Centre for Ecology and Evolution

In the course of each spring, two subspecies of knots Calidris canutus (islandica wintering in Europe and breeding in the Nearctic, and canutus wintering in west Africa and breeding in Siberia), stage in the international Wadden Sea before their northward flights to the arctic breeding grounds. In March-April islandica-knots predominantly use the intertidal flats in the western part of the Wadden Sea in The Netherlands (canutus is still in west Africa). In May both subspecies use the eastern part of the Wadden Sea in Schleswig-Holstein, Germany only. We studied these knots in core areas at both ends of the Wadden Sea in 1990, to examine whether the absence of knots in the western Wadden Sea in May is related to food res6urces or to other factors connected with the energy budget of these long-distance migrants. Islandica-knots in March-April in The Netherlands and canutus-knots in May in Germany had similar diets and showed similar size selection of their major bivalve prey Macoma balthica, giving the possibility for indirect competitive interactions. Knots spent more time feeding per day in Germany. The harvestable biomass of Macoma was of comparable magnitude in both parts of the Wadden Sea in May. That knots always leave the western Wadden Sea in late April is, therefore, not a direct response to prey depletion. If Macoma always subsides earlier in the year in the western part of the Wadden Sea than in the east as in 1990, the knots' absence in the west may represent the riding of an eastward wave of good feeding conditions resulting from longitudinal variation in bivalve-prey biology. At least for canutus, the reliance in May on the eastern Wadden Sea may (additionally?) represent early movements - at relatively low body masses - towards the breeding areas to gain the benefits of a small saving on the cost and time of travel, and of being closer to the weather systems that may help their flight into the breeding areas

We studied the food and feeding ecology of Red Knots Calidris canutus rufa on an area of rocky flat, or restinga, near San Antonio Oeste in the northwest of Golfo San Matias, Provincia de Rio Negro, Argentina in March 1992. These Red Knots are on their way north, from "wintering" areas in Tierra del Fuego (Argentina and Chile) to the arctic breeding grounds in Canada. Three waves, each containing 5000-12,000 Knots, moved throughthe area. On the restinga they fed on banks of the small mussel Brachidontes rodriguezi, virtually the only prey taken.Variably sized( 1-28 mm) Brachidontes of which those between 5 and 20 mm were eaten (8-12 mm long mussels being positively selected), occurred in high biomass densities( 23-117 g ash-free dry mass [AFDM]/m2). Due to its abundance, visibility,ease of detachment, slender shell form, and relatively weak shell, Brachidontes appear very suitable prey for Red Knots. Red Knots produced about 0.42 droppings/min. On the basis of a biomass equivalent of the droppings of approximately 62 mg AFDM, for conditions of balance (shell mass in = shell mass out) the intake rate was estimated at 0.433 mg AFDM/s. Making a few more assumptions, this translated in to a net intake rate of 2.81 W, which would allow for a fat deposition rate of less than a gram of fat per day. Using more optimistic estimates o f the various parameters in the energy budget model, a fat deposition rate of 5 g could be achieved. This is the order of magnitude predicted for Red Knots staging at San Antonio Oeste for 6-8 d and refuelling for the 1700 km long flight to the next known major staging area in southern Brazil.

Large numbers of waders migrating northward in spring use the Sivash, a large system of shallow, brackish and hypersaline lagoons in the Black Sea and Azov Sea region (Ukraine). The bottoms of these lagoons are often uncovered by the wind. Hence, for waders the time and space available for feeding depend on wind conditions. In hypersaline lagoons the benthic and pelagic fauna was very poor, consisting mainly of chironomid larvae (0.19 g AFDMom "2) and brine shrimps Artemia salina, respectively. Brine shrimp abundance was correlated with salinity, wind force, wind direction and water depth. Dunlin Calidris alpina and curlew sandpiper Calidris ferruginea were the only species feeding on brine shrimp. As brine shrimp densities are higher in deeper water, smaller waders such as broad-billed sandpipers Limicola falcinellus are too short-legged to reach exploitable densities of brine shrimp. In brackish lagoons the benthic and pelagic fauna was rich, consisting of polychaetes, bivalves, gastropods, chironomid larvae, isopods and amphipods (8.9 to 30.5 g AFDM-m'2), but there were no brine shrimps. Prey biomass increased with the distance from the coast, being highest on the site that was most frequently inundated. Dunlin, broad-billed sandpiper and grey plover Pluvialis squatarola were the most abundant birds in the brackish lagoon. Due to the effects of wind-tides only a small area was usually available as a feeding site. Gammarus insensibilis was the alternative prey resource in the water layer, and their density varied with wind direction in the same way as brine shrimp. Curlew sandpipers and dunlins in the hypersaline lagoons and broad-billed sandpipers in the brackish lagoons often changed feeding sites, probably following the variation in prey availability. Only because of the large size and variety of lagoons are waders in the Sivash always able to find good feeding sites.

