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Moult is an energetically demanding period, during which flight may be impaired and foraging ranges may become constrained. During the non‐breeding period, Great Ardenna gravis and Sooty Ardenna grisea Shearwaters migrate from South Atlantic breeding colonies to aggregate at North Atlantic feeding grounds. We investigated whether both shearwater species used coastal Newfoundland, Canada, as a moulting area and used stable isotope ratios (δ15N, δ13C) of recently moulted primary feathers (P1, P5, P10) to infer moult location/diet for both species. Moult scores indicated that both species finished their moult (i.e. P6–10) in coastal Newfoundland, which was further corroborated with similar stable isotope ratios for Great (δ15N = 15.17 ± 1.13‰; δ13C = −18.66 ± 0.54‰) and Sooty Shearwaters (15.54 ± 0.74‰; −18.43 ± 0.78‰); however, Sooty Shearwater moult was more advanced relative to that of Great Shearwater. In contrast, isotopic ratios of P1 and P5, which were grown before arriving in coastal Newfoundland, differed between and within species, suggesting divergent locations/diet during early moult. For Great Shearwaters, P1/P5 isotopic ratios were more variable (broader niche breadth) than P10, suggesting that some individuals started moulting in the South Atlantic prior to trans‐equatorial migration, whereas others start moulting in the North Atlantic Ocean. Sooty Shearwaters had two distinct groupings of either higher or lower δ15N in P1/P5, suggesting that individuals began moulting either on the Newfoundland Shelf or further offshore based on comparisons to reference shearwater feathers grown in known locations. These findings illustrate distinct locations and/or diets at the start of primary feather moult, both within and between species, but diets converged when aggregated together at the end of moult in coastal North America, where growing feathers of both species were sampled. More importantly, we identified an important area for both Sooty and Great Shearwaters to complete their moult in coastal Newfoundland. Protecting this moulting area would minimize disturbance and the impacts of threats (e.g. by‐catch) to both species during this energetically demanding period. The area has been suggested previously to be an important candidate area for protection due to annually persistent prey aggregations that can be spatiotemporally delimited based on specific prey habitat requirements. [ABSTRACT FROM AUTHOR]

Little is known about the movements of small seabirds during migration, but such information is important for their conservation. Leach's Storm Petrel Oceanodroma leucorhoa is the most abundant seabird in Atlantic Canada, but its population has declined in recent years. Here, we describe trans-equatorial and trans-Atlantic migration movements of 13 Leach's Storm Petrels, which were tracked with geolocators from two breeding colonies in Nova Scotia, Canada: Bon Portage Island and Country Island. Our results indicate that Leach's Storm Petrels have low migratory connectivity and that they use multiple stopover areas and overwintering destinations. Birds with stopover areas at higher latitudes overwintered in the North Atlantic Ocean, either in areas associated with the North Equatorial Current or in waters off Newfoundland and Labrador. Birds with lower-latitude stopover areas overwintered in the South Atlantic Ocean, in areas associated with the Benguela Current off southwestern Africa. We observed greater δ15N values (indicating a higher trophic level) in feathers from birds that migrated south compared to birds that stayed in the Northern Hemisphere, but we observed no difference in δ13C (which may be interpreted in multiple ways). Species distribution modelling using remotely sensed oceanographic data indicated that high sea surface temperatures and high chlorophyll a concentrations were important predictors of habitat use in winter. [ABSTRACT FROM AUTHOR]

The Leach's storm-petrel (Hydrobates leucorhous) is one of the most abundant and widely distributed marine birds in the North Atlantic but is under global population decline, possibly linked to marine pollution. We determined levels of ingested plastic and hepatic total mercury (THg) in recently fledged juveniles that stranded in Newfoundland and Labrador, Canada, and assessed the relationship to body condition, size and diet. Plastic prevalence was high (87.5%) but hepatic THg was relatively low (mean 486.7 ng/g dry weight) compared to other studies. Levels of neither pollutant were significantly related to body metrics of health. Our data confirm that plastic and mercury are pervasive in the western North Atlantic Ocean, prominent even in young birds. • A mass stranding event allowed recently fledged Leach's storm-petrels to be sampled. • 87.5% of recently fledged birds contained plastic pollution. • Average hepatic THg (mean 486.7 ng/g) was lower than adults. • Plastic pollution and mercury pollution were not significantly correlated with bird body condition. [ABSTRACT FROM AUTHOR]

Interspecific interactions help to shape individual- and population-level dynamics. As such, similar species breeding sympatrically are expected to have a high potential for competition and, thus, may have developed strategies to reduce niche overlap to allow coexistence. We combined GPS tracking and stable isotope analysis (δ15N, δ13C) to simultaneously compare multiple behavioral and dietary niche dimensions of common murres (Uria aalge) and razorbills (Alca torda) breeding at nearby colonies (55 km apart) on the northeastern Newfoundland coast under varying prey availability in 2017. Though foraging ranges of species had high potential overlap (5000 km2), foraging areas of the two species were spatially segregated. Dive characteristics also differed, as predicted based on body size and dive capacity. These differences contrasted a high degree of overlap in diet, habitat characteristics, and diurnal foraging patterns, suggesting that spatial segregation may be the most important factor to allow coexistence of these similar species for the same limited resources. As prey availability increased later in the breeding season, individual murres and razorbills foraged closer to their respective colonies and population-level diet composition changed, indicative of reduced energy costs and dietary plasticity to take advantage of highly available prey, capelin (Mallotus villosus). Foraging areas, however, remained segregated. Seabirds and marine systems face many potential threats, the greatest of which may be climate change. Thus, understanding variation in space, time, and habitat selection among similar species allowed for a more comprehensive view of the possible ways these species may partition their niche and how future changes to resource availability could impact interspecific relationships. [ABSTRACT FROM AUTHOR]