Following hybrid eagles to their wintering grounds in Africa.
Bird migration is on of the big mysteries in biology. How do birds know where to fly to each winter? For small songbirds, a genetic basis for migration strategies has been uncovered, perhaps regulated by a so-called ‘migratory gene package‘. In larger birds that travel in flocks, such as geese and cranes, social factors are probably more important as birds learn the migration routes from their parents and relatives.
But how to disentangle genes from culture? To answer this nature-vs-nurture question on bird migration, you can turn to hybrids. One of the first studies to use this strategy focused on European blackcap warblers (Sylvia atricapilla). These small passerines migrate either southwest or southeast. Hybrids between birds that use different migratory strategies direct their migration intermediate, namely south. Similar studies have been conducted on other bird species, such as Swainson’s trush (Catharus ustulatus) and willow warbler (Phylloscopus trochilus).
But what about birds of prey? Researchers have suggested that these big soaring birds learn their migration routes although they usually migrate alone. As the work on passerines indicates, just check the migration of hybrids. And that is exactly what Ülo Väli and his colleagues did: they tracked the migration routes of 62 lesser spotted eagles (A. pomarina), greater spotted eagles (A. clanga) and their hybrids.
These two raptors – that breed in eastern Europe – have very different migration routes. Greater spotted eagles migrate over short distances to winter in southern Eurasia and northeast Africa. The lesser spotted eagle, on the other hand, is a long distance migrant that flies all the way to southern Africa.
The results, based on GPS-telemetry, indicated that the timing of the hybrids was similar to lesser spotted eagles while the wintering destinations were similar to greater spotted eagles. The map below shows the migration routes of lesser spotted eagles (blue), greater spotted eagles (yellow) and their hybrids (red). These mixed patterns suggests that there is some genetic influence on the migration strategy of these eagles. But this doesn’t mean that it is all genetics, the researchers write: ‘these results suggest a strong genetic influence on migration strategy via a trait-dependent dominance effect, although we cannot rule out the contribution of social interactions.’
Väli, U., Mirski, P., Sellis, U., Dagys, M. & Maciorowski, G. (2018) Genetic determination of migration strategies in large soaring birds: evidence from hybrid eagles. Proceedings of the Royal Society B 285,20180855.
This paper has been added to the Accipitriformes page.