Migratory birds move between their breeding and wintering grounds to take advantage of seasonal fluctuations in resources in these environments. Birds' specific annual cycles, such as breeding and migration, are well timed and adapted to the ecosystems in which they live. When birds deviate from this temporal pattern, they may experience unfavourable conditions, such as food shortages or harsh migratory environments. These conditions can have immediate fitness consequences, i.e. temporal deviation leading directly to death, and delayed fitness consequences, i.e. temporal deviation leading to reduced reproductive success. Studying when birds deviate from the expected temporal pattern is important for identifying the cause(s) of the deviation and predicting the consequences. Most studies of songbird migration have focused on how variation in wintering grounds affects later events in the annual cycle. Few studies have examined whether and how changes in breeding habitat lead to delayed fitness consequences. This is partly because the key features of wintering grounds, i.e. location and habitat quality, can be identified using data loggers and remote sensing, but the key features of the breeding season, e.g. timing of breeding, parental investment and preparation for migration, cannot. The latter represents the transition from the stationary breeding period to the mobile migration period. During this transition, significant behavioural and physiological changes occur in preparation for migration. A study of migratory songbirds showed that birds flew around for several hours at night and then landed back in the breeding area. Four possible reasons for these 'pre-migratory flights' are discussed:

i) practising nocturnal flights,

ii) developing orientation skills,

iii) making a magnetic/landscape map, and

iv) practising assessing meteorological conditions.

Little is known about the spatio-temporal characteristics of these pre-migratory flights. We do not know whether they influence the onset of autumn migration and the return to the breeding grounds, and thus have delayed fitness consequences. The genetic basis of pre-migratory flights has not been investigated. This research proposal will address some of these gaps. We will study the breeding population of Northern Wheatear (Oenanthe oenanthe) on the island of Norderney. The combination of the array of radio receiving stations in the North Sea and radio transmitters operating for > 1 year would allow us to record the spatio-temporal characteristics of pre-migratory flights, the onset of autumn migration and the subsequent timing of arrival at the breeding site. The genetic basis of these behaviours will be studied using hand-reared Northern Wheatears from Norderney under laboratory conditions. The realisation of this project would provide detailed knowledge of pre-migratory flights under natural and laboratory conditions, which is essential for a holistic understanding of bird migration.

Publikations

Züst, Z., Mukhin, A., Taylor, P.D. et al. Pre-migratory flights in migrant songbirds: the ecological and evolutionary importance of understudied exploratory movements. Mov Ecol 11, 78 (2023). https://doi.org/10.1186/s40462-023-00440-y