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Combined measurements of egg fatty acids and stable isotopes as indicators of feeding ecology in lake‐dwelling birds
Author(s) -
RAMÍREZ FRANCISCO,
JOVER LLUÍS,
SANPERA CAROLINA,
RUIZ XAVIER,
PIQUÉ ESTER,
GUITART RAIMON
Publication year - 2009
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/j.1365-2427.2009.02226.x
Subject(s) - trophic level , biology , ecology , macrophyte , predation , invertebrate , cormorant , food chain , polyunsaturated fatty acid , δ15n , isotope analysis , zoology , fatty acid , stable isotope ratio , δ13c , biochemistry , physics , quantum mechanics
Summary 1. We examined whether egg fatty acid (FA) profiles and stable isotopes (SIA) could be used in a comparative way to infer the diet of two aquatic bird species with contrasting feeding habits: a surface forager, the pheasant‐tailed jacana ( Hydrophasianus chirurgus ), and a pursuit‐diving forager, the little cormorant ( Phalacrocorax niger ), at Haleji Lake (Pakistan). 2. The species differed markedly in the overall percentage of saturated and polyunsaturated fatty acids. Moreover, among jacanas, two groups of birds had relatively high or low concentrations of long‐chain essential PUFAs (such as 18:2 n‐6 and 20:4 n‐6), suggesting differing contributions from animal prey and plant material. 3. These trophic differences were corroborated by δ 15 N values which indicated both a higher trophic position in cormorants relative to jacanas, and differences in trophic position for the two groups of jacanas. In this latter species δ 13 C values in both groups also pointed to differing diets, involving mainly grazing plants or a contribution from animal resources (aquatic invertebrates or insects). 4. Both lower values of δ 13 C and higher percentages of 18:1 n‐7 detected in little cormorants may indicate the influence of the anoxic water, typical of a freshwater system densely covered by macrophytes. 5. These results indicate how both biomarkers offer complementary information in studies of feeding ecology, refining interpretations of trophic pathways which are usually based on FA or SIA alone. Comparisons of FA profiles and SIA among species also proved to be a reliable approach for inferring the diet of species for which information is scarce or contradictory, as is the case for the pheasant‐tailed jacana.