Does the length of the night affect the timing of nocturnal departures in a migratory songbird?

Fabbri, Muller; Rüppel, Georg; Schmaljohann, Heiko

doi:10.1016/j.anbehav.2018.05.018

Cited by 13 publications

(9 citation statements)

References 51 publications

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“…Birds were equipped with individually coded radio-telemetry transmitters of type NTQB (Lotek Wireless Inc., Newmarket, ON, Canada) directly after catching. Leg loop harnesses consisted of non UV resistant elastic rubber band and were expected to fall off the bird after a few weeks as the rubber soon gets brittle [41]. Tags including harnesses weighted about 0.29 g. Movements were subsequently tracked by an array of automated radio-telemetry receivers covering the German North Sea coastline and islands located in the German Bight (Fig.…”

Section: Methodsmentioning

confidence: 99%

To cross or not to cross – thrushes at the German North Sea coast adapt flight and routing to wind conditions in autumn

2019

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BackgroundAlthough many aspects of passerine migration are genetically determined, routing appears to be flexibly adjusted to the conditions experienced on each individual journey. This holds especially true for routing decisions taken when confronted with large bodies of water. Once taken, these decisions can be hardly altered or revised. In this paper, we analysed stopover and routing decisions taken by three species of thrushes, blackbirds, redwings and song thrushes, at the German North Sea coast.MethodsBirds were equipped with radio-telemetry tags at stopover sites along the coast during autumn migration and subsequently tracked by an automated receiver network covering the coastline and islands of the German Bight.ResultsThe thrushes resumed migration in nights with a favourable northward wind component and clear skies. About 40% of the tagged individuals have taken an offshore instead of an alongshore oriented flight route. Routing decisions were influenced by the strength of the eastward wind component with offshore oriented flights taking place primarily under weak winds or winds blowing towards the west. Thrushes that took an offshore oriented route stopped over at the coast longer than those flying alongshore. Interestingly, offshore as well as alongshore oriented flights co-occurred within single nights and under comparable weather conditions.ConclusionsMigratory flight and routing decisions of thrushes at the German North Sea coast are highly dependent on weather, in particular wind. Still, we found evidence that weather may not be the sole reason for individual routes taken. Physical condition, morphology or animal personality lend themselves as possible additional factors of influence. Enabling a more detailed understanding of thrush migration over and along the German North Sea, our data help to better judge risks that migratory birds are facing when en route conditions are altered, for example by artificial obstacles such as offshore wind turbines.Electronic supplementary materialThe online version of this article (10.1186/s40462-019-0173-5) contains supplementary material, which is available to authorized users.

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Section: Methodsmentioning

confidence: 99%

To cross or not to cross – thrushes at the German North Sea coast adapt flight and routing to wind conditions in autumn

2019

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“…Since the majority of land birds migrate at night, we focused on nocturnal migration in our study. Nocturnal migrants generally depart on their migration journey around sunset (Alerstam , Åkesson et al ), but this can vary slightly among nights with different length, different species, birds with different body conditions and between seasons (Sjöberg et al , Müller et al , , b). We selected tracks that were recorded by the vertical radar from sunset up to one hour before sunrise of the following day and calculated the total number of tracks per night within the determined detection range as a measure of migration intensity.…”

Section: Methodsmentioning

confidence: 99%

Winds at departure shape seasonal patterns of nocturnal bird migration over the North Sea

Bradarić

Bouten

Fijn

et al. 2020

Journal of Avian Biology

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On their migratory journeys, terrestrial birds can come across large inhospitable areas with limited opportunities to rest and refuel. Flight over these areas poses a risk especially when wind conditions en route are adverse, in which case inhospitable areas can act as an ecological barrier for terrestrial migrants. Thus, within the east-Atlantic flyway, the North Sea can function as an ecological barrier. The main aim of this study was to shed light on seasonal patterns of bird migration in the southern North Sea and determine whether departure decisions on nights of intense migration were related to increased wind assistance. We measured migration characteristics with a radar that was located 18 km off the NW Dutch coast and used simulation models to infer potential departure locations of birds on nights with intense nocturnal bird migration. We calculated headings, track directions, airspeeds, groundspeeds on weak and intense migration nights in both seasons and compared speeds between seasons. Moreover, we tested if departure decisions on intense migration nights were associated with supportive winds. Our results reveal that on the intense migration nights in spring, the mean heading was towards E, and birds departed predominantly from the UK. On intense migration nights in autumn, the majority of birds departed from Denmark, Germany and north of the Netherlands with the mean heading towards SW. Prevailing winds from WSW at departure were supportive of a direct crossing of the North Sea in spring. However, in autumn winds were generally not supportive, which is why many birds exploited positive wind assistance which occurred on intense migration nights. This implies that the seasonal wind regimes over the North Sea alter its migratory dynamics which is reflected in headings, timing and intensity of migration.

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“…As all ten warbler species probably migrate exclusively during the night (Wang et al 2019), flow assistance was estimated for the average night length the birds experienced during the field study, which was eleven hours. The assumption that the warblers migrated only during the night seems reasonable, because most songbirds setting off with high energy stores and towards the seasonally appropriate migratory direction start their migratory flight bout shortly after sunset (Müller et al 2016(Müller et al , 2018 and terminate it shortly before sunrise (Liechti et al 2018). Thus, "hours" was set to 11 and "evaluation.interval" to 220 min (3 downloads per night).…”

Section: Flight Range Estimationmentioning

confidence: 99%

Seasonal and diurnal increases in energy stores in migratory warblers at an autumn stopover site along the Asian–Australasian flyway

2019

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The authors want to thank Sergei M. Smirenski and the staff of Muraviovka Park as well as all volunteers who participated in the bird ringing activities. An earlier version of this manuscript was improved by comments of Franz Bairlein and Dan Chamberlain and two anonymous reviewers. Our study was carried out in accordance to the legal and ethical requirements for animal research and welfare in the Russian Federation. Birds were captured and marked with permission from the Russian Bird Ringing Centre.

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Does the length of the night affect the timing of nocturnal departures in a migratory songbird?

Cited by 13 publications

References 51 publications

To cross or not to cross – thrushes at the German North Sea coast adapt flight and routing to wind conditions in autumn

To cross or not to cross – thrushes at the German North Sea coast adapt flight and routing to wind conditions in autumn

Winds at departure shape seasonal patterns of nocturnal bird migration over the North Sea

Seasonal and diurnal increases in energy stores in migratory warblers at an autumn stopover site along the Asian–Australasian flyway

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