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

Abstract

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.Electronic supplementary materialThe online version of this article (10.1186/s40462-018-0138-0) contains supplementary material, which is available to authorized users.

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

“…As predicted from earlier work (Ticehurst 1936in Williamson 1976Shirihai and Svensson 2018), Willow Warblers from the north-eastern edge of the breeding range are larger compared to the western and north-western edge of the range, with the wing being the single best trait discriminating between all three subspecies. Since yakutensis are migrating longer distances than acredula and trochilus (Sokolovskis et al 2018) this pattern matches Seebohm's rule, predicting that populations with longer migration routes have longer wings (Seebohm 1901). Unlike traits that directly facilitate flying (i.e., wing and tail length), the traits that are more exclusively associated with foraging (i.e., tarsus and bill to head length) did not differ between the Willow Warbler subspecies.…”

“…However, robust population history inferences will require comprehensive data from the entire breeding range of the species, including populations from its easternmost breeding range. Our knowledge to date about the phenotypic characteristics of populations from the eastern range, which undertake the longest migratory journeys (Sokolovskis et al 2018), is based almost exclusively on specimens from museum collections.…”

Migration distance does not predict blood parasitism in a migratory songbird

“…t . yakutensis (13,000 km migration distance one way) and acredula (8,000 km migration distance one way) likely coexist (Sokolovskis et al, ), is a promising location to investigate possible effects of large scale variation in migration distance. However, since future changes to migration distances are likely to occur in small incremental steps, understanding the influence of small variation in migration distance is also important for predictive population dynamics.…”

“…Given that migration distance across populations may vary by as much as 9,000 km for willow warblers (Cramp & Perrins, 1994), subsequent work should seek to incorporate the extremes of individual variation in migration distance. East Africa, where willow warbler subspecies P. t. yakutensis (13,000 km migration distance one way) and acredula (8,000 km migration distance one way) likely coexist (Sokolovskis et al, 2018), is a promising location to investigate possible effects of large scale variation in migration distance.…”

A boreal songbird's 20,000 km migration across North America and the Atlantic Ocean

“…This represents one of the longest recorded round‐trip migrations for a small songbird, up to 21,600 km in total for Blackpolls from Nome (~1,800 km/g; but see Sokolovskis et al. ). Moreover, some of the Blackpoll overwater flight distances (Appendix : Table S1) are on the edge of what was previously thought possible given the fuel requirements for a songbird weighing only ~12 g (Klaassen ).…”