ABS 2022
Fuel deposition and stopover duration strategy of autumn migrating passerines at a desert edge
Nir Sapir. Dept Evolutionary & Environmental Biology, University of Haifa, Haifa, N/A, Israel

Fuel deposition rate at stopover may determine bird departure fuel load in time-minimizing migrating birds. Yet, near ecological barriers birds may depart with just enough fuel to cross the barrier, thus reaching a threshold of fuel load regardless of fuel deposition rate. To test these contrasting predictions we studied fifteen autumn migrating Red-backed shrikes (Lanius collurio) in Israel before they departed for a ~2,000 km journey across the Sahara Desert. We combined daily body mass measurements with movement data from the ATLAS telemetry system. We found that bird condition at departure depended on the rate of fuel deposition, as predicted by the time-minimization hypothesis. Furthermore, birds that arrived with low body mass and gained fuel at low rate remained longer in stopover before the cross-desert flight. Our work suggests that even near a wide ecological barrier, departure fuel load is sensitive to the rate of fuel deposition and that birds do not accumulate fuel to a certain threshold that would allow them to cross the desert. We propose that our findings reflect high between-individual variation in migratory performance with likely consequences for survival.