Shorebird Community Research Articles

A Ten Year Study of Variation, Trends and Seasonality of a Shorebird Community in the Mondego Estuary, Portugal

A monthly shorebird census in Mondego estuary, Portugal was made during ten years (1993-2002) and the information adds to the midwinter census carried out at international level. It is shown that higher variability in shorebird community occurred during the breeding and migrating periods, while the winter assemblage was very similar among years. The study provides precise information of the importance of the Mondego estuary, and the trends and phenology of its shorebird community. Six species are responsible for a large proportion of the total abundance throughout the year. Dunlin (Calidris alpina) is the most abundant species, followed by the Avocet (Recurvirostra avosetta). Over the study period, there was a significant increase in the total number of shorebirds that occur in some months. This was mainly due to the increase of the main species, the Dunlin. Only the Avocet showed a significant decrease in abundance. These trends were not explained by changes in overall flyway population or the Portuguese totals. Therefore, local explanations need to be considered (e.g., changes on habitat quality).

Patterns and determinants of shorebird species richness in the circumpolar Arctic

AbstractAim The intention with this study was first to investigate and describe the broad‐scale geographical patterns of species richness of breeding shorebirds (Charadriiformes; families: Charadriidae, Scolopacidae and Haematopodidae) throughout the arctic tundra biome. Secondly, after compensating for the positive relationship between net primary productivity (NPP) and species richness, the relative importance of additional ecological and historical variables for species richness was investigated. The main variables considered are NPP, length of snow‐ and ice‐free season, accessibility of regions depending on migratory flyway systems, tundra area at Pleistocene (120 and 20–18 ka bp) and Holocene (8 ka bp) times, and tundra area at present.Methods Information on shorebird species breeding distributions was compiled from distribution atlases and species accounts. The breeding distributions of shorebirds with ranges partly or completely in the Arctic (a total of 50 species) were mapped in ArcView 3.2 to create a raster grid layer of shorebird species richness at a 1° latitude × longitude resolution. The total and mean species richness value was calculated per each 10° of longitude sector of the Arctic. The relationships between species richness and the different climatic and environmental variables were analysed on the basis of this sector‐wise division of the arctic tundra. The influence of each variable on species richness was investigated using univariate and multivariate analyses (multivariate linear regression and general linear model).Results We found that patterns of breeding shorebird species richness in the Arctic tundra biome are to a large degree determined by the NPP, the length of the snow‐ or ice‐free season, the diversity of migratory flyways, as well as the historical extent of tundra habitat area during the maximum cooling of the last glacial period. Essentially, two main regions are distinguishable in the circumpolar Arctic regarding shorebird community richness. These are a species‐rich Beringia‐centred region and a species‐poor Atlantic‐centred region.Main conclusions The underlying explanations to these major trends may primarily be attributed to factors that operate at present through accessibility of areas from contemporary migration flyways, as well as processes that operated in the past during and after the last glacial cycle. The most prominent influence on the shorebird diversity was found for NPP in combination with the diversity of migratory flyways. These flyways provide the links between breeding and wintering resources, often separated by huge distances, and the geographical and ecological conditions associated with the shorebirds’ migration seem to be of particular importance for their breeding diversity in different sectors of circumpolar tundra.

Predicting site quality for shorebird communities: a case study on the Humber estuary, UK

The conservation importance of estuaries is often measured by bird numbers, but monitoring numbers is not necessarily a reliable way of assessing changes in site quality. We used an individual-based model, comprised of fitness-maximising individuals, to assess the quality of the Humber estuary, UK, for 9 shorebirds; dunlin Calidris alpina, common ringed plover Charadrius hiaticula, red knot Calidris canutus, common redshank Tringa totanus, grey plover Pluvialis squatarola, black-tailed godwit Limosa limosa, bar-tailed godwit L. lapponica, Eurasian oystercatcher Haematopus ostralegus and Eurasian curlew Numenius arquata. We measured site quality as predicted overwinter survival. The model accurately predicted the observed shorebird distribution (if non-starving birds were assumed to feed on any prey or patch on which intake rate equalled or exceeded their requirements), and the diets of most species. Predicted survival rates were highest in dunlin and common ringed plovers, the smallest species, and in Eurasian oystercatchers, which consumed larger prey than the other species. Shorebird survival was most strongly influenced by the biomass densities of annelid worms, and the bivalve molluscs Cerastoderma edule and Macoma balthica. A 2 to 8 % reduction in intertidal area (the magnitude expected through sea level rise and industrial developments) decreased predicted survival rates of all species except the dunlin, common ringed plover, red knot and Eurasian oystercatcher. This paper shows how an individual-based model can assess present-day site quality and predict how site quality may change in the future. The model was developed using existing data from intertidal invertebrate and bird monitoring schemes plus new intertidal invertebrate data collected over 2 winters. We believe that individual-based models are useful tools for assessing estuarine site quality.

