Molecular Analysis of the Value of Horseshoe Crab Eggs to Migrating Shorebirds

Abstract

Detection of prey DNA from faecal samples is a non-invasive method being successfully applied to the dietary analysis of birds as well as other vertebrates and invertebrates. We have employed this technique to examine the significance of Horseshoe Crab eggs (Limulus polyphemus) for Dunlins (Calidris alpina), Semipalmated Sandpipers (Calidris pusilla), Least Sandpipers (Calidris minutilla) and Short-billed Dowitchers (Limnodromus griseus) during northbound migration at their major stopover area in Delaware Bay. This was accomplished through polymerase chain reaction amplification of Limulus DNA from faecal samples using new Horseshoe Crab-specific primers. We detected the consumption of crab eggs in all study species, although results suggest that eggs may be a less important food source for Least Sandpipers than for the other species. Consumption of eggs increases as the migration season progresses, implying a strong preference of birds for this resource at the end of May, when eggs are readily accessible. The results confirm the value of Horseshoe Crab eggs for migrating shorebirds in this crucial stopover area. The Limulus-specific primers we designed can be effectively used for detection of semidigested Limulus DNA from faecal samples and thus they can be employed in the dietary analysis of other predators that seasonally capitalise on Horseshoe Crabs or their eggs.

Phenological mismatch in Arctic‐breeding shorebirds: Impact of snowmelt and unpredictable weather conditions on food availability and chick growth

“…In addition, dietary analyses based on gut contents can have several drawbacks, including unequal digestion and retention of prey (Tollit, Wong, Winship, Rosen, & Trites, 2003), errors in identification of prey (Clare, Fraser, Braid, Fenton, & Herbert, 2009), and over-simplification of prey composition due to difficult visual identification of closely related taxa. While new genetic techniques may improve our understanding of the prey items consumed (Gerik, 2018;Gerwing, Kim, Hamilton, Barbeau, & Addison, 2016;Novcic, Mizrahi, Veit, & Symondson, 2015;Symondson, 2002;Wirta et al, 2015), care must be used in implementing and interpreting these techniques as well (Oehm, Juen, Nagiller, Neuhauser, & Traugott, 2011;Valentini, Pompanon, & Taberlet, 2009). As different insect taxa have different emergence patterns (Butler, 1980, Høye & Forchhammer, 2008, Braegelman, 2016; and see Figure S1), dietary information is crucial to developing accurate prey availability curves (Vatka, Orell, & Rytkönen, 2016).…”

Heavy Metals in Biota in Delaware Bay, NJ: Developing a Food Web Approach to Contaminants

“…Finally, this paper represents the first stage of a trophic level analysis of biota in Delaware Bay. The Bayhas lost much of its commercial and recreational fishing because of collapses in fish populations, and it supports far fewer populations of migrating shorebirds, experiences industrial and agricultural pollution, and is facing additional habitat losses because of sea level rise [24,25,26,27,28,36,38,55]. To some degree, this paper is a call to gather more information on contaminant levels in more nodes on the food web so that the keystone species can be identified, the possible causal role of contaminants in species declines can be examined, and possible remedies can be identified and implemented.…”

“…In this paper we describe a food web for Delaware Bay, and examine cadmium (Cd), lead (Pb), mercury (Hg), and selenium (Se) levels in some of the biota for a springtime (May to early June) food web when shorebirds gather there in large numbers during their northward migration. We focused on shorebirds because they are transient and eat mainly crab eggs while staying at the Bay [24,25,26,27,28]. At other times and places their diet is more varied, making it more difficult to examine contaminants in their prey [29,30].…”

Effect of forager density on feeding rates in spring-staging Semipalmated Sandpipers (Calidrispusilla) using different foraging modes

“…Annelids were the D r a f t most abundant benthic invertebrates, and besides the two most abundant families, spionids and nereids, this prey category also included capitellids and tubificids. The "all prey taxa" category included nemerteans, bivalves, amphipods, isopods, insect larvae, and unidentified individuals (Novcic et al 2015…”

“…Here, we investigated the influence of the density of foragers on feeding rates in semipalmated sandpipers (Calidris pusilla (L., 1766)) that use different foraging techniques at a spring stopover site in Delaware Bay, USA. Each spring, this area attracts large number of shorebirds that capitalize on eggs of spawning horseshoe crabs (Limulus polyphemus (L., 1758)) (Myers 1986;Novcic et al 2015). Although large mixed-species flocks forage along sandy beaches where horseshoe crabs spawn (Myers 1986;Botton et al 1994;Tsipoura and Burger 1999), a considerable number of birds also use intertidal marshes and mudflats where they feed on various invertebrates (Burger et al 1997;Tsipoura and Burger 1999;Novcic et al 2016).…”