ABSTRACT: Stable-isotope ratios of carbon (d13C) were determined in liver samples from a number of procellariiform seabirds from New Zealand. Generally, d13C values were low (depleted in ¹³C) and there was a significant degree of intra- and inter-specific variation. We suggest that the pelagic versus inshore/benthic foraging model for d13C values in marine consumers is insufficient to explain the intra- and inter-specific variation. Nor can observed d13C values of procellariforms be linked to variation in foraging distances. We propose that carbon relatively depleted in ¹³C derived from dietary lipids is incorporated into proteins. Support for this hypothesis is provided by depleted d13C signatures we measured in lipids extracted from liver tissue, which were always lower than d13C signatures in liver tissue (by 4.2 to 6.8[per thou], depending on species). Additionally, d13C values were determined in a small number of stomach-oil samples; these too were relatively depleted and lower than d13C values measured in liver tissue. Incorporation of dietary lipids, relatively depleted in ¹³C, into protein could explain both intra- and inter-specific variation in d13C signatures in procellariiforms and may represent an additional explanation for relatively low d13C values in pelagic consumers.

KEY WORDS: Stable isotopes · Diet · New Zealand · Seabird · Foraging

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Published in MEPS Vol. 208 (2000) on December 8
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 2000