In May 1990, more than 4500 km away from, and up to three weeks before arriving on their high Arctic breeding grounds, individuals of two subspecies of Knots, Calidris canutus islandica and canutus, showed ground display and song whilst foraging in flocks on the tidal flats in the Wadden Sea of Schleswig-Holstein, FRG. Similar displays and songs were recorded in May 1987 and 1988 on the staging areas of C.c. islandica in northwest Iceland. The display behaviour, identified as the 'tail-up display', is probably performed only by males towards females, and occurs commonly just after arrival at the tundra breeding sites. Tail-up displays may result in copulations both on the staging and on the breeding sites. On the staging sites, tail-up displays were most frequent in the days prior to the departure of flocks to a subsequent stopover area (Iceland) or for presumed direct flights to the Canadian and the Siberian Arctic. Our observations suggest that the behavioural condition required for reproduction may, at least in males, develop some weeks before the actual arrival in the breeding areas.

Wader species migrating through the Sivash (Ukraine) use hypersaline and brackish lagoons. We studied the use of the two habitat types, and focused on the profitability of Brine Shrimp Artemia salina, prey species in hypersaline lagoons for Dunlins Calidris alpina, Curlew Sandpipers Calidris ferruginea and Broad-billed Sandpipers Limicola falcinellus (although the latter was abundant in the brackish habitat only). Colour-marked Dunlins restricted feeding to the lagoon type in which they were initially captured.Dunlins and Curlew Sandpipers fed in areas where Brine Shrimps were of average size (0.23-0.34 mg AFDM). Artemia intake may be restricted by the visual foraging mode, as during rain and twilight pecking rates decreased to 45.9-76.8% of values measured during dry periods in full daylight. Feeding activities were higher in hypersaline than in brackish lagoon (84.6 and 69.0%, respectively). Broad-billed Sandpipers feeding on Artemia had longer handling times (0.87 s prey-1) than Dunlins and Curlew Sandpipers (0.58 and 0.54 s prey-1), which performed surface tension transport (STT) of prey in their pointed, thin bills. There were no differences in body mass increases in Dunlins in hypersaline and brackish lagoons. In
Broad-billed Sandpipers, catching results suggest an increase in body mass in the brackish lagoon only. Supported by intake rate-based calculations of potential mass gain rates, we conclude that Brine Shrimp can form a profitable prey for Dunlins and for Curlew Sandpipers, but apparently not for Broad-billed Sandpipers.

We studied phenology, staging time and refuelling in Broad-billed Sandpipers Limicola falcinellus stopping over during spring migration in the Sivash (Black Sea, Ukraine) in May 1991–94. In the study area, peak staging numbers of 2000–2500 individuals occurred in the third week of May. In May 1993, 460 birds were marked with a yellow dye and 126 of these were colour-ringed. Before 28 May no departure of birds dyed yellow could be detected; by 3 June all birds had departed. Colour-ringed adults in mid May 1993 staged for a minimum of 8.2 days. After the observed departure of large flocks (24 May and later) the staging time of colour-ringed birds decreased significantly with body mass at the time of capture. Of birds mist-netted in 1991–94, 99.3% were in full summer plumage and 89% were adults. In second-year birds, fuel deposition rate (measured between individuals) was 0.44 g/day. In adults caught from early May to 24 May, overall fuel deposition rate was 1.04 g/day (3.4% of lean body mass). Mean adult body mass in early May was 34.8 g, increasing to 45.5 g after 24 May. Estimated body mass at departure was 51 g. Departure body mass and flight range estimates suggest that although birds refuelled quickly, fuel loads are only just sufficient for an unbroken flight to Scandinavia and the Kola Peninsula. We suggest that Broad-billed Sandpipers use the Sivash as a crucial final take-off stopover site, and that they follow a ‘jumping’ migration strategy, performed under narrow time constraints.

