Selstam, G., Sondell, J. & Olsson, P. (2015). Wintering area and migration routes for Ortolan Buntings Emberiza hortulana from Sweden determined with light-geologgers. Ornis Svecica 25: 3–14.
PDF in ResearchGate.net
Summary:
The decrease of Ortolan Bunting Emberiza hortulana in Western Europe over the last five decades has caused serious concern for the survival of this species in Sweden. In order to find out the migration routes and wintering location, we equipped several males with geologgers. Our data show annual cycles of migrations routes, wintering grounds and time schedules for seven re-trapped birds. The wintering area in West Africa is savannah woodland in a mountainous landscape in Mali and Guinea. The migration routes follow more or less the great circle between the breeding and wintering areas. Most birds were likely to have passed the well-known Ortolan catching area in les Landes south of Bordeaux in France during autumn migration.
During autumn migration, all the birds made stopovers on the Iberian Peninsula or in Morocco, lasting from 6 to 32 days.
The birds started their spring migration in late March or first half of April. All birds arrived a few days later to stopovers in Morocco or Spain, lasting from 5 to 18 days.
North African Birds 