NEW ASPECTS ON MIGRATORY PHYSIOLOGY OF TRANS-SAHARAN PASSERINE MIGRANTS

Many migratory birds wintering in tropical Africa have to cross the Sahara desert. Although recent research has evaluated the strategies passerine migrants may adopt to cope with trans-Saharan migration, physiological data on migrants in flight or even immediately after landing are almost completely lacking. Therefore, we carried out a pilot study in the Algerian Sahara during autumn 1989 exploiting the fact that many desert migrants are attracted by very small vegetation spots, even a single bush, thus offering the opportunity to get access to birds within a few minutes after their landing. A modern blood autoanalyser which was established in a minitruck enabled concurrent routine measurements of a series of tissue-derived plasma enzymes and chemistries. and whole blood hematocrit and hemoglobin. These values are compared with pre-migratory values obtained in S-Germany in 1990. Elevated levels of plasma glucose, plasma triglycerides, plasma enzymes, and whole blood hematocrit at the desert sites compared with the pre-migratory values indicate the higher metabolic demands of birds in flight, and the use of body proteins during migration. Higher levels of plasma sodium and urea nitrogen in lean than in fat birds reflect dehydration in lean birds which suffer from the lack of appropriate metabolic water production from fat during their migratory flights.