, W.A. Montevecchi, A. Hedd, P.M. Regular, G.J. Robertson, D.A. Fifield, and R. Devillers Abstract: To study the influence of inter- and intra-specific interactions on patterns of ecological segregation in nonbreeding habitat, we used geolocators to track year-round movements of congeneric and partially sympatric Thick-billed Murres (Uria lomvia (L., 1758)) and Common Murres (Uria aalge (Pontoppidan, 1763)) from seven Canadian colonies during 2007–2011. Locations from 142 individuals were (i) examined for species- and colony-specific spatiotemporal patterns, (ii) mapped with environmental data, and (iii) used to delineate core wintering areas. Compared with Common Murres, Thick-billed Murres dispersed across a wider range of latitudes and environments, had larger winter ranges, and showed greater variation in seasonal timing of movements. These interspecific differences were consistent at two scales: among colonies spanning a wide latitudinal range and at a sympatric colony. Intraspecifically, nonbreeding ecological segregation was more pronounced among colonies of Thick- billed Murres than of Common Murres: colonies of Thick-billed Murres tended to follow distinct movement patterns and segregate by latitude, whereas colonies of Common Murres segregated very little; moreover, the extent of segregation was more variable among Thick-billed Murres than Common Murres. For Thick-billed Murres, rather than complete divergence of winter ecological niche from Common Murres, we found a “widening” of an overlapping niche. This strategy of increased movement flexibility may enable Thick-billed Murres to mitigate competition both intra- and inter-specifically; we propose this movement strategy may have played a role in species divergence. Key words: Uria aalge, Uria lomvia, movement ecology, niche segregation, seabird tracking, wintering areas, seasonal variation. Résumé : Afin d’étudier l’influence des interactions interspécifiques et intraspécifiques sur les motifs de ségrégation écologique dans les habitats autres que de reproduction, nous avons utilisé des géolocalisateurs pour suivre les déplacements durant toute l’année de guillemots de Brünnich (Uria lomvia (L., 1758)) et de guillemots marmettes (Uria aalge (Pontoppidan, 1763)) congénères et partiellement sympatriques de sept colonies canadiennes, de 2007 a` 2011. Les emplacements de 142 individus ont été For personal use only. (i) examinés pour en déterminer les motifs spatiotemporels propres a` chaque espèce et a` chaque colonie, (ii) cartographiés avec des données expérimentales et (iii) utilisés pour délimiter les aires d’hivernage principales. Par rapport aux guillemots marmettes, les guillemots de Brünnich se dispersaient sur une plus grande fourchette de latitudes et de milieux et présentaient des aires d’hivernage plus grandes et une plus grande variation du moment des déplacements durant les saisons. Ces différences interspécifiques étaient cohérentes a` deux échelles, soit entre différentes colonies couvrant une large fourchette de latitudes et a` l’intérieur d’une colonie sympatrique. Au sein de l’espèce, la ségrégation écologique en dehors de la période de reproduction était plus prononcée entre les colonies de guillemots de Brünnich qu’entre celles de guillemots marmettes; les colonies de guillemots de Brünnich tendaient a` suivre des motifs de déplacements distincts et a` se ségréger selon la latitude, alors que les colonies de guillemots marmettes ne présentaient qu’une très faible ségrégation; en outre, l’ampleur de la ségrégation était plus variable chez les guillemots de Brünnich que chez les guillemots marmettes. Plutôt qu’une divergence complète de la niche écologique hivernale des guillemots de Brünnich par rapport a` celle des guillemots marmettes, nous avons observé « l’élargissement » d’une niche chevauchante commune. Cette stratégie de souplesse accrue des déplacements pourrait per- mettre aux guillemots de Brünnich d’atténuer la concurrence tant intraspécifique qu’interspécifique; nous proposons que cette stratégie de déplacement pourrait avoir joué un rôle dans la divergence des espèces. [Traduit par la Rédaction] Mots-clés : Uria aalge, Uria lomvia, écologie des déplacements, ségrégation de niche, localisation d’oiseaux marins, aires d’hivernage, variations saisonnières. Introduction dietary partitioning, exhibiting varied patterns of space use, for- When resources are limited, sympatric and competing species aging activity, and diet (MacArthur and Levins 1964; Phillips et al. Can. J. Zool. Downloaded from www.nrcresearchpress.com by MEMORIAL UNIV OF NEWFOUNDLAND on 05/31/18 are able to coexist through ecological segregation (Lack 1945; Holt 2009; Masello