Geolocators reveal wintering areas of European Nightjar (Caprimulgus europaeus)

Abstract

Capsule European Nightjars Caprimulgus europaeus breeding in southern England were found to over-winter in the Democratic Republic of Congo. Aims To ascertain the wintering areas and migration routes of European Nightjars breeding in southern England. Methods The wintering areas of three Nightjars were mapped using light geolocation tags (two in 2008 and one in 2010). For one of these birds, details of the timing and route of migration were determined. The impact of the birds' behaviour on location accuracy was measured and data on the timing of emergence and roosting was collected. Results All three Nightjars were found to be wintering in the south and east of the Democratic Republic of Congo, in an area not previously considered to be part of the wintering range of this species. The route of migration differed in each period. Autumn migration was across central Sahara, whereas in spring the route was to the west of the Sahara. Aberrations in the light curve caused by the roosting and emergence of the birds were found to affect the estimated location of the wintering areas, shifting them approximately 1° south, and reducing the estimated accuracy of the locations. The timing of these aberrations showed that roosting and emergence roughly follow the timing of dawn and dusk. Conclusions Current distribution maps for the wintering areas of Nightjars in Africa probably under-represent the true distribution of the species in the continent. The wide dispersal of birds from the same breeding area in the UK may be an indication of mixing of breeding populations during the wintering period. Further study is needed to understand how these results fit into the larger picture of Nightjar migration both from the UK and the wider Eurasian breeding range, and to determine locations of stopovers.