Shorebird Predation on Eggs of Horseshoe Crabs during Spring Stopover on Delaware Bay

The Horseshoe Crab, Limulus polyphemus: 200 Million Years of Existence, 100 Years of Study

“…Castro et al (1989) report that during the 2 to 3 week time period the birds stay on Delaware Bay, they undergo weight gains of at least 40% of their body weight. It has been estimated that all shorebirds consume 5526.2 × 10 6 kJ of energy for their trip, equivalent to approximately 539 metric tons of horseshoe crab eggs (Castro and Myers, 1993). One reason this number is so large is because of the low metabolic efficiencies of the birds, which Castro et al (1989) attribute to the low number of eggs that are actually broken down when passing through the birds' gastrointestinal tracts, as the egg's cuticle resists chemical and enzymatic digestion.…”

“…Thus, it has been estimated that 1,820,000 female horseshoe crabs are required to feed Delaware Bay's migratory birds (Castro and Myers, 1993). These calculations assume that shorebirds are feeding exclusively on horseshoe crab eggs (Castro and Myers, 1993), but they may augment their diet with other food sources (Botton, 1984a), including invertebrates (Clark, 1996). In addition to birds feeding on the eggs of horseshoe crabs, there is also evidence of birds feeding on adult horseshoe crabs Loveland, 1989, 1993).…”

“…The value of assimilation efficiency is assumed to be similar for all species, because assimilation efficiency seems to be primarily a function of food consumed (Castro et al, 1989;Castro and Myers, 1993). Thus, it has been estimated that 1,820,000 female horseshoe crabs are required to feed Delaware Bay's migratory birds (Castro and Myers, 1993).…”

“…These species include red knots (Calidris canutus), ruddy turnstones (Arenaria interpres), sanderlings (C. alba), and semipalmated sandpipers (C. pusilla) (Shuster, 1982a), as well as dunlins (C. alpina) and dowitchers (Limnodromus spp.) (Dunne et al, 1982;Castro and Myers, 1993), and laughing gulls (Larus atricilla) (Botton, 1984b), all of which use the Delaware Bay region as a staging area during their migration. According to Botton et al (1994), staging areas serve as intermediate stopover points for the birds to feed before continuing their migration.…”

“…The value of assimilation efficiency is assumed to be similar for all species, because assimilation efficiency seems to be primarily a function of food consumed (Castro et al, 1989;Castro and Myers, 1993). Thus, it has been estimated that 1,820,000 female horseshoe crabs are required to feed Delaware Bay's migratory birds (Castro and Myers, 1993). These calculations assume that shorebirds are feeding exclusively on horseshoe crab eggs (Castro and Myers, 1993), but they may augment their diet with other food sources (Botton, 1984a), including invertebrates (Clark, 1996).…”