Do Red Knots (Calidris Canutus Islandica) routinely skip Iceland during southward migration?

Subspecies Calidris canutus islandica of the Red Knot breeds on the arctic tundra of northeastern Canada and northern Greenland and winters along the coasts of northwestern Europe. During northward migration, it stops over in either Iceland or northern Norway. It has been assumed that it does the same during southward migration. Using ratios of stable carbon isotopes (δ ¹³ C) in whole blood, blood cells, and plasma, we investigated evidence for a stopover in Iceland en route from the breeding grounds to the Dutch Wadden Sea. With the expected diet (shellfish) and stopover duration at Iceland (12-15 days, maximum 17 days) and the turnover rates of blood cells (15.1 days) and plasma (6.0 days), Red Knots that stopped in Iceland should arrive with a blood (cell) δ ¹³ C midway between a tundra (-24.7[per thousand]) and a marine value (-14.0[per thousand]) and a plasma δ¹³ C approaching the marine value (-15.3[per thousand]). However, many adults arriving at the Wadden Sea had δ¹³ C ratios in blood (cells) and plasma below these levels, and some arrived with clear tundra signals in blood cells, suggesting that they skipped Iceland during southward migration. Surprisingly, available data suggest this also to be true for juveniles during their first southward migration. The δ ¹³ C signature of second-year birds confirmed that they oversummered in the Wadden Sea. Our findings contradict the largely untested idea that juvenile shorebirds make more stopovers than adults as well as the idea that the migration between the Nearctic and Europe is necessarily a two-leg process.

What decision rules might pink-footed geese use to depart on migration? An individual-based model

Decisions taken during migration can have a large effect on the fitness of birds. Migration must be accurately timed with food availability to allow efficient fueling but is also constrained by the optimal arrival date at the breeding site. The decision of when to leave a site can be driven by energetics (sufficient body stores to fuel flight), time-related cues (internal clock under photoperiodic control), or external cues (temperature, food resources). An individual based model (IBM) that allows a mechanistic description of a range of departure decision rules was applied to the spring migration of pink-footed geese (Anser brachyrhynchus) from wintering grounds in Denmark to breeding grounds on Svalbard via 2 Norwegian staging sites. By comparing predicted with observed departure dates, we tested 7 decision rules. The most accurate predictions were obtained from a decision rule based on a combination of cues including the amount of body stores, date, and plant phenology. Decision rules changed over the course of migration with the external cue decreasing in importance and the time-related cue increasing in importance for sites closer to breeding grounds. These results are in accordance with descriptions of goose migration, following the “green-wave”: Geese track the onset of plant growth as it moves northward in spring, with an uncoupling toward the end of the migration if time is running out. We demonstrate the potential of IBMs to study the possible mechanisms underlying stopover ecology in migratory birds and to serve as tools to predict consequences of environmental change.

Animal migration : linking models and data beyond taxonomic limits

An international workshop on animal migration was held at the Lorentz Center in Leiden, The Netherlands, 2–6 March 2009, bringing together leading theoreticians and empiricists from the major migratory taxa, aiming at the identification of cutting-edge questions in migration research that cross taxonomic borders.

The consequences of climate-driven stop-over sites changes on migration schedules and fitness of Arctic geese

1. How climatic changes affect migratory birds remains difficult to predict because birds use multiple sites in a highly interdependent manner. A better understanding of how conditions along the flyway affect migration and ultimately fitness is of paramount interest.

2. Therefore, we developed a stochastic dynamic model to generate spatially and temporally explicit predictions of stop-over site use. For each site, we varied energy expenditure, onset of spring, intake rate and day-to-day stochasticity independently. We parameterized the model for the migration of pink-footed goose Anser brachyrhynchus from its wintering grounds in Western Europe to its breeding grounds on Arctic Svalbard.

3. Model results suggested that the birds follow a risk-averse strategy by avoiding sites with comparatively high energy expenditure or stochasticity levels in favour of sites with highly predictable food supply and low expenditure. Furthermore, the onset of spring on the stop-over sites had the most pronounced effect on staging times while intake rates had surprisingly little effect.

4. Subsequently, using empirical data, we tested whether observed changes in the onset of spring along the flyway explain the observed changes in migration schedules of pink-footed geese from 1990 to 2004. Model predictions generally agreed well with empirically observed migration patterns, with geese leaving the wintering grounds earlier while considerably extending their staging times in Norway.

Does migration of hybrids contribute to post-zygotic isolation in flycatchers?

In the face of hybridization, species integrity can only be maintained through post-zygotic isolating barriers (PIBs). PIBs need not only be intrinsic (i.e. hybrid inviability and sterility caused by developmental incompatibilities), but also can be extrinsic due to the hybrid's intermediate phenotype falling between the parental niches. For example, in migratory species, hybrid fitness might be reduced as a result of intermediate migration pathways and reaching suboptimal wintering grounds. Here, we test this idea by comparing the juvenile to adult survival probabilities as well as the wintering grounds of pied flycatchers (Ficedula hypoleuca), collared flycatchers (Ficedula albicollis) and their hybrids using stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) in feathers developed at the wintering site. Our result supports earlier observations of largely segregated wintering grounds of the two parental species. The isotope signature of hybrids clustered with that of pied flycatchers. We argue that this pattern can explain the high annual survival of hybrid flycatchers. Hence, dominant expression of the traits of one of the parental species in hybrids may substantially reduce the ecological costs of hybridization.

