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Accession Number 5004725

Title Use of Stable Isotopes to Determine the Relative Importance of Horseshoe Crab Eggs to

Long-Distance Migrant Shorebirds in Delaware Bay

Project Description Food quality and food availability during stopover are important factors that ultimately define the

migratory and often reproductive fitness of migratory birds. In Delaware Bay, eggs of the Atlantic

horseshoe crab(Limulus polyphemus)have long been believed critical to the maintenance of

long-distant migrant shorebird populations. The age-old spectacle of migrant shorebirds feating on

crab eggs may be threatened by a recent increase in the harvest of horseshoe crabs for

commercial fishing bait. To better understand the importance of horseshoe crab eggs in the diet of

spring-migrant shorebirds,we propose to apply stable isotope methodology to fingerprint foods

used by shorebirds during stopover and determine the relative importance of each in the diet.

Based on procedures developed during a pilot study in FY2000, isotopic signatures of C and N

(and possibly S) will be obtained for plasma and packed cell fractions of small (200ul) blood

samples taken from live-trapped shorebirds. We will demonstrate blood fraction signature changes

for red knots (Calidris canutus) and ruddy turnstones (Arenaria interpres) during May stopover and

relate those changes to the signature values predicted directly from crab eggs and an inventory of

other alternative foods available. In addition, field measurements will be compared to those

obtained in a controlled pen feeding trial that will evaluate isotopic turnover rates and end point

fractionation signature values of captive red knots held on a strict diet of crab eggs. Red knots and

ruddy turnstones that were collected in May 2000 will be used to document isotopic signature of

breast muscle, liver and fat. An effort will be made to inventory the lipid types in shorebird fat

reserves and to fingerprint essential amino acids of other tissues that could possibly be traced

directly to a crab egg diet.

Keywords delaware bay, horseshoe crab, red knot, ruddy turnstone, stable isotope,

Principal Michael Haramis, USGS Patuxent Wildlife Research Center: michael_haramis@usgs.gov; Mark

Investigators A Teece, Dept of Chemistry, SUNY-Syracuse: mteece@esf.edu;

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