Site selection by migratory shorebirds in Delaware Bay, and its relationship to beach characteristics and abundance of horseshoe crab (Limulus polyphemus) eggs
TL;DR: The distribution of migratory shorebirds within Delaware Bay, New Jersey, was examined relative to prey abundance and the physical characteristics of the intertidal beaches as mentioned in this paper, and the most abundant food item on these beaches was horseshoe crab (Limulus polyphemus) eggs, and there were few other available macroinvertebrates.
Abstract: -The distribution of migratory shorebirds within Delaware Bay, New Jersey, was examined relative to prey abundance and the physical characteristics of the intertidal beaches. Red Knots (Calidris canutus), Sanderlings (C. alba), Ruddy Turnstones (Arenaria interpres), and "peeps" comprised nearly 100% of the shorebirds on seven study beaches from mid-May to early June in both 1990 and 1991. The most abundant food item on these beaches was horseshoe crab (Limulus polyphemus) eggs, and there were few other available macroinvertebrates. Beaches preferred by shorebirds had higher numbers of crab eggs; the density of eggs in some surface (0-5 cm) sediments exceeded 1 05 / M2. In general, both horseshoe crab eggs and shorebirds increased along the bay shore from Higbee's Beach (near Cape May Point) to Moore's Beach, 32 km up-bay. However, shorebirds were widely distributed within the bay, possibly because eggs were sufficiently abundant on most beaches to support foraging by at least four birds per meter of shoreline. Shorebirds aggregated near shoreline discontinuities, such as salt-marsh creeks and jetties, that acted as concentrating mechanisms for passively drifting eggs. Sediment grain size and heterogeneity were probably not a primary determinant of shorebird distribution within Delaware Bay. Intertidal sand flats were not extensively used by foraging shorebirds, but the potential importance of nearby salt marshes as foraging sites requires further investigation. Received 20 January 1993, accepted 27 March
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TL;DR: A review of the literature on ocean sandy beaches can be found in this paper, where the authors provide an introduction to much of the relevant literature, and predicting possible states of the system by 2025.
Abstract: Pollution, mining, disruption of sand transport and tourism development widely affect sandy shores, and these systems may be subject to increased erosion in future, yet there have been few attempts to review them. The present review focuses largely on ocean sandy beaches, providing an introduction to much of the relevant literature, and predicting possible states of the system by 2025. Sandy shores are dynamic harsh environments, the action of waves and tides largely determining species diversity, biomass and community structure. There is an interchange of sand, biological matter and other materials between dunes, intertidal beaches and surf zones. Storms and associated erosion present the most substantial universal hazard to the fauna. Human-related perturbations vary from beach to beach; however, structures or activities that impede natural sand transport or alter the sand budget commonly lead to severe erosion, often of a permanent nature. Many beaches also suffer intermittent or chronic pollution, and direct human interference includes off-road vehicles, mining, trampling, bait collecting, beach cleaning and ecotourism. These interferences typically have a negative impact on the system. Identified long-term trends include chronic beach erosion, often largely due to natural causes, as well as increased ultraviolet (UV) radiation and changes related to global warming. It is not expected that predicted temperature changes will have dramatic effects on the world's beaches by 2025, but the expected rise in sea level, if coupled with an increase in the frequency and/or intensity of storms, as predicted for some regions, is likely to lead to escalating erosion and consequent loss of habitat. It is suggested that increased UV radiation is unlikely to have significant effects. Increases in coastal human populations and tourism, thus increasing pressure on the shore, while serious, may be largely offset in developed and developing countries by better management resulting from greater understanding of the factors governing sandy-shore systems and better communication with beach managers and developers. Beach nourishment is likely to become more widely practised. However, the continuing hardening of surfaces in and above the dunes is bound to be damaging. Human pressures in many underdeveloped countries show no signs of being mitigated by conservation measures; it is likely that their sandy shores will continue to deteriorate during the first quarter of this century. A long-term trend that cannot be ignored is the excessive amount of nitrogen entering the sea, particularly affecting beaches in estuaries and sheltered lagoons. The data presently available and the uncertainty of a number of predictions do not permit of quantitative assessment or modelling of the state of the world's sandy shores by the year 2025, but some tentative, qualitative predictions are offered.
389 citations
Cites background from "Site selection by migratory shorebi..."
...For example, Botton et al. (1994) found that in Delaware Bay shorebirds (red knots, sanderling and ruddy turnstones) aggregated near shoreline discontinuities, including jetties that provided concentrating mechanisms for drifting Limulus eggs....
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TL;DR: This work documented the changes in body mass of shorebirds migrating through Delaware Bay and determined how much of the shorebird diet during this period consisted of horseshoc crab eggs.
