Arenaria Interpres Research Articles

Intestinal Helminths of Fall-Migrating Ruddy Turnstones, Arenaria interpres (L.), from New Brunswick, Canada, with a Checklist of Helminths Reported from this Host

Nine species of helminths (5 trematodes and 4 cestodes) were recovered from 10 (3 adults, 7 juveniles) ruddy turnstones, Arenaria interpres, collected from a marine habitat on Miscou Island in New Brunswick, Canada, during fall migration in August of 2003. The number of helminths per bird ranged from 24 to 36,217 individuals; the number of helminth species per bird ranged from 3 to 6. The parasite taxa were typically distributed, with 2 or 3 species predominant and the remaining species making up a relatively small proportion of the total. The cestode Anomotaenia clavigera was the most prevalent helminth; the trematodes Microphallus papillorobustus and Maritrema subdolum were the most abundant helminths, together accounting for 94.6% of all helminths recovered. This study is the first to examine the helminth parasites of turnstones during fall migration. A checklist of helminth parasites previously reported from the ruddy turnstone is included.

HELMINTH COMMUNITIES OF THREE SYMPATRIC SPECIES OF SHOREBIRDS (CHARADRII) FROM FOUR SUMMER SEASONS AT BRISTOL BAY, ALASKA

Helminth communities in sympatric black turnstones (Arenaria melanocephala), ruddy turnstones (Arenaria interpres), and dunlin (Calidris alpina) were examined over 4 summers in Bristol Bay, Alaska. The compound community, made up of component communities of all 3 species of hosts for 4 summer seasons (n=164), consisted of 43 helminth species, with cestodes, especially Anomotaenia clavigera, accounting for 47% of the helminth species and 95% of the abundance. The black turnstone had significantly higher species richness and abundance than either the ruddy turnstone or dunlin. The congeneric black and ruddy turnstone component communities were the most similar, and the dunlin's was the least similar. New helminth species continued to be acquired in all 3 host species during years 2 to 4. There was no significant difference for abundance among sample years for each of the 3 species of host. The 3 component communities all included a predictable suite of helminths with 1 dominant species and 4 to 5 associates, a large number of less-predictable species, and a greater prevalence and abundance of cestode species. Consistencies over time included high diversity, low evenness, low species richness (<5), and continued recruitment of small numbers of helminth species with low prevalence and abundance. There was minimal circulation of helminth species between the dunlin and the 2 turnstone species, indicating a considerable degree of specialization, particularly among species of cestodes.

Stable isotope and pen feeding trial studies confirm the value of horseshoe crab Limulus polyphemus eggs to spring migrant shorebirds in Delaware Bay

We used stable isotope (SI) methods in combination with pen feeding trials to determine the importance of eggs of the Atlantic horseshoe crab Limulus polyphemus to migratory fattening of red knots Calidris canutus rufa and ruddy turnstones Arenaria interpres morinella during spring stopover in Delaware Bay. By manifesting measurable fractionation (ca +3‰) and rapid turnover, blood plasma δ15 nitrogen proved a functional marker for SI diet tracking during the short 3‐week stopover. Blood samples from free‐ranging knots (3 data sets) and turnstones (1 data set) produced similar convergence of plasma δ15N signatures with increasing body mass that indicated highly similar diets. Asymptotes deviated slightly (0.3‰ to 0.7‰) from that of captive shorebirds fed a diet of only crab eggs during stopover, thus confirming a strong crab egg‐shorebird linkage. The plasma δ15N crab‐egg diet asymptote was enriched ca +4.5‰ and therefore readily discriminated from that of either blue mussels Mytilus edulis or coquina clams Donax variabilis, the most likely alternative prey of knots in Delaware Bay. Crab eggs were highly palatable to captive knots and turnstones which achieved rates of mass gain (3–11 g/d) comparable to that of free‐ranging birds. Peak consumption rates during hyperphagic events were 23,940 and 19,360 eggs/bird/d, respectively. The empirical conversions of eggs consumed to body mass gained (5,017 eggs/g for knots and 4,320 eggs/g for turnstones) indicate the large quantities of crab eggs required for the maintenance of these shorebird populations during stopover.