Shorebird community variations indicative of a general perturbation in the Mont-Saint-Michel bay (France)

The Mont-Saint-Michel bay located on the East Atlantic Flyway is the first site in France for wintering shorebirds, with, on average, 53 000 individuals in January. Seven species represent 96% of that community: dunlin ( Calidris alpina), knot ( Calidris canutus), oystercatcher ( Haematopus ostralegus), curlew ( Numenius arquata), grey plover ( Pluvialis squatarola), bar-tailed godwit ( Limosa lapponica) and black-tailed godwit ( Limosa limosa). The international bird census organised by Wetlands International in mid-January gave us the opportunity to study, for a 23 years period, population variations in the bay. Despite a quite good carrying capacity, we showed that the decreasing proportion of 4 species in the bay relative to the other French populations may indicate a general perturbation of the bay. We discuss the different hypotheses to explain that observation. To cite this article: M.-C. Eybert et al., C. R. Biologies 326 (2003).

Winter Shorebird Communities and Tidal Flat Characteristics at Humboldt Bay, California

Abstract We examined winter (November–January) shorebird use at 19 sites around Humboldt Bay, California, an important site for nonbreeding shorebirds. We analyzed species richness (number of species), species densities, and incidences (presence/absence) in relation to habitat characteristics (tidal flat width, channelization, standing water, timing of tidal ebb, and sediment particle size). We included site area in analyses of incidence, and site area and substrate heterogeneity in the species richness analysis. We observed a total of 19 species, 8–16 at individual sites, and this variation correlated with substrate heterogeneity. Substrate particle size correlated positively with Sanderling (Calidris alba) incidence and negatively with American Avocet (Recurvirostra americana) incidence. Amount of standing water correlated positively with Whimbrel (Numenius phaeopus) and negatively with dowitcher (Limnodromus griseus and L. scolopaceus) incidence. Width of tidal flat correlated negatively with Whimbrel incidence. Sites at which tides ebbed earliest had higher incidences of Whimbrel and Sanderling and higher densities of Long-billed Curlew (Numenius americanus), but lower yellowlegs (Tringa melanoleuca and T. flavipes) densities. The amount of channelization correlated positively with curlew densities. These habitat relationships suggest that alteration of tidal flats at Humboldt Bay and elsewhere in coastal habitats has the potential to adversely affect patterns of shorebird distribution. Comunidades Invernales de Aves Playeras y Características del Plano Mareal en Humboldt Bay, California Resumen. Examinamos el uso invernal (noviembre–enero) de 19 sitios alrededor de Humboldt Bay, California, por parte de aves playeras. Ésta es un área importante para aves playeras no reproductivas. Analizamos la riqueza (número), densidad e incidencia (presencia/ausencia) de especies con relación a características del hábitat (ancho del plano mareal, canalización, agua estancada, momento de la disminución de la marea y tamaño de partículas del sedimento). Incluimos el área del sitio en los análisis de incidencia y el área del sitio y la heterogeneidad del sustrato en los análisis de riqueza de especies. Observamos un total de 19 especies (8–16 en sitios individuales), y esta variación se correlacionó con la heterogeneidad del sustrato. El tamaño de las partículas del sustrato se correlacionó positivamente con la incidencia de Calidris alba y negativamente con la de Recurvirostra americana. La cantidad de agua estancada se correlacionó positivamente con la incidencia de Numenius phaeopus y negativamente con la de Limnodromus griseus y L. scolopaceus. El ancho del plano mareal se correlacionó negativamente con la incidencia de N. phaeopus. Los sitios en que las mareas menguaron más temprano presentaron mayores incidencias de N. phaeopus y C. alba, y mayores densidades de Numenius americanus, pero menores densidades de Tringa melanoleuca y T. flavipes. El grado de canalización se correlacionó positivamente con las densidades de N. americanus. Estas relaciones de hábitat sugieren que la alteración de planos mareales en Humboldt Bay y en otros hábitats costeros potencialmente puede afectar adversamente los patrones de distribución de las aves playeras.

