Willow Warbler Phylloscopus Trochilus Research Articles

Are migrant passerines faithful to their individual paths and migration timing throughout their lives?

Some publications report that passerine birds, compared with geese and waders, show much less annual faithfulness to migration routes and stopover sites, and that faithfulness to them decreases with increasing length of the migration path. The analysis of numerous recaptures of ringed birds in the Curonian Spit (Eastern Baltic) led to the opposite conclusions. The calculations were carried out on thousands of recaptures obtained over 30 years (1957–1986) from two of the most numerous species, chaffinch Fringilla coelebs Linnaeus, 1758 (Fringillidae) and willow warbler Phylloscopus trochilus (Linnaeus, 1758) (Phylloscopidae). It turned out that a significant part of the migratory populations (34–41% of recaptured birds) retains the same migration path and approximately the same migration timing in other years after ringing. Assumptions about the dependence of the degree of fidelity to migration routes on their length have not been confirmed, since the fidelity indicators of willow warbler, which has a much longer route than chaffinch, were even higher than those of the chaffinch. The data on the individual life longevity of the recaptured migrants (up to 9 years in the chaffinch and up to 4 years in the willow warbler) confirm the fidelity to the same migration path throughout the life of the studied birds.

Checklist of Hippoboscidae (Diptera) from Romania

The checklist of louse flies or keds from the family Hippoboscidae in Romania with 14 species is given. Among them, six species have been newly recorded from Romania, from Natura 2000 site “Dunele Marine de la Agigea” Natural Reserve; namely: Icosta minor (Bigot in Thomson, 1858), Ornithoica turdi (Olivier in Latreille, 1812), Ornithomya chloropus Bergroth, 1901, Ornithomya fringillina Curtis, 1836, Ornithophila gestroi (Rondani, 1878), and Ornithophila metallica (Schiner, 1864). Out of the total, seven species are autochthonous, while the other seven are probably non-native species, either spreading invasively or only occasionally being imported to Romania or migrating to the country along with their hosts. Three new host-parasite associations have been reported for the first time. Specifically, the eastern olivaceous warbler Iduna pallida (Hemprich et Ehrenberg, 1833) represents new host species for I. minor and O. turdi, while the willow warbler Phylloscopus trochilus (Linnaeus, 1758) represents a new host species for O. gestroi.

Two- and three-dimensional territories and territory overlap of Willow Warblers Phylloscopus trochilus in Arctic forests

Two- and three-dimensional territories and territory overlap of Willow Warblers Phylloscopus trochilus in Arctic forests

Intra‐ and interspecific variation in trace element concentrations in feathers of north European trans‐African migrants

The knowledge of migratory connectivity is important for understanding the potential drivers of populations and it is thus important for conservation implications. Migratory connectivity of species can be studied using exogenous, such as rings and transmitters, or endogenous markers, such as stable isotopes and trace elements. The use of trace elements has been much less frequently studied compared to stable isotopes. Trace elements can be studied from the feathers of birds and this does not necessarily require trapping of individuals. Here we studied the variation of 18 different trace elements in feathers of two long‐distance trans‐African migrants, willow warblers Phylloscopus trochilus and barn swallows Hirundo rustica, using body feathers of museum specimens of birds from Finnish breeding grounds. The trace elements were measured using laser‐ablation inductively‐coupled‐plasma mass‐spectrometry (LA‐ICP‐MS). We show that trace element concentrations were relatively stable along the rachis within the same feather except in Ni and S, which showed a quadratic pattern. In general, variation within feathers of the same individuals was smaller than in feathers between individuals for most elements. Furthermore, concentrations of 11 trace elements showed significantly higher concentrations in willow warbler feathers collected in spring than in autumn, moulted in African wintering grounds and European breeding grounds, respectively. Last, concentrations of seven trace elements were significantly higher in the spring feathers of willow warblers compared to barn swallows. This suggests that trace elements could be used to separate moulting grounds of the birds on the larger scale within the same species, but also sampling design should be carefully considered.

Inversions maintain differences between migratory phenotypes of a songbird

Structural rearrangements have been shown to be important in local adaptation and speciation, but have been difficult to reliably identify and characterize in non-model species. Here we combine long reads, linked reads and optical mapping to characterize three divergent chromosome regions in the willow warbler Phylloscopus trochilus, of which two are associated with differences in migration and one with an environmental gradient. We show that there are inversions (0.4–13 Mb) in each of the regions and that the divergence times between inverted and non-inverted haplotypes are similar across the regions (~1.2 Myrs), which is compatible with a scenario where inversions arose in either of two allopatric populations that subsequently hybridized. The improved genomes allow us to detect additional functional differences in the divergent regions, providing candidate genes for migration and adaptations to environmental gradients.