Intake rates, stochasticity, or onset of spring : what aspects of food availability affect spring migration patterns in Pink-footed Geese Anser brachyrhynchus?

Long-distance bird migration consists of several flight episodes interrupted by a series of resting and refuelling periods on stopover sites. We assessed the role of food availability as the determinant of staging decisions focusing on the following three aspects of food availability: intake rates, stochasticity in intake rates and onset of spring. Using stochastic dynamic modelling, we investigated their impact on staging times and expected fitness. Subsequently, we compared relations in the use of the stopover sites as predicted by the model with empirical data of the Svalbard-breeding population of Pink-footed Goose Anser brachyrhynchus collected in the period 1990–2002. Our results indicate that, for the case of Pink-footed Geese, spring phenology determines a major part of the migration schedule. In contrast to our expectations, intake rates were generally only of minor importance; however, when approaching the breeding grounds their significance increased. Expected fitness at arrival on the breeding grounds showed that the geese can compensate for changes in a broad range of food availability and also cope with varying degrees of stochasticity. However, declining intake rates at the last stopover site or very late onsets of spring clearly decreased fitness. As predicted by the model, the use of stopover sites was interdependent – from empirical data we derived negative relationships between the staging durations of subsequent sites. These results lend credit to an integrated spatially explicit approach focussing on multiple stopover site characteristics when attempting to improve our understanding of bird migration.

Seasonal winds drive water temperature cycle and migration patterns of Southern Australian giant crab Pseudocarcinus gigas

The giant crab Pseudocarcinus gigas occurs along the continental shelf break of southern Australia. During the summer alongshore winds cause cooler water to upwell onto the shelf, and the crabs move from deeper water onto the shelf where there is more food. The combination of a preferred thermal niche and a depth-stratified food supply defines the favorable foraging environments that enhance the growth of P. gigas. Climate change is expected to cause a southerly shift of the austral subtropical high-pressure belt, and modelers have predicted more upwelling-favorable winds. The associated increase in the circulation of cooler water across the shelf is likely to provide P. gigas with an increased access to benthic food resources and their growth rate may increase in some regions.

Northward migration of Afro-Siberian Knots Calidris canutus canutus : high variability in Red Knot numbers visiting staging sites on the French Atlantic coast, 1979–2009

The Afro–Siberian Red Knot subspecies, Calidris canutus canutus, winters mainly on Banc d’Arguin, Mauritania, West Africa. An International Wader Study Group project carried out in 1979 suggested that during northward migration Red Knots cover their migration between the wintering grounds and the Siberian breeding grounds in two long-distance non-stop flights, stopping only in the Wadden Sea in Schleswig-Holstein, Germany. Each year Red Knots also visit staging sites along the French Atlantic coast in addition to the German Wadden Sea. Ever since 1979, the French staging sites have been counted on a regular basis and here we present the count data from these 30 years. In some years more than 20% of the population used the French Atlantic coast as a staging site, but numbers are highly variable from one year to the next. We suggest that high numbers in France might occur when birds have to stop short of the Wadden Sea because of head-winds and/or a lack of tail-winds en route from West Africa.

On 4 June 2008 Siberian Red Knots at Elbe Mouth kissed the canonical evening migration departure rule goodbye

Observations of departing Siberian-breeding Red Knots Calidris canutus canutus from their central staging site during northward migration, the Schleswig-Holstein Wadden Sea, Germany, in early June 2008, challenge the established notion that departing long-distance migrating waders only leave around sunset. During four days we scanned several thousand Red Knots for colour-ringed individuals and found a total of 20 different individuals that were previously ringed at either their main wintering site, the Banc d'Arguin in Mauritania, or at stopover sites on the Atlantic coast of France. Body masses of captured Red Knots in Schleswig-Holstein were higher than 200 g and hematocrite values showed an average of 58%, clearly indicating that they were ready for take-off. On all except one evening, we noted impressive departure movements during the incoming tide. On that exceptional evening a cold front thunderstorm passed over the area. Late the next morning, thousands of Red Knots departed during the incoming tide. We assume that the birds avoided taking off in adverse weather conditions and elaborate why Red Knots presumably traded off advantages from departing during twilight. We suggest that during spring migration, schedules are so tight that further delays decrease fitness, either because it would cause another full day of exposure to high predation risk by falcons, or because of conditions upon arrival on the tundra.

Migration, citizenship and intercultural relations : looking through the lens of social inclusion

Migration, Citizenship and Intercultural Relations reflects on the tensions and contradictions that arise within debates on social inclusion, arguing that both the concept of social inclusion and policy surrounding it need to incorporate visions of citizenship that value ethnic diversity. Presenting the latest empirical research from Australia and engaging with contemporary global debates on questions of identity, citizenship, intercultural relations and social inclusion, this book unsettles fixed assumptions about who is included as a valued citizen and explores the possibilities for engendering inclusive visions of citizenship in local, national and transnational spaces.