4.4 Article

Moult chronology and strategies of sympatric Great (Ardenna gravis) and Sooty (A. grisea) Shearwaters based on stable isotope analysis

Journal

IBIS
Volume 164, Issue 4, Pages 998-1012

Publisher

WILEY
DOI: 10.1111/ibi.13060

Keywords

Ardenna; feathers; moulting; primaries; shearwaters; stable isotope; Staffelmauser

Categories

Funding

  1. Natural Sciences and Engineering Research Council of Canada (NSERC) [2014-06290]
  2. University of Manitoba Faculty of Science
  3. NSERC Ship Time grants [453216-2014, 470195-2015]
  4. Science without Borders
  5. Coordination for the Improvement of Higher Education Personnel CAPES, Brazil [001203/2013-04]
  6. Conselho Nacional de Desenvolvimento cientifico e Tecnologico - CNPq, Brazil [PQ 311409/2018-0]
  7. Grand Manan Whale and Seabird Research Station (GMWSRS)
  8. New Brunswick Wildlife Trust Fund

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This study used stable isotope ratios to investigate the moulting location and diet of Great and Sooty Shearwaters. The results showed that both species completed their moult in coastal Newfoundland, with some differences in moult advancement. The study also revealed divergent locations and diets during early moult, but convergence in diet when the feathers of both species were sampled in coastal North America. Protecting this moulting area is essential to minimize disturbance and threats to these species.
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 (delta N-15, delta C-13) 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 (delta N-15 = 15.17 +/- 1.13 parts per thousand; delta C-13 = -18.66 +/- 0.54 parts per thousand) and Sooty Shearwaters (15.54 +/- 0.74 parts per thousand; -18.43 +/- 0.78 parts per thousand); 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 delta N-15 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.

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