Migration direction in a songbird explained by two loci

Migratory routes and remote wintering quarters in birds are often species and even population specific. It has been known for decades that songbirds mainly migrate solitarily, and that the migration direction is genetically controlled. Yet, the underlying genetic mechanisms remain unknown. To investigate the genetic basis of migration direction, we track genotyped willow warblers Phylloscopus trochilus from a migratory divide in Sweden, where South-West migrating, and South-East migrating subspecies form a hybrid swarm. We find evidence that migration direction follows a dominant inheritance pattern with epistatic interaction between two loci explaining 74% of variation. Consequently, most hybrids migrate similarly to one of the parental subspecies, and therefore do not suffer from the cost of following an inferior, intermediate route. This has significant implications for understanding the selection processes that maintain narrow migratory divides.

Autumn fueling behavior in passerines in relation to migratory distance and daylength.

Songbirds have evolved diverse strategies to cope with seasonality, including long-, medium-, and short-distance migration. There is some evidence that birds with a longer migration distance deposit fuel faster. However, most studies focus on long-distance migrants. Comparisons between species with different migration distances are necessary to broaden our understanding of fueling capacity in migratory birds. We present maximum fuel deposition rates of five songbird species migrating along the southeast coast of Sweden in autumn with migration distances ranging from long (neotropical migrant) to short (partial/irruptive migrant) (Willow Warbler Phylloscopus trochilus, Lesser Whitethroat Curruca curruca, Common Chiffchaff P.collybita, European Robin Erithacus rubecula, and Blue Tit Cyanistes caeruleus). The birds were fed ad libitum in captivity and were exposed to either extended or natural daylength. All species ceased to increase in mass when they reached a certain fuel load, generally corresponding to migration distance, despite unlimited access to food and ample time for foraging. Blue Tits, Willow Warblers, and Lesser Whitethroats had the highest fuel deposition rates with extended daylength (19%, 20%, and 20%, respectively), and about 13% with natural daylength, which is comparable to the highest rates found in migratory songbirds in nature. European Robins and Common Chiffchaffs that winter in the temperate Mediterranean had the lowest fuel deposition rates (12% and 12% with extended daylength, respectively). Our results suggest that the long- and short-distance migrants in this study have developed an extreme capacity for rapid refueling for different reasons; speedy migration to distant wintering grounds or winter survival in Scandinavia. This study contributes to our current knowledge of maximum fuel deposition rates in different species and the limitations posed by daylength. We highlight the need for future studies of species with different migration strategies in order to draw broad conclusions about fueling strategies of migratory birds.

Breeding ground temperature rises, more than habitat change, are associated with spatially variable population trends in two species of migratory bird

Habitat loss and climate change are key drivers of global biodiversity declines but their relative importance has rarely been examined. We attempted to attribute spatially divergent population trends of two Afro‐Palaearctic migrant warbler species, Willow Warbler Phylloscopus trochilus and Common Chiffchaff Phylloscopus collybita, to changes in breeding grounds climate or habitat. We used bird counts from over 4000 sites across the UK between 1994 and 2017, monitored as part of the BTO/JNCC/RSPB Breeding Bird Survey. We modelled Willow Warbler and Common Chiffchaff population size and growth in relation to habitat, climate and weather. We then used the abundance model coefficients and observed environmental changes to determine the extent to which spatially varying population trends in England and Scotland were consistent with attribution to climate and habitat changes. Both species' population size and growth correlated with habitat, climate and weather on their breeding grounds. Changes in habitat, in particular woodland expansion, could be linked to small population increases for both species in England and Scotland. Both species' populations correlated more strongly with climate than weather, and both had an optimum breeding season temperature: 11°C for Willow Warbler and around 13.5°C for Common Chiffchaff (with marginally different predictions from population size and growth models). Breeding ground temperature increases, therefore, had the potential to have caused some of the observed Willow Warbler declines in England (where the mean breeding season temperature was 12.7°C) and increases in Scotland (mean breeding season temperature was 10.2°C), and some of the differential rates of increase for Common Chiffchaff. However, much of the variation in species' population abundance and trends were not well predicted by our models and could be due to other factors, such as species interactions, habitat and climate change in their wintering grounds and on migration. This study provides evidence that the effect of climate change on a species may vary spatially and may switch from being beneficial to being detrimental if a temperature threshold is exceeded.