Habitat Use by Shorebirds at a Stopover Site in the Southern Great Plains

We studied habitat use of shorebirds (Charadriiformes) at a wetland experiencing natural fluctuations in water levels located at Tishomingo National Wildlife Refuge in the south-central Great Plains. We describe use of macrohabitats (disturbed, deciduous, snags, and mudflat) and microhabitats (dry-land, wet-land, and water) by foraging groups (terrestrial-aquatic gleaner, small aquatic prober-gleaner, aquatic gleaner). Water level was correlated with shorebird abundance. The small aquatic prober-gleaner group comprised 85.9% of the total shorebird community. Shorebirds selected mudflat macrohabitats (P < 0.05) and avoided disturbed, deciduous, and snags. All shorebird groups selected water microhabitat, except for the small aquatic prober-gleaner group that selected wet-land microhabitat (P < 0.05). There was a negative correlation (r s = -0.36, n = 58, P = 0.005) between pool level and number of shorebirds per survey. The relationship of water level and shorebird abundance may have more impact in an unmanaged wetland than managed wetlands. Tishomingo National Wildlife Refuge may be an important stopover site for small aquatic probes-gleaner species (e.g., western sandpipers, Calidris mauri) that require many stops along their migration routes.

SHOREBIRD DISTRIBUTIONS ON OCEAN BEACHES OF NORTHERN CALIFORNIA

Use of coastal beaches by nonbreeding shorebirds along the Pacific coast of North America is poorly understood because survey efforts have targeted large bays and wetlands where birds concentrate. Consequently, we studied coastal shorebird distributions and community composition by conducting monthly surveys at 40, 0.5-km linear plots along sandy beaches of coastal northern California from January through April 1996. We recorded 12 species, whose ranked abundances were consistent between winter (January–February) and spring (March–April). However, five of the six commonest species were more abundant in winter than spring. Among beaches, we detected a mean of 2.6 ± 2.3 (SD; range: 0–9) species and 12.0 ± 14.1 (range: 0–62) individuals. Number of species correlated positively with total shorebird abundance. Most species' abundances varied greatly among sites; nine taxa had aggregated spatial distributions, one species was hyper-dispersed, and two species were randomly distributed among beaches. Species composition of the shorebird community was highly nested, partly because abundant species were more widespread in their occurrence than less-numerous taxa. More species and individuals occurred at sites near Humboldt Bay, probably because high tides forced birds off their principal feeding areas within the bay to adjacent beaches. Variation in shorebird use of beaches suggests that some areas are more important to wintering and migrating shorebirds than other locations. Although current levels of human activity in coastal northern California do not appear to influence distributions of nonbreeding shorebirds, we suggest that monitoring and management plans be considered to minimize potential negative impacts of recreational activities, which are certain to increase with human population size and recreational use of beaches.

Shorebird Community Patterns in a Seasonally Dynamic Estuary

I examined the influence of environmental factors (exposed intertidal habitat, river volume and invertebrate abundance) on nonbreeding shorebird communities in the Mad River, California, an estuary in which intertidal habitats are affected by seasonal variation in river discharge. The shorebird community exhibited the following temporal (July-April) variation: (1) species composition exhibited a 50% turnover between October and November; (2) species richness peaked in summer, declined in winter and increased in spring; (3) shorebird abundance peaked in summer, when most birds foraged in cobble habitats; and (4) during winter a large percentage of birds roosted, and a small proportion fed in low numbers in aquatic habitats. Exposed intertidal habitat explained significant variation in both community patterns and the abundance of five species; these species were characterized by use of exposed intertidal habitats. Compared with other studies, the relatively weak associations between environmental variables and variation in the shorebird assemblage suggests that shorebirds occupying seasonally dynamic estuaries may exhibit space use and activity patterns different from those reported for birds occupying coastal estuaries where habitat availability and food resources are more predictable.