Abstract: During spring migration, thousands of shorebirds gather in Delaware Bay at the same time as horseshoc crabs (Linudus polyphemus) are spawning. During their stopover, the birds store enough fuel in the form of fat and muscle protein to complete their migration to the Canadian breeding grounds. We documented the changes in body mass of shorebirds migrating through Delaware Bay and determined how much of the shorebird diet during this period consisted of horseshoc crab eggs. Migrating shorebirds were captured, morphometric measurements taken, and gut samples collected by stomach flushing. Red Knots (Calidris canutus). Ruddy Turnstones (Arenaria interpres), Sanderlings (C. alba), and Semipalmated Sandpipers (C. pusilla) increased their body mass up to 70-80% while staging on Delaware Bay. Horseshoe crab egg membranes constituted the bulk of the gut contents for all species at all collection sites. Polychaete and oligochaete worms were found in substantial concentrations in gut samples collected from shorebirds in certain beaches. Sand and unidentified decomposed material were found in varying amounts in gut samples of all species and locations. Apparent declines in spawning horseshoe crab populations may adversely affect migratory shorebirds.
181 citations
TL;DR: The role the horseshoe crab plays in the commercial fishery, in the biomedical industry, as well as for the shorebirds is discussed, and the economic impact the horsshoe crab has in the mid-Atlantic region is examined and the current developments of alternatives are reviewed.
Abstract: (2002). The Horseshoe Crab, Limulus polyphemus: 200 Million Years of Existence, 100 Years of Study. Reviews in Fisheries Science: Vol. 10, No. 1, pp. 39-73.
173 citations
Cites background from "Site selection by migratory shorebi..."
...This depth is beyond the reach of most shorebirds (Clark, 1996), but wave action and burrowing by spawning horseshoe crabs move some of the eggs toward the sand’s surface (Botton et al., 1994)....
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...According to Botton et al. (1994), staging areas serve as intermediate stopover points for the birds to feed before continuing their migration....
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TL;DR: The importance for comprehensive monitoring using robust survey designs is highlighted and research strategies needed to understand, value, and protect marine sedimentary ecosystems in the face of a rapidly changing environment are outlined.
168 citations
Cites background from "Site selection by migratory shorebi..."
...This, in turn, can increase aggregations of foraging shorebirds (Botton et al., 1994)....
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TL;DR: Body stores carried from the last spring staging area to the breeding grounds appear to offer Arctic-breeding shorebirds significant selective advantages: they are used for physical transformation from migration to breeding condition, and in years when weather is difficult may enable survival after arrival on the breeding Grounds.
Abstract: Severe summer weather in Greenland and Arctic Canada in 1972 and 1974 caused very poor breeding success and elevated adult mortality in red knots Calidris canutus islandica. We show that those individual knots that are known to have survived these summers were in better than average nutritional condition shortly before departure from their late spring staging area in west Iceland. The condition index of previously banded or subsequently recovered birds captured in Iceland was positively related to the number of summers they were known to have survived. Body stores carried from the last spring staging area to the breeding grounds appear to offer Arctic-breeding shorebirds significant selective advantages: they are used for physical transformation from migration to breeding condition, and in years when weather is difficult may enable survival after arrival on the breeding grounds.
141 citations
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TL;DR: The environmental conditions encountered during migration and the interactions with other individuals have evidently been important factors in the evolution of morphological and morphological differences among shorebird species.
Abstract: During migration, shorebirds form dense multispecific aggregations within rela- tively uniform and limited marine littoral habitats. The amount of available feeding space in the habitats frequented fluctuates widely with the daily and seasonal changes in the tidal rhythm. Shorebird species broadly overlap in their periods of peak abundance, inter- and intrahabitat distributions, and in the food organisms preyed upon. However, the totality of species differ- ences and the transient character of migratory assemblages apparently minimizes interspecific interactions that might result in competitive exclusion. The staggering of peak population densities and differences in distribution is most pronounced among morphologically similar species. The number of individuals and species that occur in an area is apparently determined by the amount of available feeding space and the physical diversity of the habitat. Food appears to be generally abundant relative to the requirements of the birds in all the habitats studied. The environmental conditions encountered during migration and the interactions with other individuals have evidently been important factors in the evolution of morphological and be- havioral differences among shorebird. species. Individuals must be as able to survive during the nonbreeding season as they are during the breeding season.
242 citations
TL;DR: Variation in shorebird distribution and abundance within microhabitats of the Mad River estuary, California, with the following null hypotheses was examined: shorebird spatial distribution was random, and no relationship existed between bird abundance and invertebrate densities.
