Individual variability and versatility in an eco-evolutionary model of avian migration

Seasonal migration is a complex and variable behaviour with the potential to promote reproductive isolation. In Eurasian blackcaps (Sylvia atricapilla), a migratory divide in central Europe separating populations with southwest (SW) and southeast (SE) autumn routes may facilitate isolation, and individuals using new wintering areas in Britain show divergence from Mediterranean winterers. We tracked 100 blackcaps in the wild to characterize these strategies. Blackcaps to the west and east of the divide used predominantly SW and SE directions, respectively, but close to the contact zone many individuals took intermediate (S) routes. At 14.0° E, we documented a sharp transition from SW to SE migratory directions across only 27 (10–86) km, implying a strong selection gradient across the divide. Blackcaps wintering in Britain took northwesterly migration routes from continental European breeding grounds. They originated from a surprisingly extensive area, spanning 2000 km of the breeding range. British winterers bred in sympatry with SW-bound migrants but arrived 9.8 days earlier on the breeding grounds, suggesting some potential for assortative mating by timing. Overall, our data reveal complex variation in songbird migration and suggest that selection can maintain variation in migration direction across short distances while enabling the spread of a novel strategy across a wide range

Differential migration strategies of the Wood Sandpiper (Tringa glareola) – genetic analyses reveal sex differences in morphology and spring migration phenology

Sex and age differences in spring migration phenology were studied in the Wood Sandpiper - a monomorphic wader of inland wetlands. Birds were sexed by DNA analysis. During the rapid passage through NE Poland in 2003, the first males occurred 4 days before the first females. Thereafter both sexes were represented. Median migration dates were significantly earlier for males than for females among the older age group (2+ birds). A similar tendency was shown for second-year birds (2K). The sex differences can be explained by earlier arrival of males at the breeding grounds. Second-year birds migrated significantly later than older birds. Females were significantly larger than males in total head, tarsus plus toe, wing length and body mass. Total head length allowed for identification of a low proportion of 2+ males and females, but the other measurements did not allow reliable sexing because of size range overlaps between the sexes. Principle Component Analysis (PCA), where the 'body size coefficient' (PC1) combines three linear body measurements, slightly improved the accuracy of the sexing. Thus, genetic sexing of Wood Sandpipers is preferable. We recommend application of molecular sexing in studies of the behaviour of sex, age and population groups in monomorphic species

Long-term changes in autumn migration timing of Garden Warblers Sylvia borin at the southern Baltic coast in response to spring, summer and autumn temperatures

AbstractMany migrant European birds have been departing their breeding grounds earlier in recent decades in response to rising temperatures from climate change. We examined long-term changes in the autumn migration timing of immature Garden Warblers using data from ringing station Bukowo-Kopań on the Polish Baltic coast in 1967–2018. We calculated an Annual Anomaly (AA) of migration and the dates when 10%, 50% and 90% of migrating birds were caught at each station. We modelled AA and the dates of these percentiles of passage for each station against the year and bi-monthly spring, summer and autumn temperatures as explanatory variables in multiple linear regression models. The overall passage (AA) of immature Garden Warblers advanced by 7 days and the dates of the 50th and 90th passage percentiles advanced by 6–11 days. Overall passage, and dates for 50% of passage occurred later the higher summer temperatures rose in Finland. We suggest favourable foraging conditions in warm summers at these breeding grounds and at first stopover sites delayed the passage because these inexperienced birds took advantage of the conditions to accumulate fuel before migrating south. The overall passage, and the dates of 10%, 50% and 90% of autumn passage occurred the earlier the higher were spring temperatures on spring migration route in Italy, and the higher were mean summer temperatures at breeding grounds in southern Sweden and Norway. We suggest a trans-generation carry-over effect, as warm springs encourage early arrival and nesting of returning adults, thus earlier broods and hatching of juveniles, which also grow faster in warm summers. These effects enable immatures to migrate earlier in autumn after a warm breeding season. The long-term increase in Europe’s spring and summer temperatures thus help explain the shift in Garden Warblers’ migration timing