An examination of perched Willow Warblers Phylloscopus trochilus singing on one leg

Territory-holding male Willow Warblers Phylloscopus trochilus stood on one leg when they were singing at song posts for extended periods of time. The other leg was tucked in the breast plumage and not visible. The length of time spent on a twig was positively correlated to the use of unipedal stance. Observed birds spent longer pose time perched on one leg than on two legs. The right leg and the left leg were used at similar frequencies. The reason for this behaviour might be to save energy, by reducing heat loss through the skin of the tucked leg.

Climate in Africa sequentially shapes spring passage of Willow Warbler Phylloscopus trochilus across the Baltic coast.

BackgroundMany migrant birds have been returning to Europe earlier in spring since the 1980s. This has been attributed mostly to an earlier onset of spring in Europe, but we found the timing of Willow Warblers’ passage to be influenced by climate indices for Africa as much as those for Europe. Willow Warblers’ spring passage through northern Europe involves populations from different wintering quarters in Africa. We therefore expected that migration timing in the early, middle and late periods of spring would be influenced sequentially by climate indices operating in different parts of the winter range.MethodsUsing data from daily mistnetting in 1 April–15 May over 1982–2017 at Bukowo (Poland, Baltic Sea coast), we derived an Annual Anomaly (AA, in days) of Willow Warbler spring migration. We decomposed this anomaly into three main periods (1–26 April, 27 April–5 May, 6–15 May); one-third of migrants in each period. We modelled three sequential time series of spring passage using calendar year and 15 large-scale climate indices averaged over the months of Willow Warblers’ life stages in the year preceding spring migration as explanatory variables in multiple regression models. Nine climate variables were selected in the best models. We used these nine explanatory variables and calculated their partial correlations in models for nine overlapping sub-periods of AA. The pattern of relationships between AA in these nine sub-periods of spring and the nine climate variables indicated how spring passage had responded to the climate. We recommend this method for the study of birds’ phenological responses to climate change.ResultsThe Southern Oscillation Index and Indian Ocean Dipole in Aug–Oct showed large partial correlations early in the passage, then faded in importance. For the Sahel Precipitation Index (PSAH) and Sahel Temperature Anomaly (TSAH) in Aug–Oct partial correlations occurred early then peaked in mid-passage; for PSAH (Nov–March) correlations peaked at the end of passage. NAO and local temperatures (April–May) showed low correlations till late April, which then increased. For the Scandinavian Index (Jun–Jul) partial correlations peaked in mid-passage. Year was not selected in any of the best models, indicating that the climate variables alone accounted for Willow Warblers’ multiyear trend towards an earlier spring passage.DiscussionClimate indices for southern and eastern Africa dominated relationships in early spring, but western African indices dominated in mid- and late spring. We thus concluded that Willow Warblers wintering in southern and eastern Africa dominated early arrivals, but those from western Africa dominated later. We suggest that drivers of phenological shifts in avian migration are related to changes in climate at remote wintering grounds and at stopovers, operating with climate change in the north, especially for species with complex and long-distance migration patterns.

Seasonality and social factors, but not noise pollution, influence the song characteristics of two leaf warbler species.

