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Ecological factors influence timing of departures in nocturnally migrating songbirds at Falsterbo, Sweden

Sjöberg, Sissel LU ; Alerstam, Thomas LU ; Åkesson, Susanne LU and Muheim, Rachel LU (2017) In Animal Behaviour 127. p.253-269
Abstract

Most songbirds depart from stopover sites after sunset and migrate during the night. Several recent studies have reported larger variation in departure time than previously thought; yet, it is still unclear which factors govern departure timing. We investigated the departure timing of four species of nocturnally migrating songbirds using an automated radiotelemetry system at Falsterbo peninsula in southwest Sweden. We made a comprehensive analysis to test a range of factors that have been hypothesized to affect departure timing of nocturnal migrants, such as night duration, season, sun elevation and the birds' intrinsic and environmental conditions. We hypothesized that birds in good condition (large fuel reserves) and under... (More)

Most songbirds depart from stopover sites after sunset and migrate during the night. Several recent studies have reported larger variation in departure time than previously thought; yet, it is still unclear which factors govern departure timing. We investigated the departure timing of four species of nocturnally migrating songbirds using an automated radiotelemetry system at Falsterbo peninsula in southwest Sweden. We made a comprehensive analysis to test a range of factors that have been hypothesized to affect departure timing of nocturnal migrants, such as night duration, season, sun elevation and the birds' intrinsic and environmental conditions. We hypothesized that birds in good condition (large fuel reserves) and under advantageous flight conditions would depart sooner after sunset, in the expected migratory direction. Our analyses showed that the birds departed sooner after sunset during spring than autumn, and different species departed at different times in relation to sunset. In addition, birds departed earlier when nights were shorter, suggesting that night duration is an important factor that may drive much of the observed timing differences between seasons and species. Lean birds delayed their departures compared to fat individuals. When birds experienced favourable wind conditions (tail wind or weak winds) at sunset, they departed earlier. Thus, it appears that the decision to take off for a long-distance flight depends on both body condition and wind conditions. Timing of departure was not correlated with sun elevation, which would have been expected if availability of specific orientation cues (sun, skylight polarization pattern, stars) acted as triggers for departures. These results stress high flexibility and adaptive responses to a complex of ecological factors as the determinants for timing of nocturnal flights in songbirds.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
bird migration, departure timing, passerines, radiotelemetry, songbirds, stopover
in
Animal Behaviour
volume
127
pages
17 pages
publisher
Elsevier
external identifiers
  • scopus:85018487043
  • wos:000402702900028
ISSN
0003-3472
DOI
10.1016/j.anbehav.2017.03.007
language
English
LU publication?
yes
id
f91837e2-e973-4d34-9067-5def75699d3e
date added to LUP
2017-05-17 14:16:20
date last changed
2017-09-18 11:36:06
@article{f91837e2-e973-4d34-9067-5def75699d3e,
  abstract     = {<p>Most songbirds depart from stopover sites after sunset and migrate during the night. Several recent studies have reported larger variation in departure time than previously thought; yet, it is still unclear which factors govern departure timing. We investigated the departure timing of four species of nocturnally migrating songbirds using an automated radiotelemetry system at Falsterbo peninsula in southwest Sweden. We made a comprehensive analysis to test a range of factors that have been hypothesized to affect departure timing of nocturnal migrants, such as night duration, season, sun elevation and the birds' intrinsic and environmental conditions. We hypothesized that birds in good condition (large fuel reserves) and under advantageous flight conditions would depart sooner after sunset, in the expected migratory direction. Our analyses showed that the birds departed sooner after sunset during spring than autumn, and different species departed at different times in relation to sunset. In addition, birds departed earlier when nights were shorter, suggesting that night duration is an important factor that may drive much of the observed timing differences between seasons and species. Lean birds delayed their departures compared to fat individuals. When birds experienced favourable wind conditions (tail wind or weak winds) at sunset, they departed earlier. Thus, it appears that the decision to take off for a long-distance flight depends on both body condition and wind conditions. Timing of departure was not correlated with sun elevation, which would have been expected if availability of specific orientation cues (sun, skylight polarization pattern, stars) acted as triggers for departures. These results stress high flexibility and adaptive responses to a complex of ecological factors as the determinants for timing of nocturnal flights in songbirds.</p>},
  author       = {Sjöberg, Sissel and Alerstam, Thomas and Åkesson, Susanne and Muheim, Rachel},
  issn         = {0003-3472},
  keyword      = {bird migration,departure timing,passerines,radiotelemetry,songbirds,stopover},
  language     = {eng},
  month        = {05},
  pages        = {253--269},
  publisher    = {Elsevier},
  series       = {Animal Behaviour},
  title        = {Ecological factors influence timing of departures in nocturnally migrating songbirds at Falsterbo, Sweden},
  url          = {http://dx.doi.org/10.1016/j.anbehav.2017.03.007},
  volume       = {127},
  year         = {2017},
}