The breeding ecology of ruddy turnstones (Arenaria interpres) in the eastern Canadian Arctic

In 2002 and 2003, studies were made of the breeding phenology, nesting success, nesting density, and rates of nest predation of ruddy turnstones (Arenaria interpres) at East Bay, Southampton Island, Nunavut, Canada. Previous data from East Bay were used to compare nesting chronology and nest success across years. Bird banding data were used to examine migration routes and rates of return. In all years, ruddy turnstones initiated nests within 7 days of arrival at the study area. The median date of incubation onset was the same in 2002 and 2003, despite different spring snow conditions. Snow remained later in the season in 2003 and the overall range of incubation onset was greater than in 2002. Ruddy turnstones at East Bay nested at high densities and in semi-colonial groups with a significantly aggregated distribution. In both years, nest success was low, predation was high, and lemmings were scarce. These data (and data from earlier East Bay studies) support the ‘alternative prey hypothesis’. Resighting rates of breeding adults between 2002 and 2003 were also low. Individuals banded at East Bay were resighted at Delaware Bay on the Atlantic coast of the United States, the Caribbean Islands, and in southern Brazil. This study increases our knowledge of this understudied species about which there is conservation concern.

Molecular Epidemiologic Studies on North American H9 Avian Influenza Virus Isolates from Waterfowl and Shorebirds

Because sequence data on H9 avian influenza virus (AIV) from wild birds are currently limited, we set out to determine the sequence of the hemagglutinin (HA) gene of H9 viruses circulating in North American waterfowl and shorebirds. In this study, we examined the HA gene from H9 AIV isolated from mallards (Anas platyrhynchos) sampled during 1998 and 1999 in Minnesota and ruddy turnstones (Arenaria interpres) sampled during 2003 in Delaware and New Jersey. At these sites, the H9N2 subtype represented 12% and 4% of the avian influenza isolates from mallards in 1998 and 1999, respectively, and 8% of the AIVs isolated from shorebirds between 2000 and 2002. Sequences from these viruses were compared with sequences from H9 AIV isolated from commercial poultry and aquatic birds from North America, Europe, Asia, and the Middle East: four previously reported and three new clades were observed. Sequence data from the HA gene of North American waterfowl and shorebird isolates generated in this study most closely group with the Eurasian H9 viruses in the Y439 clade. In addition, the HA cleavage site (AASNR/G) and receptor binding site was identical to the representative virus of that group (DK/Hong Kong/Y439/97). Viruses in that clade are commonly found in ducks and chickens in Hong Kong and Korea. Positive evolutionary selection (dNonsynonymous > dSynonymous) was observed for the HA gene among the North American waterfowl and shorebird H9N2 viruses, indicating that the H9N2-type viruses are changing in their natural hosts.

Effects of Nest Habitat, Food, and Parental Behavior on Shorebird Nest Success

AbstractAbstractIn environments such as arctic tundra, where bird densities are low and habitats are comparatively homogeneous, suitable nest sites likely are not limited. Under these conditions, reproductive success of birds may be determined by factors other than the habitat characteristics of nest sites. We studied the relative influence of nest habitat, food, nest distribution, and parental behavior on the reproductive success of tundra-breeding shorebirds at East Bay, Southampton Island, Nunavut, Canada. From 2000 to 2002, we monitored the nests of five species: Black-bellied Plover (Pluvialis squatarola), Semipalmated Plover (Charadrius semipalmatus), Ruddy Turnstone (Arenaria interpres), White-rumped Sandpiper (Calidris fuscicollis), and Red Phalarope (Phalaropus fulicarius). For each species, habitat differed between nest sites and random sites. In contrast, habitat differed between successful and failed nest sites only for White-rumped Sandpipers. Shorebirds did not prefer to nest in habitats where food was most abundant. Although nest success varied among species in all years, artificial nest experiments suggested that interspecific variation in predation rate was not related to habitat type. Instead, the marked interspecific variation in nest success may have been related to incubation behavior. Species taking fewer incubation recesses had higher nest success, although these results should be viewed as preliminary. The factor with the greatest interannual influence on nest success was fluctuating predation pressure, apparently related to the abundance of predators and lemmings.

