Figure 1.

Examples of three pied flycatchers (male: F272/F291; female: F384) that used diurnal flight twice a year when facing ecological barriers, like the Sahara. Light and temperature profiles (a) show 2 days before, 2 days during and 2 days after diurnal flight in autumn and spring, and changes in longitude positions (b) across 2013–2014. Grey lines indicate diurnal flight (periods). Temperatures (in a) are approximate changes in ambient temperature rather than being absolute measures and were saved at the end of each 4 h period.