Shorebird Communities on British Estuaries: Factors Affecting Community Composition

Environmental gradients across 109 British estuaries were examined in relation to the communities of shorebirds in winter. Ordination and classification techniques were employed on the 5-year means of peak-winter high-tide counts for the 13 most common species, converted to densities, for the two periods, 1969-75 (first period) and 1981 -85 (second period), in order to quantify changes in community composition between the two periods. Multiple regression within GLIM was then used to relate the DCA ordination scores to physical, climatic, geographic and water chemistry variables. In an ordination analysis of the combined data for the two periods, axis 1 had a left-right gradient of species favouring coastal lagoons (avocet) to those favouring sandy estuaries (bar-tailed godwit, sanderling, knot)

Eulimdana lari (Yamaguti, 1935) n. comb. (Nematoda: Filarioidea) from Phalaropus spp. (Charadriiformes) in Canada and a review of the genus Eulimdana Founikoff, 1934

Eulimdana lari (Yamaguti, 1935) n. comb. (Nematoda: Filarioidea) was found in 1 of 26 Phalaropus lobatus (L.) and 3 of 9 P. tricolor (Vieillot) collected in Canada near Deer Island, New Brunswick, and Delta, Manitoba, respectively. This is the first report of the parasite in the New World and extends the distribution of the parasite across the Holarctic. Eulimdana lari is now known from 17 species of Charadriiformes, including P. tricolor which is a new host record. It is suggested that E. lari is a parasite of shorebird communities. Eulimdana lari is redescribed and a taxonomic review of Eulimdana Founikoff, 1934 is provided, including an amended generic diagnosis and an annotated list of the five species. Heimnema Chabaud, Brygoo, and Richard, 1964 is placed in synonymy with Eulimdana. In addition to E. lari (Yamaguti, 1935) n. comb., the following changes are made: E. micropenis (Travassos, 1926) n. comb. and E. heimi (Chabaud, Brygoo, and Richard, 1964) n. comb. Eulimdana mazzantii (Railliet, 1893) Neveu-Lemaire, 1936, is considered a species inquirenda. It is pointed out that the type species, E. clava (Wedl, 1856) Founikoff, 1934 has a worldwide distribution in pigeons.

Interspecific Aggression and the Limiting Similarity of Close Competitors: The Problem of Size Gaps in Some Community Arrays

Starting from MacArthur's hypothesis that interspecific aggression will occur whenever one of the species can expect to gain from this behavior, a model is built explicating the circumstances under which the limiting size similarity cannot be expected to be solely caused by resource competition. We develop the model from considerations of shorebird and waterfowl communities which inhabit open defensible terrain and in which gaps occur in the sequence of size similarities. In shorebird communities there exists a gap of two or three species between the cranes and the sandpipers; in waterfowl communities the gap is three species. In both communities natural history data suggest that interspecific aggression by the largest member of the sequence has eliminated intermediate sized species. Similar gaps do not occur in the rail-heron community, which inhabits an indefensible habitat.

SHOREBIRDS OF COASTAL BUENOS AIRES PROVINCE, ARGENTINA

SUMMARYThe Pampas shorebird community is comprised of species from diverse taxonomic and faunal origin. Four major groups can be recognized: North American migrants residing in coastal Buenos Aires Province during their non‐breeding season, Patagonian species wintering locally but breeding further south, Pampean species breeding locally, and Brazil–Paraguayan species present during their breeding season. Because of differences among these groups in the timing and migration patterns, community composition shows marked seasonal variation. Both nesting and non‐breeding birds use a diversity of habitat types ranging from littoral sandy beaches to upland grasslands. Throughout the year, however, and in all habitat types, non‐breeders predominate in species number and abundance. Intra‐ and inter‐specific patterns of aggression suggest both that resources are limiting, and that non‐breeding migrants may play an important role in determining breeding community composition.

Shorebird Food Habits in the Eastern Canadian Arctic

documented for six species of this shorebird community (Baker and Baker 1973). Here, I examine the community from the point of view of the relationships between shorebird body size and food size. I also consider the degree of species distinctness along the food size parameter of the niche in relation to the theory of species packing. Data on food size and body size are examined in view of the hypothesis that larger species of shorebirds consume larger average prey and are more selective foragers than small species (Baker and Baker 1973). The hypothesis resulted from the discovery that within a community of six species, the heavier species foraged more slowly (number of prey capture attempts per unit time). To maintain a caloric intake higher than that required by a smaller species (Nice 1938), larger shorebirds may select larger food items and thus may require more time to find each item in the array of food items of different size.