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Stable isotope and pen feeding trial studies confirm the value of horseshoe crab Limulus polyphemus eggs to spring migrant shorebirds in Delaware Bay

Journal of Avian Biology

doi:10.1111/j.2006.0908-8857.03898.x 6767_Haramis.pdf
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Abstract

We used stable isotope (SI) methods in combination with pen feeding trials to determine the importance of eggs of the Atlantic horseshoe crab Limulus polyphemus to migratory fattening of red knots Calidris canutus rufa and ruddy turnstones Arenaria interpres morinella during spring stopover in Delaware Bay. By manifesting measurable fractionation (ca +3?) and rapid turnover, blood plasma *15 nitrogen proved a functional marker for SI diet tracking during the short 3-week stopover. Blood samples from free-ranging knots (3 data sets) and turnstones (1 data set) produced similar convergence of plasma *15 N signatures with increasing body mass that indicated highly similar diets. Asymptotes deviated slightly (0.3? to 0.7?) from that of captive shorebirds fed a diet of only crab eggs during stopover, thus confirming a strong crab egg-shorebird linkage. The plasma *15N crab-egg diet asymptote was enriched ca +4.5? and therefore readily discriminated from that of either blue mussels Mytilus edulis or coquina clams Donax variabilis, the most likely alternative prey of knots in Delaware Bay. Crab eggs were highly palatable to captive knots and turnstones which achieved rates of mass gain (3?11 g/d) comparable to that of free-ranging birds. Peak consumption rates during hyperphagic events were 23,940 and 19,360 eggs/bird/d, respectively. The empirical conversions of eggs consumed to body mass gained (5,017 eggs/g for knots and 4,320 eggs/g for turnstones) indicate the large quantities of crab eggs required for the maintenance of these shorebird populations during stopover.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Stable isotope and pen feeding trial studies confirm the value of horseshoe crab Limulus polyphemus eggs to spring migrant shorebirds in Delaware Bay
Series title:
Journal of Avian Biology
Volume
38
Issue:
3
Year Published:
2007
Language:
English
Contributing office(s):
Patuxent Wildlife Research Center
Description:
367-376
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Journal of Avian Biology
First page:
367
Last page:
376