Changes in the acoustic signalling of animals occupying urban ecosystems is often associated with the masking effects of noise pollution, but the way in which they respond to noise pollution is not straightforward. An increasing number of studies indicate that responses can be case specific, and some species have been found to respond differently to high levels of natural versus anthropogenic noise, as well as different levels of the latter. While the perception of noise between species may vary with its source, amplitude and temporal features, some species may possess broader environmental tolerance to noise pollution, as they use higher frequency vocalizations that are less masked by low-frequency urban noise. In this study, we explored the song variation of two closely related leaf warblers, the Common Chiffchaff Phylloscopus collybita and the Willow Warbler Phylloscopus trochilus, inhabiting urban green spaces and nonurban forests. The main goal of our study was to evaluate the impact of moderate levels of noise pollution on the songs of species which use higher frequency vocalizations and large frequency bandwidth. Previous studies found that the Common Chiffchaff modified their song in response to intense noise pollution, while no such data is available for the Willow Warbler. However, the majority of urban green spaces, which serve as wildlife hot spots in urban environments are usually polluted with moderate noise levels, which may not mask the acoustic signals of species that communicate with higher frequency. We analysed the spectral and temporal song parameters of both warblers and described the ambient noise present in males’ territories. Additionally, we looked at the social and seasonal aspects of bird song, since there is more than just noise in urban ecosystems which may affect acoustic communication. We found no evidence for noise-related bird song divergence in either species, however, we showed that social factors, time of day and season influence certain Common Chiffchaff and Willow Warbler song characteristics. Lack of noise-related bird song divergence may be due to the relatively low variation in its amplitude or other noise features present within the song frequency range of the studied species. Similar results have previously been shown for a few songbird species inhabiting urban ecosystems. Although in many cases such results remain in the shadow of the positive ones, they all contribute to a better understanding of animal communication in urban ecosystems.

Consequences of spring arrival dates for the breeding phenology of migratory warblers

ABSTRACT Capsule Early male arrival on the breeding grounds results in early pairing but not early nesting in Chiffchaffs Phylloscopus collybita, and Chiffchaffs can nest, fail, and re-nest before Willow Warblers Phylloscopus trochilus begin nesting. Aims To quantify the consequences of timing of arrival for the subsequent timing of pairing, nesting, and re-nesting of short-distance (Chiffchaff) and long-distance (Willow Warbler) migrants. Methods The arrival dates of 118 Chiffchaffs and 20 Willow Warblers were measured from March to June over 10 weeks in Foxley Wood nature reserve, Norfolk. Colour-ringing of 56 Chiffchaffs (55 males, 1 female) and 11 Willow Warblers (10 males, 1 female) was used to relate individual arrival dates to timing of male pairing, clutch initiation, and re-nesting. Results Male Chiffchaffs started to arrive in early March and increased rapidly in number until early April, while the arrival of male Willow Warblers began in early April. Early-arriving male Chiffchaffs paired earlier than later-arriving individuals, but timing of clutch initiation was unrelated to male arrival dates. Early nesting by Chiffchaffs allowed replacement clutches following nest loss, the earliest of which occurred 12 days after the first Willow Warbler male had paired. Conclusions Although early arrival in male Chiffchaffs does not translate into earlier nesting, timing of nesting in Chiffchaffs was sufficiently early to allow time for replacement clutches following nest loss. The later arrival of Willow Warblers is likely to mean fewer opportunities for replacement clutches following nest loss. This difference in breeding phenology could therefore contribute to differences in productivity between the species, especially if nest failure rates are high.

Nest Site Selection and Nest Construction in the Willow Warbler (Phylloscopus trochilus L., 1758) (Sylviidae, Aves) in the Taiga Zone of Northwestern Russia

Nest Site Selection and Nest Construction in the Willow Warbler (Phylloscopus trochilus L., 1758) (Sylviidae, Aves) in the Taiga Zone of Northwestern Russia

Autumn migration direction of juvenile willow warblers (Phylloscopus t. trochilus and P. t. acredula) and their hybrids assessed by qPCR SNP genotyping

BackgroundsGeographic regions, where two closely related taxa with different migration routes come into contact, are known as migratory divides. Hybrids originating from migratory divides are hypothesized to migrate intermediately relative to the parental populations. Few studies have tested this hypothesis in wild birds, and only in hybrids that have completed the migration back to the breeding grounds. Here, we make use of the well-established migration routes of willow warblers (Phylloscopus trochilus), for which the subspecies trochilus and acredula have migration-associated genetic markers on chromosomes 1 and 5. The genetic approach enabled us to analyze the geographic distribution of juveniles during their first autumn migration, predicting that hybrids should be more frequent in the central flyway over Italy than along the typical SW routes of trochilus and SE routes of acredula.MethodsBlood and feather samples were collected from wintering birds in Africa (n = 69), and from juveniles during autumn migration in Portugal (n = 33), Italy (n = 38) and Bulgaria (n = 32). Genotyping was carried out by qPCR SNP assays, on one SNP each on chromosome 1 (SNP 65) and chromosome 5 (SNP 285). Both these SNPs have alternative alleles that are highly fixed (> 97%) in each of the subspecies.ResultsThe observed combined genotypes of the two SNPs were associated with the known migration routes and wintering distributions of trochilus and acredula, respectively. We found hybrids (HH) among the juveniles in Italy (5/38) and in Portugal (2/33). The proportion of hybrids in Italy was significantly higher than expected from a background rate of hybrid genotypes (1.5%) in allopatric populations of the subspecies.ConclusionsOur genetic approach to assign individuals to subspecies and hybrids allowed us to investigate migration direction in juvenile birds on their first migration, which should better reflect the innate migratory direction than studies restricted to successful migrants. The excess of hybrids in Italy, suggests that they employ an intermediate route relative to the parental populations. Our qPCR SNP genotyping method is efficient for processing large sample sizes, and will therefore be useful in migration research of species with known population genetic structure.