Primary moult of continental Black-tailed Godwits Limosa limosa limosa in the Doñana wetlands, Spain

Capsule: Most Continental Black-tailed Godwits Limosa limosa limosa using the Doñana wetlands during post-breeding migration appear to begin moult before they arrive and suspend moult before they migrate onwards to West Africa. Aims: We aim to describe the primary moult strategies and patterns in the Continental Black-tailed Godwits using the Doñana wetlands, a major passage and wintering area for waterbirds in southern Spain. Methods: Individual godwits were captured, marked and their primary moult was scored in Doñana during the non-breeding season (June–March) in 2011 and 2012. Data from resightings of colour-marked godwits and birds equipped with satellite transmitters were used to estimate stopover duration during post-breeding migration (June–September) to determine if godwits move to West Africa before completing their primary moult. Results: Average primary moult duration was estimated to be 84 days ± 9 se, during 29 June–21 September and did not differ between sexes. Only 2% of individuals were observed with suspended moult. We estimated stopover duration in Doñana to be 13 days ± 2 se before migrating to West Africa. Conclusions: Most godwits stage for about two weeks in the Doñana wetlands during southward migration, moult their primaries and appear to suspend moult before crossing the Sahara. Others may complete their primary moult in Doñana, or elsewhere in Europe and overwinter in Doñana where increasing numbers of godwits have been detected in recent years. A few individuals may finish the moult in Doñana and migrate to West Africa late in the post-breeding season.</p

Primary moult of continental Black-tailed Godwits <i>Limosa limosa limosa</i> in the Doñana wetlands, Spain

Capsule: Most Continental Black-tailed Godwits Limosa limosa limosa using the Doñana wetlandsduring post-breeding migration appear to begin moult before they arrive and suspend moultbefore they migrate onwards to West Africa.Aims: We aim to describe the primary moult strategies and patterns in the Continental Black-tailedGodwits using the Doñana wetlands, a major passage and wintering area for waterbirds in southernSpain.Methods: Individual godwits were captured, marked and their primary moult was scored in Doñanaduring the non-breeding season (June–March) in 2011 and 2012. Data from resightings of colourmarkedgodwits and birds equipped with satellite transmitters were used to estimate stopoverduration during post-breeding migration (June–September) to determine if godwits move toWest Africa before completing their primary moult.Results: Average primary moult duration was estimated to be 84 days ± 9 se, during 29 June–21September and did not differ between sexes. Only 2% of individuals were observed withsuspended moult. We estimated stopover duration in Doñana to be 13 days ± 2 se beforemigrating to West Africa.Conclusions: Most godwits stage for about two weeks in the Doñana wetlands during southwardmigration, moult their primaries and appear to suspend moult before crossing the Sahara. Othersmay complete their primary moult in Doñana, or elsewhere in Europe and overwinter in Doñanawhere increasing numbers of godwits have been detected in recent years. A few individ

Individual variability and versatility in an eco-evolutionary model of avian migration

Seasonal migration is a complex and variable behaviour with the potential to promote reproductive isolation. In Eurasian blackcaps (Sylvia atricapilla), a migratory divide in central Europe separating populations with southwest (SW) and southeast (SE) autumn routes may facilitate isolation, and individuals using new wintering areas in Britain show divergence from Mediterranean winterers. We tracked 100 blackcaps in the wild to characterize these strategies. Blackcaps to the west and east of the divide used predominantly SW and SE directions, respectively, but close to the contact zone many individuals took intermediate (S) routes. At 14.0° E, we documented a sharp transition from SW to SE migratory directions across only 27 (10–86) km, implying a strong selection gradient across the divide. Blackcaps wintering in Britain took northwesterly migration routes from continental European breeding grounds. They originated from a surprisingly extensive area, spanning 2000 km of the breeding range. British winterers bred in sympatry with SW-bound migrants but arrived 9.8 days earlier on the breeding grounds, suggesting some potential for assortative mating by timing. Overall, our data reveal complex variation in songbird migration and suggest that selection can maintain variation in migration direction across short distances while enabling the spread of a novel strategy across a wide range