The pre-migratory flight behaviour in a songbird migrant – spatiotemporal characteristics and potential delayed fitness consequences
Final Report Abstract
Many migratory songbirds undergo remarkable physiological and behavioural changes during the transition from the breeding season to autumn migration, e.g. from being active at day and sleeping at night to performing migratory endurance flights at night. During this transition, juvenile reed warblers (Acrocephalus scirpaceus) were observed already flying at night. Little is known about the frequency, spatiotemporal extent and purpose(s) of such “pre-migratory flights” at night, particularly concerning adult birds. We propose five reasons for such flights: 1) to practise flying at night, 2) to practise assessing meteorological conditions aloft, 3) to practise selecting suitable habitat in darkness, 4) to assess orientation cues and practise orientation skills, and 5) to create magnetic and/or landscape maps. All of these may serve to prepare for migration or the return to their breeding areas next spring. This project addressed some of these knowledge gaps by studying the flight behaviour of radio-tagged juvenile and adult northern wheatears (Oenanthe oenanthe) using a region-scale network of radio-receiving stations in northwest Germany. During the three survey years, we radio-tagged 259 juvenile and 108 adult northern wheatears on the island Norderney. Our results show that both undertake pre-migratory flights, but juveniles perform more and longer flights. This suggests that they practise the flights more intensively than adults. With around 80% of the juveniles and 60% of the adults conducting pre-migratory flights, these figures were lower and higher than expected, respectively. We investigated how consistent behavioural traits related to pre-migratory flights were within nests. Presence/absence, total number of flights per night, flight duration and timing varied considerably within and between nests, with low repeatability estimates (R < 0.35). Repeatability is based on genetic and environmental sources of variance. We assume that the genetic impact on these traits is rather low. This is supported by our “common-garden experiments” demonstrating that hand-raised nestlings did not exhibit consistent patterns of nocturnal migratory restlessness, but the timing of restlessness generally coincided with the seasonal timing of pre-migratory flights in the wild. We demonstrate that pre-migratory flights are not unique to one species or age class, but are a common behaviour. Translocations of animals is considered a crucial conservation measure for preventing the extinction of threatened species. However, they fail because the animals do not stay where released. Studying how animals learn or define where their home is, therefore, essential to correctly time translocations and, consequently, mitigating biodiversity loss.
Publications
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Pre-migratory flights in migrant songbirds: the ecological and evolutionary importance of understudied exploratory movements. Movement Ecology, 11(1).
Züst, Zephyr; Mukhin, Andrey; Taylor, Philip D. & Schmaljohann, Heiko
