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Stable Isotope Analysis of Marbled Murrelets: Evidence for Freshwater Feeding and Determination of Trophic Level

Keith A. Hobson
The Condor
Vol. 92, No. 4 (Nov., 1990), pp. 897-903
DOI: 10.2307/1368725
Stable URL: http://www.jstor.org/stable/1368725
Page Count: 7
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Stable Isotope Analysis of Marbled Murrelets: Evidence for Freshwater Feeding and Determination of Trophic Level
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Abstract

Stable carbon and nitrogen isotopic analyses were performed on tissues of 21 Marbled Murrelets (Brachyramphus marmoratus) collected in Barkley Sound (n = 18) and on Johnston Lake, British Columbia (n = 3). Three adult males had significantly lower muscle tissue δ 13C values (x̄ ± SD: -23 ± 2.7‰, n = 3) than did all other murrelets (- 16.5 ± 0.6‰, n = 18). Based on a model predicting muscle δ 13C values for murrelets feeding on freshwater and marine prey these three individuals had short-term freshwater-derived protein inputs to their diets ranging from 50 to 100%. The mean δ 13C value for Marbled Murrelet bone collagen (- 16.8 ± 0.3‰, n = 4) was not significantly different from that found for Ancient Murrelets (Synthliboramphus antiquus) from Reef Island, Queen Charlotte Islands. This suggests that while some Marbled Murrelets may feed exclusively on freshwater prey for a short but important period of several weeks, freshwater protein is not a significant long-term dietary component in their diets. Marbled Murrelets had a mean muscle δ 15N value of 15.3 ± 0.7‰ (n = 21). Because δ 15N values for freshwater and marine prey species overlapped significantly, stable-nitrogen isotope analysis did not distinguish between Marbled Murrelets feeding on freshwater or marine prey. The stable-nitrogen isotope values of muscle tissue from Marbled Murrelets were compared with those of nine other species of alcids from British Columbia and the high Arctic. The comparison indicates that stable-nitrogen isotope analysis is potentially useful for establishing trophic relationships in seabird communities.

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