Pay-offs and penalties of competing migratory schedules

• Published in: Oikos
• Main Authors: Drent, R.H., Both, C., Green, M., Madsen, J., Piersma, T.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2003
• Subjects: Climate change
• Online Access: https://pure.knaw.nl/portal/en/publications/c06bf513-e89e-4977-9172-0a23c1269a42; https://doi.org/10.1034/j.1600-0706.2003.12274.x; https://hdl.handle.net/20.500.11755/c06bf513-e89e-4977-9172-0a23c1269a42

We relate variation in the timing of arrival by migrating birds breeding at northerly latitudes to individual differences in the prior accumulation of energy stores. Balancing starvation risks early in the season against the almost universal declining trend in reproductive prospects with advancing date is seen as an individual decision with fitness consequences. We review three studies implicating events at the staging sites or in winter in setting the individual migratory schedule. Climate change influences the timetable of a pied flycatcher (Ficedula hypoleuca) population breeding in The Netherlands and wintering in West Africa, followed since 1960. Mean air temperature in the period mid April-mid May (arrival and laying) increased and laying date advanced by 10 days. Still, in recent years most birds did not lay early enough to maximise fitness (determined by recruitment and parental survival) whereas many parents achieved this goal in 1980-1985. As the flycatchers have not started to arrive earlier, some ecological constraint further upstream is postulated (possibly the hurdle of the crossing of Sahara and Mediterranean). The ability to follow individual migrants provides a second avenue to assess the fitness implications of migratory schedules. Thus, brightly coloured male bar-tailed godwits (Limosa lapponica) captured in the Dutch Wadden Sea (the intermediate staging site linking a West African wintering area with breeding sites in arctic Russia) and traced with miniature radio-transmitters did not depart early. The 'best' males (with bright breeding plumage) were picked up by the listening stations in Sweden 650 km further along the migratory route ten days later than the paler individuals. If early arrival confers the competitive advantage of prior occupancy but increases mortality, the 'best' males may be able to afford arriving later and thus avoid some of the survival costs. Return rate of the 'bright' males to the staging site in later seasons was indeed higher than for the 'pale', early males. ...