The dilemma of cross-desert migrants<>9d\stopover or skip a small oasis?

Insectivorous passerines tend to stopover in a desert oasis on their way to their wintering grounds (autumn), but to skip the oasis on their way to their breeding grounds, having crossed the greater part of the Sahara (spring). Stopping-over spring migrants stayed shorter periods, gained less weight and suffered heavier mortality than stopping-over autumn migrants. A selective advantage to reach breeding territories early may override tendencies to stopover due to weather, for refuelling or for rest close to the termination of a strenuous desert crossing. -Authors