1. Åkesson S, Klaassen R, Holmgren J, Fox JW, Hedenström A (2012) Migration routes and strategies in a highly aerial migrant, the common swift Apus apus, revealed by light-level geolocators. PLoS One 7(7):e41195. doi: 10.1371/journal.pone.0041195
2. BirdLife International (2004) Birds in Europe: population estimates, trends and conservation status, vol 12. BirdLife International, Cambridge
3. BirdLife International (2012) Coracias garrulus. In: IUCN 2014. IUCN red list of threatened species. Version 2014.1. www.iucnredlist.org . Downloaded on 21 June 2014
4. British Antarctic Survey (2010) Geolocator manual v8. British Antarctic Survey, Cambridge
5. BTO (2014) Tracking cuckoos to Africa… and back again. bto.org/cuckoos . Downloaded on 30 April 2014