In spring, the Ruff Philomachus pugnax passes through European inland sites in large numbers. Birds from eastern and western parts of the breeding range may differ in biometrics, but data on this species in eastern Europe are scarce. The aim of this study was to describe the biometrics of Ruffs migrating through southern Belarus in spring. In 2004, 242 birds were sexed by DNA analysis. Three birds sexed as males had female plumage but wing lengths intermediate between females and breeding-plumage males, and were identified as cryptic males or ‘faeders’. Between 2001 and 2005, 2,237 Ruffs were ringed at the study site (1,310 males in breeding plumage, 911 females and 14 faeders). There was a strong seasonal variation in sex ratio. For adult Ruffs wing length was the best predictor of sex. Total head length and tarsusplus-toe length distributions overlapped slightly between the sexes. There was evidence for slight bimodality in the distributions of wing, bill and tarsus-plus-toe length in non-faeder males and in wing and bill length distributions for females. Mean wing lengths of Ruffs passing through the Belarus study site were similar to those birds from other locations in Europe and North Africa, but different from birds from South Africa, Yamal and the middle Lena River, suggesting that Ruffs have at least two different breeding populations.

We isolated and tested 16 microsatellite loci in black-tailed godwits from the Netherlands (Limosa limosa limosa), and from Australasia (subspecies melanuroides). One locus was
monomorphic, two loci had null-alleles and one was significantly heterozygote deficient. The remaining 12 polymorphic loci had on average 7.9 alleles (range 5–11) and the mean expected heterozygosity was 0.69. No significant linkage disequilibrium between the loci was observed and all loci were autosomal. Fourteen loci were successfully cross-amplified in bar-tailed godwit (Limosa lapponica).

Seasonal bird migration involves long flights, but most time is actually spent at intermediate staging areas. The duration of stay at these sites can be evaluated with mark–recapture methods that employ day-to-day local encounters of individually marked birds. Estimates of staging duration are based on two probabilities: the immigration probability, the complement of a bird’s seniority to an area, and the emigration probability, the complement of the staying probability. Estimating total staging duration from seniority and staying probabilities requires validation for resighting data and here we compare three data categories of Ruffs Philomachus pugnax passing through The Netherlands during northward migration: (1) newly colour-ringed, (2) previously colour-ringed and (3) radio-tagged Ruffs (recorded by automated receiving stations). Between 2004 and 2008, 4363 resighting histories and 95 telemetry recording histories were collected. As sample sizes for females were low, only data for males were analysed. Possible catching effects affecting estimates of staging duration were explored. Staying probability was estimated for all data. Seniority however, could not be estimated for newly marked Ruffs; the assumption of equal ‘capture’ probability for reverse-time models applied to estimate seniority is violated for seasonal resighting histories starting with a catching event. Therefore, estimates of total staging duration were based on resightings of previously colourmarked birds only. For radio-tagged birds a minimal staging duration (time between tagging and last recording) was calculated. Modelling indicated that newly colour-ringed birds had a higher staying probability than previously colour-ringed birds, but the difference translated to a prolonged staging duration in newly ringed birds of only 0.4–0.5 d, suggesting a very small catching effect. The minimal staging duration of radio-tagged birds validated estimates of staging duration for colour-ringed birds in 2007 but not in 2005. In 2005 a low resighting probability resulted in underestimates of staging duration. We conclude that (1) estimates of staying probability can be affected by catching although effects on staging duration might be small, and that (2) low resighting probabilities can lead to underestimates in staging duration. In our study previously ringed Ruffs resighted in 2006–08 yielded reliable estimates of staging duration as data had sufficiently high resighting probabilities. Average staging durations varied between 19 d in 2008 and 23 d in 2006.