EFFECTS OF NEST HABITAT, FOOD, AND PARENTAL BEHAVIOR ON SHOREBIRD NEST SUCCESS

Abstract ABSTRACT In environments such as arctic tundra, where bird densities are low and habitats are comparatively homogeneous, suitable nest sites likely are not limited. Under these conditions, reproductive success of birds may be determined by factors other than the habitat characteristics of nest sites. We studied the relative influence of nest habitat, food, nest distribution, and parental behavior on the reproductive success of tundra-breeding shorebirds at East Bay, Southampton Island, Nunavut, Canada. From 2000 to 2002, we monitored the nests of five species: Black-bellied Plover (Pluvialis squatarola), Semipalmated Plover (Charadrius semipalmatus), Ruddy Turnstone (Arenaria interpres), White-rumped Sandpiper (Calidris fuscicollis), and Red Phalarope (Phalaropus fulicarius). For each species, habitat differed between nest sites and random sites. In contrast, habitat differed between successful and failed nest sites only for White-rumped Sandpipers. Shorebirds did not prefer to nest in habitats w...

Shorebird roost‐site selection at two temporal scales: is human disturbance a factor?

Summary Roost‐site selection in shorebirds is governed by ambient factors, including environmental conditions and human disturbance. Determination of the extent to which these factors affect roost use and the associated implications for shorebird habitat protection is important for conservation strategies and informed management of human recreational use of these habitats. Shorebird conservation as a whole is a high priority world‐wide because a large proportion of shorebird species is in decline. However, little is understood about the consistency of roost use by different species, what conditions affect species‐specific roost‐site selection, and at what spatial and temporal scales conditions influence selection. We studied high‐tide roost‐site selection by eight species of non‐breeding shorebirds on a critically important stopover and wintering refuge. We calculated spatial and temporal variability in roost use for each species based on counts and consistency of incidence. We then examined roost‐site selection in relation to structural, environmental and human disturbance factors, and how this varied across spatial and temporal scales. Most roosts were used less than 50% of the time, although larger roosts were used more consistently. This varied among species, with red knot Calidris canutus tending to concentrate at a few roosts and American oystercatcher Haematopus palliatus, dowitcher Limnodromus griseus and Limnodromus scolopaceus and ruddy turnstone Arenaria interpres more diffusely distributed among roosts. At an annual scale, the principal factors affecting shorebird presence at roosts were roost length (size), local region, substrate and aspect. The extent and direction of these effects varied among species. Among years, red knots avoided roosts that had high average boat activity within 1000 m, but disturbance did not appear to be a factor for other species. Daily roost use was influenced primarily by wind speed and the ability of roosts to provide shelter from the wind. Only dowitchers appeared to track daily disturbance, avoiding prospective roosts when boat activity within 100 m was high. Synthesis and applications. Our findings emphasize the need to consider species‐specific differences in temporal‐ and spatial‐scale effects of roost‐site selection factors, including human disturbance, when employing conservation measures for shorebirds. We suggest that conservation management should aim to provide a wide range of potential roosts (both natural and artificial) that could be used under different wind conditions and that are within reasonable travelling distance of preferred feeding areas. Roost use is often highly variable, and monitoring efforts must take this into account before making inferences about changes in use or selection of roost sites.

