Figure 6

Stopover-site information can fine-tune arrival at variable breeding grounds. LEFT: A) Expected breeding success depends on timing, with the peak of the curve indicating the optimal arrival time T*. Environmental conditions vary between early, intermediate, and late years, with the probability of each year type given by the bars and the right-hand scale. B) The long-term expected fitness for a given arrival date is the probability that a certain year type occurs multiplied by the fledging success in that type of year. The probabilities for each year type are here laid above each other for each date, not superimposed. CENTRE: If no information available, then the best option is to arrive at the date that represents the peak of the long-term fitness curve (panel D). In the most common intermediate years this is the best option (orange arrow in panel C), but in early or late years there is a considerable fitness loss (blue and green arrows). Fitness W is the achieved fitness in each year type, indicated by the arrow, weighted by the probability of occurrence of the year type from panel A. RIGHT: Cues at a stopover site can guide arrival on breeding grounds at more appropriate times for each breeding season. In the cue-response (panel F), a cue that can be observed at the stopover site predicts what type of year it is and thus the optimal timing of migration. A low cue value from F) indicates an early year (blue line), and, compared to the situation where information is ignored, a higher fitness can be obtained in early years (blue arrow in panel E). Conversely, with late years (in green). The value of stopover-site information is the increased fitness in early and late years in panel E vs. C.