Although the mitochondrial genome in birds has highly conserved features, with protein genes similar to mammals and amphibians, several variations in gene order around the hypervariable control region have been found. Here we report a novel gene arrangement around the control region in shorebirds (Charadriiformes). In ruffs Philomachus pugnax, the mitochondrial genome between cytochrome b and 12SrRNA was over 1.5 kb longer than reported for other Charadriiformes and contained a duplication of the control region together with NADH dehydrogenase subunit 6 (ND6) and the adjacent transfer RNAs: tRNA(Pro) and tRNA(Glu). Sequence data from 68 individuals from several stopover and breeding populations show that the duplication is widespread in ruffs. Similar gene re-arrangements have been found independently in unrelated tube-nosed seabirds and spoonbills.

Aim: Over the last two decades, thousands of northward migrating ruffs (Philomachus pugnax) have disappeared from western European staging sites. These migratory ruffs were partly temperate breeding birds, but most individuals head towards the Eurasian Arctic tundras where 95% of the global population breeds. This regional decline may represent either: (1) local loss of breeding birds in western Europe, (2) a global decline, (3) shift(s) in distribution or (4) a combination of these.

Location: Northern Eurasia.

Methods: To put the declines in western Europe in context, we analysed Arctic monitoring data from the last two decades (Soloviev & Tomkovich, 2009) to detect changes in regional breeding densities across northern Eurasia. We used a novel approach applying generalized additive modelling (GAM) and generalized estimations equations (GEE).

Results: We show that the global breeding population of ruffs has made a significant eastwards shift into the Asian part of the breeding range. In the European Arctic, ruffs decreased during the last 18 years. At the same time, in western Siberia, ruffs increased. In eastern Siberia, no significant population changes could be detected. These changes corroborate the finding that during northward migration, growing numbers of ruffs avoided staging areas in the Netherlands and Sweden and started migrating along a more easterly route leading into western Siberia.

Main conclusions: We detected an unprecedented large-scale population redistribution of ruffs and suggest that this is a response to loss of habitat quality at the traditional staging site in the Netherlands.

Capsule: Fæders (males that are female look-alikes) associate with males rather than females, at several different spatial scales.

Aims: To test the prediction that the occurrence in space and time of fæders on ecological grounds should track that of females.

Methods: The fraction of fæders was estimated in five morphometric data sets that were collected over four decades in four different countries in three different seasons (comprising 9133 Ruffs). The regression of fæder–female fractions was tested against the null model assuming that the number of fæders is 1.0% of females.

Results: The fraction of fæders in catches averaged 1.03%, varying between 0.3% in autumn in the UK up to 0.85% in Sénégal in winter and 1.04% in The Netherlands in spring. On a stopover in The Netherlands the fraction decreased from 1.3% to 0.7% when the females started to arrive. At all four spatial and temporal scales the regression of fæder–female fractions deviated from the null model: we found high fractions of fæders in catches with low fractions of females, indicating that fæders rather associate with the larger-sized ´normal´ males.

Conclusion: We suggest that fæders spend the winter, and migrate with, the larger-sized lekking males, and we propose that any survival costs associated with the use of suboptimal habitats is compensated by higher reproductive success as sneakers on leks.

With 40% of the European Black-tailed Godwit population breeding in The Netherlands, this country harbours nternationally significant numbers of this species.However, ongoing agricultural intensification has resulted in the fragmentation of the population and drastic population declines since 1967. By establishing genetic diversity, genetic differentiation and gene flow on the basis of 12 microsatellites, we investigated whether the oopulation genetic structure of the Dutch Black-tailed Godwit bears the marks of these changes. Genetic diversity appeared to be moderate, and Bayesian model-based analysis of individual genotypes revealed no clustering in the Dutch populations. This was supported by pairwise FST values and AMOVA, which indicated no differentiation among the nine breeding areas. Gene flow estimates were larger than ‘‘one migrant per generation’’ between sample locations, and no isolation by distance was demonstrated. Our results indicate the maintenance of moderate levels of genetic diversity and genetic connectivity between breeding sites throughout the Dutch Black-tailed Godwit breeding population. We suggest that the Dutch Black-tailed Godwit breeding areas should be managed as a single panmictic unit, much as it is presently done.