Differences in food abundance cause inter-annual variation in the breeding phenology of High Arctic waders

Previous work has shown that High Arctic waders in Greenland are “income breeders”, i.e. the resources used for egg formation are based almost entirely on biomass obtained on the breeding grounds. Thus, their breeding phenology is expected to be highly sensitive to inter-annual variation in food abundance during the pre-laying period. Early spring snow-cover may also influence timing of egg-laying either directly or mediated through food resources. Here, we report on the inter-annual variation in clutch initiation of three wader species breeding in High Arctic Greenland, Sanderling (Calidris alba), Dunlin (Calidris alpina) and Ruddy Turnstone (Arenaria interpres), in relation to spring snow-cover and spring arthropod abundance over ten breeding seasons at Zackenberg Research Station 1995–2005. Food abundance had the strongest effect on timing of clutch initiation, while the proportion of snow-free land had a weaker but still significant effect, i.e. more food and more snow-free land both result in earlier egg-laying. We hypothesize that food is most important when there is sufficient snow-free land to nest on, while snow-cover is of increasing importance in years with late snowmelt.

Abundância sazonal de aves migratórias na Área de Proteção Ambiental de Piaçabuçu, Alagoas, Brasil

Every year, thousands of limicola and migratory birds winter on the South American coast, between September and April, where they acquire body mass and undergo moulting before returning to their reproduction sites. Qualitative and quantitative studies were performed in the Piacabucu Protection Area located in the state of Alagoas, Brazil, by direct counting, aiming to follow upon the birds’ seasonal migration. Five species of Charadriidae family were recorded: Vanellus chilensis (Wagler, 1827); Pluvialis squatarola (Linnaeus, 1758); Charadrius semipalmatus Bonaparte, 1825; Charadrius collaris Vieillot, 1818 and Charadrius wilsonia (Ord, 1814), and five of the Scolopacidae family: Arenaria interpres (Linnaeus, 1758); Actitis macularius (Linnaeus, 1766); Catoptrophorus semipalmatus (Gmelin, 1789); Calidris pusilla (Linnaeus, 1766) and Calidris alba (Pallas, 1764). Pluvialis squatarola, Charadrius semipalmatus, Charadrius collaris, Arenaria interpres, Calidris pusilla and Calidris alba were considered constant (present in over 50% of observation time). Charadrius semipalmatus and Calidris alba showed highest level of frequency during November and December and March and September, respectively. Spearman correlation shows a strong dependency on migration of this species. The birds’ loyalty to the Piacabucu area seen in this research show that this is a preferred site for wintering thus reinforcing its importance for the conservation of the migratory species that utilize the site.

Ruddy turnstones Arenaria interpres rapidly build pectoral muscle after raptor scares

To cope with changes in the environment, organisms not only show behavioural but also phenotypic adjustments. This is well established for the digestive tract. Here we present a first case of birds adjusting their flight machinery in response to predation risk. In an indoor experiment, ruddy turnstones Arenaria interpres were subjected to an unpredictable daily appearance of either a raptor or a small gull (as a control). Ruddy turnstones experiencing threat induced by a flying raptor model, longer than after similar passage by the gull model, refrained from feeding after this disturbance. Pectoral muscle mass, but not lean mass, responded in a course of a few days to changes in the perceived threat of predation. Pectoral muscle mass increased after raptor scares. Taking the small increases in body mass into account, pectoral muscle mass was 3.6% higher than aerodynamically predicted for constant flight performance. This demonstrates that perceived risk factors may directly affect organ size.

