Shorebirds, Stakeholders, and Competing Claims to the Beach and Intertidal Habitat in Delaware Bay, New Jersey, USA

Lawrence Niles,Joanna Burger

doi:10.4236/ns.2017.96019

Abstract

Birds have specific habitat needs as a function of their life cycle and reproductive stage. Migrant shorebirds that may fly from the Arctic to the southern tip of South America have foraging and habitat requirements at sites where they stop to refuel before continuing their migration north or south. Throughout the world, shorebirds mainly forage on mudflats at low tide. Red knots (Calidris canutus rufa) are threatened in the United States and elsewhere, and it is critical to determine factors that might contribute to their decline. This paper uses Delaware Bay as a case study to examine shorebird (and red knot) use of the intertidal habitat, and competing claims to habitats they require during their northward migration, as well as some of the key stakeholders that play a role in protecting red knots. Shorebirds are drawn to Delaware Bay to feed on the eggs of Horseshoe Crabs (Limulus polyphemus) that are concentrated at the high tide. But they also feed on the intertidal mudflat. We examined intertidal habitat use on 17 beaches in an extensive study in 2015, and 5 key beaches in 2016. Most of the beaches were longitudinal, but four were more complex, and were used extensively for resting as well as foraging; numbers there were higher than on the longitudinal beaches. On foraging beaches, some shorebirds were present on over 85% of the intertidal censuses, and red knots were present on over 48% of the intertidal censuses. Average numbers of red knots on the longitudinal beaches varied from 0 to 354 ± 116 when any shorebirds were present, but averaged up to 1184 ± 634 when knots were present in 2015. Some beaches in 2015 had no knots (a beach with long-term aquaculture). Tide, intertidal location, and beach (name) determined the number of knots (and all shorebirds). Numbers decreased with distance from the mean high tide line. The average number of knots present in the intertidal mudflats two hours before or after low tide when knots were present (e.g. no censuses with zeros) was 2040 (=maximum flock size, in 2015). Major threats to red knots are from recreationists, overfishing of horseshoe crabs (reduction in egg prey base), and use of the intertidal by aquaculture. We discuss the role of stakeholders in conservation and protection of red knots.

Highlights

Animals have specific habitat requirements that contribute to their survival, reproduction, and longevity
We examine some of the factors affecting survival and population levels of red knots (Calidris canutus rufa) stopping over on Delaware Bay, New Jersey, including competing uses of beaches by recreationists, fisherman, and aquaculture
Over the last 20 years most of the studies on foraging have focused on high tide when shorebirds forage on horseshoe crab eggs, they forage on intertidal mudflats, the subject of our results presented below, and roost on the high beach or sand bars when not foraging

Summary

Introduction

Animals have specific habitat requirements that contribute to their survival, reproduction, and longevity. The risk animals’ face throughout the year often depends upon one or more bottleneck locations where resources (habitat, food) are limited, or where human activities provide a disturbance. This is especially true for long-distance migrants, such as shorebirds that migrate from Arctic or sub-Arctic breeding grounds to the southern hemisphere. Red Knots may live 12 - 15 years, but they do not breed until they are 2 - 3 years old [18] On their way north each spring, a significant portion of the Northern Hemisphere’s rufa population migrates through Delaware Bay [18, 19].

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