et al. 2010), all of which are well-documented strat- 2009). Sympatric species reduce competition through habitat and egies of niche partitioning at colony sites during the breeding Received 30 November 2014. Accepted 25 March 2015. L. McFarlane Tranquilla,* W.A. Montevecchi, A. Hedd, and P.M. Regular. Cognitive and Behavioural Ecology, Department of Psychology, Memorial University of Newfoundland, St. John’s, NL A1B 3X9, Canada. G.J. Robertson and D.A. Fifield. Wildlife Research Division, Environment Canada, 6 Bruce Street, Mount Pearl, NL A1N 4T3, Canada. R. Devillers. Department of Geography, Memorial University of Newfoundland, St. John’s, NL A1B 3X9, Canada. Corresponding author: L. McFarlane Tranquilla (e-mail: [email protected]). *Present address: Bird Studies Canada, 17 Waterfowl Lane, Sackville, NB E4L 1G6, Canada. Can. J. Zool. 93: 447–460 (2015) dx.doi.org/10.1139/cjz-2014-0315 Published at www.nrcresearchpress.com/cjz on 13 April 2015. 448 Can. J. Zool. Vol. 93, 2015 season (Wood et al. 2000; Grémillet et al. 2004; Gonzáles-Solís and Hipfner 2000; Ainley et al. 2002). Because the two species are et al. 2007; Wakefield et al. 2013). Following breeding, seabirds are morphologically and ecologically very similar (Gaston and Jones released from central-place foraging constraints and, given the 1998), competition and pressures for divergence between them is potential for dispersal throughout the marine environment, one likely intense. Dietary niche partitioning is supported by slight might expect a reduction in resource competition that diffuses differences in bill morphology (Bédard 1969) reflecting preferences: the pressure for ecological segregation. However, marine re- Thick-billed Murres consume a wide variety of fishes (e.g., sources are patchily distributed, and important wintering areas Arctic cod (Boreogadus saida (Lepechin, 1774)), blennies (suborder can concentrate large numbers of nonbreeding seabirds and other Blennioidei)) and zooplankton (for which their tongue and palate top predators (e.g., Grand Banks of Newfoundland: Frederiksen are better adapted; Bédard 1969), whereas Common Murres con- et al. 2011; Hedd et al. 2012; Mosbech et al. 2012; Magnusdottir et al. sume predominantly shoaling fishes (e.g., capelin (Mallotus villosus 2012; Mid-Atlantic Ridge: Walli et al. 2009; Egevang et al. 2010; (Müller, 1776)), sand lance (genus Ammodytes L., 1758)) with a small North Pacific Transition Zone: Block et al. 2011; Benguela Upwell- proportion of invertebrates (Gaston and Jones 1998). In the North- ing: Stenhouse et al. 2011), where competition for resources is west Atlantic, they have a relatively segregated breeding distribu- likely to persist. Here, how inter- and intra-specific interactions tion (Thick-billed Murres concentrating at higher latitudes; see may influence ecological segregation in wintering areas (Ratcliffe also study colony sizes in Table 1), but sympatry occurs where et al. 2014) is another important piece of the puzzle. their ranges overlap. At sympatric colonies, subtle differences Research on ecological segregation among nonbreeding sea- in phenology, breeding-site locations, and prey exploitation birds has unfolded using two approaches. First, studies dedicated might decrease interspecific competition (Birkhead and Nettleship to investigating nonbreeding segregation usually compare winter 1987a, 1987b; Barrett et al. 1997). Following breeding, both species distributions of sympatric species or neighboring populations. winter at Low Arctic latitudes of the North Atlantic Ocean (Tuck Among the most well-studied have been seabirds of the Southern 1961; Gaston and Hipfner 2000; Ainley et al. 2002). Although Tuck Atlantic and Indian oceans, where sympatric groups (e.g., petrels, (1961) considered them to segregate partially by thermal prefer- albatrosses, penguins) from Antarctic colonies exhibit species- ence (with Thick-billed Murres occurring in colder waters and specific segregation into different water masses of the Antarctic Common Murres occurring in warmer waters), other studies have Circumpolar Current, usually targeting different diets (Cherel blurred this categorization, rendering it unclear how winter strat- et al. 2006, 2007; Phillips et al. 2009; Thiebot et al. 2012; Ratcliffe egies or preferences of murres are influenced by geography and et al. 2014). Winter spatial and diet segregations by sex also occurs habitat preference, colony of origin, or the presence of competi- in some species (Phillips et al. 2005). Very few studies have com- tors (Gaston et al. 2011, Fort et al. 2012, Linnebjerg et al. 2013). In pared nonbreeding segregation outside the Antarctic system. the