Variation in the innate and acquired arms of the immune system among five shorebird species

To contribute to an understanding of the evolutionary processes that shape variation in immune responses, we compared several components of the innate and acquired arms of the immune system in five related, but ecologically diverse, migratory shorebirds (ruff Philomachus pugnax L., ruddy turnstone Arenaria interpres L., bar-tailed godwit Limosa lapponica L., sanderling Calidris alba Pallas and red knot C. canutus L.). We used a hemolysis-hemagglutination assay in free-living shorebirds to assess two of the innate components (natural antibodies and complement-mediated lysis), and a modified quantitative enzyme-linked immunosorbent assay in birds held in captivity to assess the acquired component (humoral antibodies against tetanus and diphtheria toxoid) of immunity. Ruddy turnstones showed the highest levels of both innate and acquired immune responses. We suggest that turnstones could have evolved strong immune responses because they scavenge among rotting organic material on the seashore, where they might be exposed to a particularly broad range of pathogens. Although ruffs stand out among shorebirds in having a high prevalence of avian malaria, they do not exhibit higher immune response levels. Our results indicate that relationships between immune response and infection are not likely to follow a broad general pattern, but instead depend on type of parasite exposure, among other factors.

Increased nest predation in a declining and threatened Temminck's Stint Calidris temminckii population

We measured nesting success of the Temminck's Stint Calidris temminckii along the Finnish Bothnian Bay coast during 19 breeding seasons (1983–2001) and conducted a population census (1999–2002). We found 105 pairs, showing a marked decline from the previous survey (170 pairs 1987–95). Of the 424 ‘known‐fate’ nests, 47% hatched. Depredation caused 79.9% of the nest losses. Nesting failures increased from 1983–91 to 1992–2001 owing to a rise in nest predation. The proportion of failed nests that failed because of predation rose from 48.9 to 87.7%. When only depredated nests were considered as losses, Mayfield nest survival probability over the incubation period dropped from 69 to 31% (461 nests). This pattern emerged both in man‐made and in natural habitats. Survival probability was independent of habitat type (natural vs. man‐made). In an experiment involving videotaping of dummy nests, Common Gull Larus canus and Ruddy Turnstone Arenaria interpres were found to be the most important egg predators.

The mechanisms of interference competition: two experiments on foraging waders

Models of population dynamics that include interference competition have often been applied to foraging waders and less so to other foragers, even though these models are, in principle, generally applicable. At present, however, it is still unclear whether interference competition is of importance for foraging waders. To support this idea experimental evidence and knowledge of the mechanisms underlying interference effects are required. We experimentally determined the relationship between forager density and foraging success in two wader species: the red knot (Calidris canutus) and the ruddy turnstone (Arenaria interpres). With each of the two species, we conducted an experiment consisting of 300 one-min trials. In these trials we scored the behavior and the foraging success of focal individuals at specific combinations of bird and prey density. Irrespective of prey density, individuals of both species discovered fewer prey items at higher bird densities. Despite this, only in turnstones did intake rates decline with increasing bird density. Knots compensated for a lower prey-discovery rate by rejecting fewer prey items at higher bird densities. In knots, bird density had a complex, nonmonotonic effect on the time spent vigilant and searching. In turnstones the main effect of increased bird density was a reduction in the prey-encounter rate, that is, the reward per unit search time. Effects on the time spent vigilant and the time spent searching were less pronounced than in knots. Thus, the mechanistic basis of the effects of bird density was complex for each of the two species and differed between them. Key words: Arenaria interpres, behavioral mechanisms, Calidris canutus, density dependence, exploitation competition, social dominance. [Behav Ecol]

Spatial clumping of food and social dominance affect interference competition among ruddy turnstones

In studying the success of foraging animals, studies of interference competition have put emphasis on effects of competitor density, whereas studies of resource defense have focused on the effects of the spatial distribution of food within patches. Very few studies have looked at both factors simultaneously, that is, determined whether the effects of competitor density on foraging success depend on the spatial distribution of food. We studied the behavior and the foraging success of ruddy turnstones (Arenaria interpres) using an experiment in which we varied both the presence of a competitor and the food distribution. Because turnstones may differ strongly in their relative dominance status, we also experimentally varied the foragers’ relative dominance status. We found that the presence of a competitor only reduced the foraging success of subordinate birds foraging at the clumped food distribution. At this condition, dominant and subordinate birds differed markedly in their foraging success. Contrary to our expectations, we did not observe more agonistic behavior at the clumped food distribution. This indicates that the amount of agonistic behavior observed may be a bad indicator of interference effects. These findings have specific implications for models of interference competition. Most notably they show that the effects of competitor density on agonistic behavior and foraging success may well depend on the spatial distribution of food and the foragers’ relative dominance status. Additionally, our results suggest that social dominance will not be fully understood without considering long-term processes such as the formation and maintenance of social dominance hierarchies. Key words: agonistic interactions, Arenaria interpres, density dependence, foraging behavior, foraging experiment, resource defense. [Behav Ecol]