Benefits and costs of native reforestation for breeding songbirds in temperate uplands

Global tree planting initiatives may benefit biodiversity depending on woodland type, but ecological effects must be understood when woodland replaces open habitats supporting characteristic wildlife. In the UK's temperate uplands, large-scale reforestation is replacing long-established open ‘moorland’ (heath, bog and grassland) supporting breeding bird communities of conservation importance. We quantified breeding bird species richness and abundance in 8–24 year-old native woodland plantations in Scotland and adjacent moorland and used bird densities to predict potential future abundance changes in woodland and moorland avian indicator species from recent national-level woodland creation policies. Bird species richness at point counts increased with increasing woodland cover, height and age and declined with increasing elevation. Differing abundances of bird species of conservation concern between woodland and moorland were related to their associations with vegetation measures, especially woodland cover and tree species composition. The creation of 54.9 km2 of native woodland in Scotland across 2017 and 2018 predicts reduced Meadow Pipit Anthus pratensis (moorland indicator) abundance of 6214 individuals or 0.13% of current UK population, and increased Willow Warbler Phylloscopus trochilus (indicator of young woodland) abundance of 6040 individuals or 0.13% of current UK population. Native woodland plantations comprised c34% of new woodland creation and the projections should be extended to other woodland types in particular non-native commercial conifer forestry. Native reforestation of open ground offers net gains in bird species richness but could disbenefit open-ground birds including those of conservation concern. Where retention of open-ground species is desired, landscape-scale reforestation should consider both woodland and open-ground wildlife.

Nest Site Selection and Nest Construction in the Willow Warbler (<i>Phylloscopus trochilus</i> L., 1758) (Sylviidae, Aves) in the Tajga Zone of Northwest Russia

Журнал принимает на русском и английском языках статьи, представляющие результаты научных исследований в различных областях теоретической и прикладной экологии. Приоритет отдается научным статьям, основанным на явно сформулированных гипотезах.

Winter site use by Afro-Palearctic migrants in Ghana: site persistence and densities of Willow Warbler, Pied Flycatcher, Melodious Warbler and Common Redstart

Little is known about the variation within and among species of long-distance migrants in behavioural strategies and habitat choice on their non-breeding grounds. We report results from regular ringing operations carried out during the winter seasons 2009–2013 and transect counts in 2013, 2015 and 2016 in the Sudan Savanna Zone in Ghana. The best supported capture–mark–recapture model included species-specific probabilities of stay between within-season periods but no differences in resighting probability among species or sites. This model indicated that less than one-third of the Willow Warblers Phylloscopus trochilus and half of the Melodious Warblers Hippolais polyglotta stayed at wintering sites during more than 10 d, whereas for Pied Flycatcher Ficedula hypoleuca and Common Redstart Phoenicurus phoenicurus up to 90% stayed for more than 10 d, indicating itinerant wintering behaviour in the warblers and longer non-breeding residency in Pied Flycatcher and Common Redstart. Densities varied among years, but Pied Flycatchers were consistently most numerous in well-matured woodland habitat and Willow Warblers in disturbed habitat. Recaptures among years were too low for meaningful estimates of winter site fidelity, yet recurrence was recorded in three species. We speculate that habitat use is directly related to degree of territory defence and itinerancy.

