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Trophic declines and decadal-scale foraging segregation in three pelagic seabirds

  • Behavioral ecology –original research
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Abstract

We investigated how foraging habits vary among three ecologically distinct wide-ranging seabirds. Using amino acid δ15N proxies for nutrient regime (δ15NPhe) and trophic position (Δδ15NGlu-Phe), we compared Newell’s shearwater (Puffinus newelli) and Laysan albatross (Phoebastria immutabilis) foraging habits over the past 50–100 years, respectively, to published records for the Hawaiian petrel (Pterodroma sandwichensis). Standard ellipses constructed from the isotope proxies show that inter-population and interspecific foraging segregation have persisted for several decades. We found no evidence of a shift in nutrient regime at the base of the food web for the three species. However, our data identify a trophic decline during the past century for Newell’s shearwater and Laysan albatross (probability ≥ 0.97), echoing a similar decline observed in the Hawaiian petrel. During this time, Newell’s shearwaters and Hawaiian petrels have experienced population declines and Laysan albatross has experienced range extension and apparent population stability. Counting other recent studies, a pattern of trophic decline over the past century has now been identified in eight species of pelagic seabirds that breed in the Hawaiian Islands. Because our study species forage broadly across the North Pacific Ocean and differ in morphological and behavioral traits and feeding methods, the identified trophic declines suggest a pervasive shift in food web architecture within the past century.

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Acknowledgements

We thank the Bird Division, National Museum of Natural History, the Bernice Bishop Museum, and the California Academy of Sciences for the loan of specimens and permission to sample them. We are grateful to the National Marine Fisheries Service, Alaska Fisheries Science Center, Pacific Islands Regional Office—Fisheries Observer Program staff and observers, the vessels and crew of the Hawaii longline fisheries that supported the observers, Oikonos and Shannon Fitzgerald, Bill Walker, and Hannah Nevins, in particular, for facilitating sampling of salvaged Laysan albatross. We acknowledge the Hawaii Department of Land and Natural Resources (Division of Forestry and Wildlife) and the Kaua`i Endangered Seabird Recovery Project for facilitating sampling of salvaged Newell’s shearwaters. Funding was generously provided by the National Science Foundation DEB 0,745,604, Michigan State University, and the Wetmore Fund of the Bird Division, Smithsonian Institution.

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Authors and Affiliations

  1. Department of Integrative Biology, Michigan State University, 203 Natural Science Building, 288 Farm Lane, East Lansing, MI, 48824, USA

    Kaycee E. Morra, Hasand Gandhi, Sam Rossman & Peggy H. Ostrom

  2. Institute of Low Temperature Science, Hokkaido University, Kita-19, Nishi-8, Kita-ku, Sapporo, 060-0819, Japan

    Yoshito Chikaraishi

  3. Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, 237-0061, Japan

    Yoshito Chikaraishi

  4. Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, P.O. Box 37012, 10th Street and Constitution Avenue NW, Washington, D.C., 20560, USA

    Helen F. James

  5. Hubbs-SeaWorld Research Institute, 3830 S. Highway A1A #4-181, Melbourne Beach, FL, 32951, USA

    Sam Rossman

  6. Department of Biology, University of Akron, 185 East Mill St, Akron, OH, 44325, USA

    Anne E. Wiley

  7. Kaua`i Endangered Seabird Recovery Project, Hanapepe, Kauai, Hawaii, 96716, USA

    Andre F. Raine

  8. Oikonos Ecosystem Knowledge, P.O. Box 2570, Santa Cruz, CA, 95062, USA

    Jessie Beck

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  1. Kaycee E. Morra
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  2. Yoshito Chikaraishi
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  3. Hasand Gandhi
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  4. Helen F. James
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  5. Sam Rossman
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  6. Anne E. Wiley
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  7. Andre F. Raine
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Contributions

KEM, PHO, HFJ, and AEW formulated the idea. KEM, PHO, and SR wrote the manuscript. All authors engaged in intellectual exchange and manuscript editing. KEM, PHO, YC, and HG developed methodology and performed laboratory analyses. SR and KEM performed statistical analyses. AR and JB facilitated access to salvaged birds. KEM, AEW, HFJ, AR, and PHO collected samples.

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Correspondence to Kaycee E. Morra.

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Additional information

Communicated by Seth Newsome.

This study is the first to develop decadal-scale amino acid nitrogen isotope chronologies on bone collagen of threatened and endangered seabirds. We identify a pattern of long-term stability in trophic segregation coupled with recent trophic decline in three species of Hawaiian seabirds.

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Morra, K.E., Chikaraishi, Y., Gandhi, H. et al. Trophic declines and decadal-scale foraging segregation in three pelagic seabirds. Oecologia 189, 395–406 (2019). https://doi.org/10.1007/s00442-018-04330-8

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