Migration patterns, population trends and morphometrics of Ruddy Turnstones Arenaria interpres passing through Ottenby in south-eastern Sweden

We analysed 57 years’ uninterrupted trapping data of autumn migrating Ruddy Turnstones Arenaria interpres at Ottenby, south-eastern Sweden (1593 full-grown birds in 1947–2003; of them 574 birds with standardised trapping in 1976–2003). Numbers trapped decreased significantly for both adult and juvenile birds in the total dataset (–0.34 and –0.57 ringed birds per year), and for juveniles in the 1976–2003 dataset (–0.51 per year). Median date for adults was 27 July and for juveniles 6 August. Adult females passed on average three days earlier than adult males (females 27 July, males 30 July). The mean body masses (juveniles 108.0 g, adults 108.4 g) correspond to a fuel load of 21–22% in relation to lean body mass (89 g). Length of stay of retrapped birds was only 3.6 days. Thus, they continued the migration with small to moderate fat loads, comparable to reported fat loads elsewhere. Forty-four recoveries illustrate a narrow migration route along the western coasts of Europe, south to the wintering areas in tropical West Africa.

Predicting the effects of marine climate change on the invertebrate prey of the birds of rocky shores

By the end of the 21st century models of climate change predict that the air temperature over most of the British Isles will increase by between 2 and 3 °C and sea‐level will rise by 40–50 cm. Over that period it will become windier and mean wave height will increase, as will the frequency of storms. These changes in climate and weather will impact the intertidal zone of the UK and will cause distribution changes in many of the common invertebrate species that live there. Where these changes are severe they may well impact on patterns of distribution of ducks and wading birds. In the British Isles a number of organisms live close to their geographical limits of distribution. Some of these species might be expected to extend their range as climatic restraints are relaxed. Species currently limited by cool summers or winter cold will move northwards. In most cases the effects on the distribution of waterbirds will be small. For example, the replacement of the Northern Limpet Patella vulgata by the Southern Limpet P. depressa is unlikely to adversely affect Eurasian Oystercatchers Haematopus ostralegus. Of wider concern is the possibility that as climate warms the abundance and productivity of brown algae will decrease. This is likely to have two significant effects for waders. First, it would represent a loss of potentially rich feeding grounds for species such as Ruddy Turnstone Arenaria interpres that feed on small easily desiccated invertebrates living on or below the seaweed. Secondly, as algae die or are broken away the resulting debris is exported to sediment habitats where it considerably boosts the in situ production of bacteria at the base of the food web. An increase in sea‐level will only have a major impact on the extent of rocky shore invertebrate communities where shore topography prevents the upward migration of the biota. Where a seawall limits shores, for example, biological production will be curtailed as the area available for colonization decreases. Increases in the size of waves and the frequency of storms will mimic increasing exposure and there will be a significant reduction in algal production in areas that are affected.