Knowledge of stopover timing in migratory birds allows us to understand (1) a species’ migrating strategy and (2) the population dynamics at a particular stopover site along the flyway. The Ruff is an inland migratory shorebird, well studied for its reproductive behaviour but its migration is poorly known. We monitored turnover and population size during stopover in The Netherlands, by colour-marking and radio-tagging Ruffs individually. Using capture-recapture analysis, we estimated day to day survival, staging duration, staging numbers and new arrivals throughout the season. Our estimates revealed patterns not visible in normal census data.

In spring, large numbers of migrating Broad-billed Sandpipers make a stop-over in the Sivash, a shallow lagoon system in the Crimea, Ukraine, between the Black Sea and the Sea of Azov. Observed fuelling rates are high and, in just a few weeks, the birds can build up sufficient departure mass to reach their breeding grounds in a single non-stop flight (Verkuil et al. 2006). For feeding, Broad-billed Sandpipers prefer the brackish lagoons with a diverse benthic prey community. They ignore the hypersaline lagoons which are teeming with brine shrimp (Artemia sp.), a common prey for migrating Dunlins and Curlew Sandpipers in this area (Verkuil et al. 2003). In this paper we report on diet choice in relation to gut processing efficiency of different possible prey species for Broad-billed Sandpipers. We ask two questions: “Why do Broad-billed Sandpipers avoid feeding on brine shrimp in the hypersaline lagoons?” and “Do they specialize on one particular prey species in the brackish lagoons?”. Digestion efficiency of birds fed with brine shrimp was lower than for birds fed with the polychaete Nereis diversicolor or the crustacean Gammarus insensibilis. In the brackish lagoons, prey items seen ingested were both polychaetes (Nereis diversicolor) and larger crustaceans. Field observations on defecation intervals compared with identical observations on captive individuals suggest that both polychaetes and crustaceans were included in the diet. Although studies from other staging and wintering sites report that Broad-billed Sandpiper usually eat polychaetes, we suggest that they optimize their energy intake by eating a multi-course meal.

Do Reeves make different choices? Meadow selection by spring staging Ruffs Philomachus pugnax in Southwest Friesland

Each spring Ruffs stop over in large numbers in the northern part of the Netherlands, especially in Southwest Friesland. While staging, Ruffs use meadows for feeding and refuelling. A general believe is that they are attracted by the typical Dutch wet peat grasslands, with a diverse vegetation situated in an open landscape. We wanted to test this idea and to explore whether the assumed different flyways of the sexes could be related to sexual dimorphism, e.g. whether the smaller, shorter-billed females use other habitats than the males. This paper describes which meadow characteristics are correlated with meadow use and how meadow use differs between ruffs and reeves. In April and May 2003, 125 meadows in Southwest Friesland were monitored for five weeks. The total number of Ruffs decreased over the season, which is consistent with published region-wide counts. Relatively few females passed through: only in late April, when total numbers were low, the proportion females exceeded 10%. To find correlations with meadow use, 13 scored meadow characteristics were used in a multiple logistic regression model. Grass height and distance to the nearest roost proved most important (included in the model in four weeks): used meadows were closer to a roost and had shorter vegetation than unused meadows. Vegetation type, soil type, drainage level, openness of landscape and fertilisation freshness correlated with meadow use in two or three weeks. Percent flooding, fertilisation method, presence of grazers, vegetation evenness, relief and meadow size were never included in the model. The expected reference for peat meadows was not found: sand and clay soils were used more. As expected, ‘wet’ meadows and meadows in an open landscape were used more often than heavily drained meadows or meadows near buildings or trees from where predators may launch surprise attacks. Grass monocultures were least used, but the most used vegetation type was not rich but intermediately diverse in herbs. Females seem to be more extreme in meadow choice than males: groups with females used meadows that were drained less deep (thus wetter) and situated closer to the nearest roost than meadows with male-only groups. Groups with females were also more common in peat grasslands. We found indications that the sex-related differences in meadow use may be related to differences in feeding behaviour. Females foraged with higher pacing speeds. more females than males ate insects, but females had lower intake rates. Also when eating buried prey like earthworms and leatherjackets, intake rates in females were lower, although probing rates were equal. Females likely use other flyways: the proportion of females passing through this Dutch stopover site was very low compared with an important eastern European stopover site in Ukraine. At this point we can not yet decide whether this results from a difference in habitat preference induced by the size difference between the sexes or whether competition forces the females out of preferred, rich feeding sites.

