Coming into spring, with the first Willow Warbler songs being heard around Avon recently, this seems like an opportune moment to discuss how birds navigate in order to migrate. Whilst the feat of a tiny Willow Warbler travelling 12,000 km (in the case of Phylloscopus trochilus yakutensis) is humbling and physiologically incredible in its own right, migration becomes even more fascinating when you consider how the birds navigate, without the luxury of GPS, Google Maps and all the other tools humans need to find their way around.
It is thought that some birds use the Sun to navigate whilst there is also evidence that points to Homing Pigeons using olfactory cues to navigate, building up a local “map” based on odours at each location. However, we can’t explain navigation without considering the cognitive abilities of birds and their ability to build mental maps.
Perhaps the most remarkable way this is done is using the Earth’s magnetic field. Juvenile birds of some species on their first migration may have to make the journey alone; clearly there is an innate process at play that means the birds “know” where they are going without ever having made the journey.
Wheatears use magnetoreception to find their way to the UK and beyond |
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Bewick's Swans tend to migrate in family groups |
Perhaps most excitingly, there is scope for more research into this field. Not only have there been improvements in tracking birds using satellite tags (and the new MOTUS technology) but we can look forward to studies that are more sophisticated than putting a Redwing in a magnetic field chamber so we can finally understand a mystery of nature than has puzzled humans for millennia: migration.
Something to Spot: Zugunruhe
With spring and summer on the way, look out for restless behaviour (perhaps in or flying over your gardens) in the last few Redwing and Fieldfare as they prepare to migrate, with birds being more active than normal at dusk and having changed feeding patterns.
References: [1] Wiltschko, W., Munro, U., Ford, H. and Wiltschko, R., 2006. Bird navigation: what type of information does the magnetite-based receptor provide?. Proceedings of the Royal Society B: Biological Sciences, 273(1603), pp.2815-2820. [2] Birkhead, T., 2013. Bird Sense. London: Bloomsbury. [3] Thorup, K., Alerstam, T., Hake, M. and Kjellén, N., 2003. Bird orientation: compensation for wind drift in migrating raptors is age dependent. Proceedings of the Royal Society of London. Series B: Biological Sciences, 270. 4. Hoyo, J., Elliott, A., Sargatal, J. and Baptista, L., 1997. [4] Handbook Of The Birds Of The World. Barcelona: Lynx Edicions, p.649.
George Rabin