The possible impact of climate change on the future distributions and numbers of waders on Britain's non‐estuarine coast

The relationship between weather and wader distributions on non‐estuarine coasts is described and used to predict how future wader distributions may respond to climate change. The distributions of eight out of nine species of wader commonly wintering on the non‐estuarine coasts of Britain altered between two similar surveys, in 1984/85 and 1997/98, that covered 78% and 38% of Britain's 12 594 km of non‐estuarine coastline, respectively. These eight species moved at least in part either eastwards along the winter isotherms or northwards. These changes in distribution broadly coincide with a distributional shift towards the species’ respective breeding grounds and are correlated with the local winter weather over the period: increasingly mild extreme temperatures and changes in mean rainfall, mean wind speed and wind‐chill. Based on the scenarios for Britain's climate in 2020 and 2080, it is predicted that the distributions of the waders will move away from the west. The non‐estuarine coasts of Britain hold particularly high proportions of the international flyway populations of Ringed Plover Charadrius hiaticula, Sanderling Calidris alba, Purple Sandpiper Calidris maritima and Ruddy Turnstone Arenaria interpres that are all expected to show continuing decline to 2080. Overwintering waders appear to be good indicators of the effects of climate change.

Prey abundance and habitat use by migratory shorebirds at coastal stopover sites in Connecticut

Stopover areas are vital for the successful migration of many species of shorebirds, as they, in part, allow individuals to deposit large quantities of fat needed to fuel their northward and southward journeys. While much research has focused on bird migration, few studies closely examine the environmental characteristics of specific stopover areas. For our study, we conducted prey availability surveys and documented shorebird habitat use during northward summer migration for three historically important stopover areas along the Connecticut Long Island Sound coastline in 2000. Coastal Connecticut provides important habitat not only for shorebirds migrating from northern Canada to South America, but also for resident breeding shorebirds (e.g., oystercatchers, plovers, and sandpipers). Our prey availability surveys indicate that all three stopover sites were characterized by some combination of polychaete worms, crustaceans, and mollusks. Polychaete worms of the family Neredidae were the most common prey item at two of the three sites. In addition, the site frequented by the greatest densities of shorebirds also had the greatest density of nereid worms and the greatest diversity of invertebrates. In terms of habitat use, our results indicate that foraging densities tended to be highest on intertidal habitats that were sheltered from coastal wave action and where densities of benthic (burrowing) and epifaunal (surface-dwelling) prey tended to be high. However, some shorebird species, including one breeding resident, the American Oystercatcher (Hae- matopus palliatus) and one migrant, the Ruddy Turnstone (Arenaria interpres), both of special management concern, favored foraging on beach-front habitats. In contrast to foraging habitat preferences, shorebirds roosting at high tidal phases showed strong preferences for beach habitats fronting the Long Island Sound. The use of beach-front habitats for both foraging and roosting poses a challenging situation for beach managers.

Environmental heterogeneity, spatial segregation of prey, and the utilization of southwest Atlantic mudflats by migratory shorebirds

We studied the relationships between the habitat use of migratory shorebirds and the spatial distributions of the Southwestern Atlantic Fiddler Crab Uca uruguayensis, polychaetes, sediment characteristics and tidal levels in the Río de La Plata estuary, Argentina, where U. uruguayensis is one of the most important intertidal species. Crabs have a well‐defined patchy distribution that is segregated spatially from that of polychaetes. Crab density on the surface varied across the tidal cycle, reaching maximum values during low tide. Polychaete density decreased with depth but showed no change through the tidal cycle; however, given that sediment penetrability did change during the same period, their availability to probing shorebirds is expected to change. Habitat use by shorebirds followed the spatial distribution of prey; shorebirds that foraged on polychaetes (White‐rumped Sandpiper Calidris fuscicollis, Two‐banded Plover Charadrius falklandicus and Hudsonian Godwit Limosa haemastica) focused their attention on the areas with the highest densities of polychaetes, whereas species that preyed mostly on crabs (Ruddy Turnstone Arenaria interpres, Whimbrel Numenius phaeopus and Grey Plover Pluvialis squatarola) predominantly used areas with crabs. This segregation occurred particularly during low tide, a period in which polychaetes became fully available. Results show that the spatial and temporal heterogeneity of mudflats in relation to the types and availability of prey has a strong effect on shorebird habitat use.