Trophic Relationships of a Marsh Bird Differ Between Gulf Coast Estuaries |
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Authors: | Scott A Rush Jill A Olin Aaron T Fisk Mark S Woodrey Robert J Cooper |
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Institution: | (1) D.B. Warnell School of Forestry and Natural Resources, University of Georgia, Athens, GA 30602, USA;(2) Great Lakes Institute for Environmental Research, University of Windsor, Windsor, ON, N9B 3P4, Canada;(3) Coastal Research and Extension Center, Mississippi State University, Biloxi, MS 39532, USA;(4) Grand Bay National Estuarine Research Reserve, Moss Point, MS 39562, USA |
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Abstract: | Much of North America’s tidal marsh habitat has been significantly altered by both natural and man-made processes. Thus, there
is a need to understand the trophic ecology of organisms endemic to these ecosystems. We applied carbon (δ
13C) and nitrogen (δ
15N) stable isotope analysis, along with isotope mixing models, to egg yolk, liver, and muscle tissues of clapper rails (Rallus longirostris) and their likely prey items. This analysis enabled us to explore variation in trophic niche and diet composition in this
important marsh bird in two northern Gulf of Mexico tidal marshes that are river and ocean-dominated. For the river-associated
estuary, δ
13C and δ
15N of egg yolks, liver, and pectoral muscle tissue samples provided evidence that clapper rails maintained a similar diet during
both the winter and the breeding season. A trophic link between C3 primary productivity and the clapper rail’s diet was also indicated as the δ
13C of clapper rail egg yolks related negatively with the aerial cover of C3 macrophytes. Clapper rails from the ocean-dominated estuary had a narrower trophic niche and appeared to be utilizing marine
resources, particularly, based on modeling of liver stable isotope values. Variation in stable isotope values between egg
yolk and liver/muscle in both systems suggests that endogenous resources are important for egg production in clapper rails.
These results demonstrate that diet composition, prey source, and niche width of clapper rails can vary significantly across
different estuaries and appear to be influenced by hydrological conditions. |
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