Do blackcaps Sylvia atricapilla stopping over at a locality from Southern Iberia refuel for crossing the Sahara?

Migrants that cross large inhospitable areas must accumulate large loads of fuel to reach their destinations successfully. The stopover strategies of European long-distance migrants are relatively well studied for species that overwinter in tropical Africa, but less so for those that overwinter mainly around the Mediterranean and of which only a fraction reach tropical Africa. Our aim here was to analyse whether blackcaps Sylvia atricapilla stopping over in southern Iberia gain sufficient fuel in this region to be able to reach tropical Africa. Blackcaps were mistnetted during the autumn migration period of 2005 at a locality in Northern Iberia (Loza) and another in Southern Iberia (Doñna). Blackcaps at Doñana had lower fuel loads and a slower fuel deposition rate than at Loza, and the estimated flight ranges from both sites were insufficient to reach tropical Africa. The stopover duration was similar at both localities. If trans-Saharan birds occurred at Doñana, they would need to refuel at other stopover sites in Southern Iberia or in Northern Africa before crossing the Sahara. The circum-Mediterranean region may hence be of great importance for the fraction of the blackcap population that overwinters in tropical Africa.