Abstract: Spatial variation in the abundance of nonbreeding shorebirds can be predicted to varying degrees by the density of their prey species; strongest relationships obtain from studies encompassing large spatial scales (e.g., entire estuaries). We examined variation in shorebird distribution and abundance within microhabitats of the Mad River estuary, California, with the following null hypotheses: (1) shorebird spatial distribution was random, and (2) no relationship existed between bird abundance and invertebrate densities. Shorebirds exhibited nonrandom spatial distributions; species were highly clumped within the study area. Most foraging calidridine sandpipers (Calidris minutilla, C. mauri, and C. bairdii) aggregated in sandy areas within 1 m of the tide edge, where they foraged by probing for a burrow-dwelling amphipod, Corophium spp. By contrast, Semipalmated Plovers (Charadrius semipalmatus) and especially Ruddy Turnstones (Arenaria interpres) foraged by pecking in drier, coarse-grained substrates gmater than 1 m from the tide edge. Corophium densities in sand exceeded those in cobble; Corophium densities explained significant variation (r2 = 0.36, 0.31 and 0.22) in the abundance of Least Sandpipers, Western Sandpipers and all shorebirds, respectively. These findings emphasize the importance of understanding variation in processes across spatial scales.
180 citations
TL;DR: Study of assemblages of feeding shorebirds in three intertidal habitats on the coast of New Jersey during August to document how species segregate spatially both among and within habitats and to determine the effects of tidal cycles on these patterns.
Abstract: -We studied assemblages of feeding shorebirds in three intertidal habitats on the coast of New Jersey during August to document how species segregate spatially both among and within habitats and to determine the effects of tidal cycles on these patterns. The habitats were a sandy beach facing the ocean proper (outer beach), a sandy beach on the mainland side of a barrier island (inner beach), and a small mudflat adjacent to a Spartina alterniflora salt marsh. We were able to identify several microhabitats on the outer beach and mudflat. Most species fed in more than one habitat, but only two, Charadrius semipalmatus and Calidris canutus, used all three habitats regularly. Within habitats, most species exhibited strong preferences for the wettest areas, but we found differences among species in degrees of preference. The least amount of partitioning occurred on the inner beach, where birds crowded into a small zone near the water's edge and had frequent agonistic encounters suggesting intense competition. Shorebird feeding activity was partly a function of tide time: each habitat had a characteristic temporal pattern of use by shorebirds related to tide time rather than diel time; within habitats, we found species-characteristic feeding activity rhythms that were also a function of tide time. Feeding by most species peaked during the first 2 hours after low tide on the outer beach and mudflat. The results are discussed in terms of feeding strategies and interspecific competition.-Department of Biology, Livingston College, Rutgers University, New Brunswick, New Jersey 08903 (Burger, Chase); National Fish and Wildlife Laboratory, National Museum of Natural History, Washington, D.C. 20560 (Howe); and Institute of Animal Behavior, Rutgers University, Newark, New Jersey 07102 (Hahn). Present address of Chase: Department of Biology, Barnard College, New York, N.Y. 10027. Accepted 11 March 1977. (This paper was subsidized by the Migratory Bird Program, U.S. Fish and Wildlife Service.) ALTHOUGH usually solitary on their breeding grounds, migrating shorebirds (Charadrii) often form large, mixed-species aggregations that feed along coastal beaches, mudflats, and marshes. These concentrations of shorebirds result in high population densities in prime feeding areas (Recher and Recher 1969). As these habitats are effectively two-dimensional, spatial segregation of flock members can only occur in a horizontal plane. Increased density may lead to more intense competition for space, resulting in more frequent aggressive interactions and/or niche partitioning. Moreover the cyclic tidal inundation of mudflats and beaches causes changes both in the available feeding space and in the diversity and availability of prey items. Shorebirds respond to these changes by moving continually from one foraging area to another. Studies of ecology of migrating and wintering shorebirds have dealt primarily with feeding methods and rates (Goss-Custard 1969, Ashmole 1970, Burton 1972, Baker and Baker 1973, Baker 1974), feeding dispersions (Goss-Custard 1970a), prey densities (Bengtson and Svensson 1968, Brooks 1967, Goss-Custard 1970b), feeding ecology (Recher 1966, Thomas and Dartnall 1971, Holmes 1966, Holmes and Pitelka 1968), and aggressive behavior (Hamilton 1959, Recher and Recher 1969). Most of these studies stress behavior and diet as related to prey availability or broader ecological considerations. Collectively, most data suggest that shorebird species overlap broadly in their diets and feeding habitats. Competitive exclusion may be avoided because species move from point to point without fully exploiting the available food reserves (Recher 1966). Some studies have also identified patterns of niche partitioning with respect to foods, feeding methods, 743 The Auk 94: 743-758. October 1977 This content downloaded from 157.55.39.211 on Tue, 09 Aug 2016 05:06:27 UTC All use subject to http://about.jstor.org/terms 744 BURGER ET AL. [Auk, Vol. 94
175 citations