Ruffs are migrant shorebirds of inland habitats. This thesis describes seasonal migration and changes in range occupation of ruffs, and presents a comparative analysis of the population genetics of ruffs and related shorebird species. Two hypotheses about shorebird evolution are addressed. Firstly, it is questioned whether instead of evolutionary constraints on migration routes (inflexible migration hypothesis), flexible routing might better explain observations on migration in shorebirds. Secondly, we test whether genetic variation in ruff and other inland, freshwater shorebirds is higher than in marine, coastal shorebirds (habitat dichotomy hypothesis).

During May 1992 the spring migration of the Broad-billed Sandpiper in the Sivash, Ukraine, was studied. The numbers increased rapidly from some tens early May up to an estimated 6,000 in the last ten days of May. The birds preferred mudflats in the eastern part of the area which proved to be rich in benthic fauna. In the central Sivash, lower numbers were found and only pelagic prey was available. The Sivash can be considered as one of the most important stop-over sites for the Broad-billed Sandpiper during spring migration, for at least 30% of the European population was found to be present.

Martin & Hockey (1993) recently suggested a 'new' method to study the diet of waders: stomach-flushing. In this note the reliability of data collected by stomach content analysis is compared with dropping analysis. For several reasons, dropping analysis has fewer disadvantages than stomach analysis in the collection of sound data on diets. Firstly, since waders can process their food very rapidly and since they generally are caught on high tide roosts, e.g. some time after feeding, most food may have passed through the stomach before the birds are stomach-pumped. Different food types are processed at different rates, so small prey and soft prey will be underestimated in stomach content samples. Further, only data on nocturnal diets are collected when birds are mist-netted during the night. Moreover, as the 'unlimited' availability of faeces and regurgitates makes more extensive analyses possible, dropping analysis can yield extra information on the ecology of waders, such as quantitative data on energy intake, prey size selection and prey choice.

The fuelling performance of long-distance migrants at staging areas indicates local conditions and determines the viability of migration routes. Here we present a first case study where long-term fuelling performance was documented along two migration routes with differential population trends. Ruffs (Philomachus pugnax) are shorebirds of inland freshwater wetlands that migrate from the sub-Saharan wintering grounds, via Europe, to the northern Eurasian breeding grounds. Assessments from 2001 to 2008 of fuelling during northward migration at the major western and eastern staging site revealed that daily mass gain rates steeply declined across years in the grasslands for dairy production in Friesland, The Netherlands, and remained constant in the Pripyat floodplains in Belarus, 1500 km further east. Migrants in Friesland decreased from 2001 to 2010 by 66%, amounting to a loss of 21,000 individuals when counts were adjusted for length of stay as determined by resightings. In the same period numbers in Pripyat increased by 12,000. Ruffs individually ringed in Friesland were resighted in subsequent springs at increasingly eastern sites including Pripyat. Our results corroborate published evidence for an eastward redistribution of Arctic breeding ruffs and suggest that the decreasing fuelling rates in the westernmost staging area contribute to this redistribution. The shift implies that responses occur within a single generation. The hypothesis that the choice of route during northward migration may be driven by food availability can now be tested by creating greater areas of wet grasslands in Friesland. When local staging conditions improve we predict that ruffs will make the reverse shift.