Breeding bird assemblages supported by developing upland shrub woodland are influenced by microclimate and habitat structure

ABSTRACTCapsule: Local micro-climate, as well as habitat, influences the abundance of birds within dynamically changing upland habitats.Aims: To identify the relative importance of near-ground temperature (as an index of climate at a scale typical of the territory of breeding passerines) and habitat for some breeding birds in upland Scotland where land uses and habitats are changing.Methods: Timed point counts sampled breeding birds within the marginal uplands of Scotland in habitats at successional stages between pasture and shrubland. Habitat composition and ambient temperatures were recorded at the same sampling points. Generalized linear mixed models were used to assess associations of bird abundance, species richness and species diversity with habitat and ambient near-ground temperature.Results: Species richness increased with mean temperature, was greatest within areas of shrubland and was lowest in open habitats. Different species showed individual associations with temperature and habitat. Species predominantly associated with shrubland tended to have a negative association with temperature.Conclusions: Understanding the habitat and climatic niche requirements of different species will facilitate appropriate land management to be targeted within appropriate climatic patches. For example, open habitats suitable for Whinchats Saxicola rubetra should be within warmer climate patches (typically lower elevation or southern aspects) while shrublands can support Willow Warblers Phylloscopus trochilus at cooler elevations and aspects. Management that delivers a mosaic of habitats, spanning areas of climatic heterogeneity should enhance the diversity of birds supported in the upland margins and potentially their resilience to changing environmental conditions.

Phenotypic and genetic characterization of the East Siberian Willow Warbler (Phylloscopus trochilus yakutensis Ticehurst, 1935) in relation to the European subspecies

Long-distance migrants with transcontinental breeding ranges are of particular interest for the study of local adaptation and geographic differentiation in birds. We compared phenotypes and genotypes between Far East Siberian Willow Warblers Phylloscopus trochilus yakutensis Ticehurst, 1935 with the European subspecies P. t. trochilus Linnaeus, 1758 and P. t. acredula Linnaeus, 1758. We found significant differences in mean body size and plumage colour, but intra-population variation overlapped extensively between the European and Siberian populations. We used stable isotope composition in winter-grown flight feathers as a proxy for wintering sites and found differences between all three subspecies, indicating different wintering grounds. Out of four nuclear loci analyzed (three of which are known to be substantially divergent between the European subspecies), none allowed to seperate East Siberian yakutensis from North Scandinavian acredula. Hence, neither phenotypic traits nor the currently available genetic resources provide diagnostic criteria for confidently assigning individual Willow Warblers to a particular subspecies. Despite extensive overlap in phenotypes and genotypes, we propose that the subspecies names can still be used as biogeographical references to the three Willow Warbler populations that differ in migration strategies. We propose to use yakutensis for Willow Warblers breeding east of the Ural Mountains that presumably initiate autumn migration towards the southwest or west, in contrast to the genetically most similar acredula that start autumn migration towards the southeast or south. Future field studies are needed to elucidate whether the longitudinal variation in phenotype is a cline, or whether a clear contact zone between these subspecies can be identified.

Ten grams and 13,000\xa0km on the wing \u2013 route choice in willow warblers Phylloscopus trochilus yakutensis migrating from Far East Russia to East Africa

BackgroundHigh-latitude bird migration has evolved after the last glaciation, in less than 10,000–15,000 years. Migrating songbirds rely on an endogenous migratory program, encoding timing, fueling, and routes, but it is still unknown which compass mechanism they use on migration. We used geolocators to track the migration of willow warblers (Phylloscopus trochilus yakutensis) from their eastern part of the range in Russia to wintering areas in sub-Saharan Africa. Our aim was to investigate if the autumn migration route can be explained by a simple compass mechanism, based on celestial or geomagnetic information, or whether migration is undertaken as a sequence of differential migratory paths possibly involving a map sense. We compared the recorded migratory routes for our tracked birds with simulated routes obtained from different compass mechanisms.ResultsThe three tracked males were very similar in the routes they took to their final wintering sites in southern Tanzania or northern Mozambique, in their use of stopover sites and in the overall timing of migration. None of the tested compass mechanisms could explain the birds’ routes to the first stopover area in southwest Asia or to the destination in Southeast Africa without modifications. Our compass mechanism simulations suggest that the simplest scenarios congruent with the observed routes are based on either an inclination or a sun compass, assuming two sequential steps.ConclusionsThe birds may follow a magnetoclinic route coinciding closely with the tracks by first moving west, i.e. closer to the goal, and thereafter follow a constant apparent angle of inclination to the stopover site. An alternative would be to use the sun compass, but with time-adjustments along the initial part of the migration to the first stopover, and thereafter depart along a new course to the winter destination. A combination of the two mechanisms cannot be ruled out, but needs to be confirmed in future studies.