Weather and fuel reserves determine departure and flight decisions in passerines migrating across the Baltic Sea

Sjöberg, Sissel; Alerstam, Thomas; Åkesson, Susanne; Schulz, Axel; Weidauer, Alexander; Coppack, Timothy; Muheim, Rachel

doi:10.1016/j.anbehav.2015.02.015

Cited by 90 publications

(98 citation statements)

References 39 publications

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“…Increased ghrelin will activate the breakdown of lipids in the liver, which is necessary to resume migration because fat is the primary fuel for migrating birds and induces migratory behavior (Zugunruhe). This interpretation fits very well with a number of studies that demonstrated that fat stores are among the best physiological predictors of stopover duration (3)(4)(5)(6)(7)(8)(9)(10)(11)(12).…”

Section: Discussionsupporting

confidence: 88%

“…However, the final decision to resume migration depends on the interplay between environmental conditions, the endogenous program, and the physiological condition of an individual. Theory predicts that stopover decisions depend on amount and rate of deposition of energy stores (1,2), and empirical findings have confirmed this hypothesis (3)(4)(5)(6)(7)(8)(9)(10)(11)(12). The big and yet unanswered question is, How do birds know that they are ready to depart?…”

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confidence: 99%

“…Previous work has shown that fat stores are the best predictor for migratory disposition and stopover duration: Birds with larger subcutaneous (s.c.) fat stores show more migratory restlessness in captivity (8,10,13,14), stay shorter times at stopover sites (9,11), and migrate faster (12). Because birds fuel their migratory flights primarily through fatty acid metabolism (15)(16)(17), we expect that factors reflecting fuel load or the energetic condition must be involved in the behavioral switch between resting at stopover sites and resuming migration.…”

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Ghrelin affects stopover decisions and food intake in a long-distance migrant

Goymann

Lupi

Kaiya

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Billions of birds migrate long distances to either reach breeding areas or to spend the winter at more benign places. On migration, most passerines frequently stop over to rest and replenish their fuel reserves. To date, we know little regarding how they decide that they are ready to continue their journey. What physiological signals tell a bird's brain that its fuel reserves are sufficient to resume migration? A network of hormones regulates food intake and body mass in vertebrates, including the recently discovered peptide hormone, ghrelin. Here, we show that ghrelin reflects body condition and influences migratory behavior of wild birds. We measured ghrelin levels of wild garden warblers (Sylvia borin) captured at a stopover site. Further, we manipulated blood concentrations of ghrelin to test its effects on food intake and migratory restlessness. We found that acylated ghrelin concentrations of garden warblers with larger fat scores were higher than those of birds without fat stores. Further, injections of unacylated ghrelin decreased food intake and increased migratory restlessness. These results represent experimental evidence that appetite-regulating hormones control migratory behavior. Our study lays a milestone in migration physiology because it provides the missing link between ecologically dependent factors such as condition and timing of migration. In addition, it offers insights in the regulation of the hormonal system controlling food intake and energy stores in vertebrates, whose disruption causes eating disorders and obesity.bird migration | ghrelin | migratory restlessness | food intake | stopover E very year, billions of birds migrate long distances to either reach areas offering favorable wintering conditions or breeding grounds that thrive with food during the reproductive season. For most small passerines, migration involves frequent stopovers to rest and refuel. During stopover, birds are exposed to fluctuating environmental conditions, including weather and food, which influence the duration of their stay. However, the final decision to resume migration depends on the interplay between environmental conditions, the endogenous program, and the physiological condition of an individual. Theory predicts that stopover decisions depend on amount and rate of deposition of energy stores (1, 2), and empirical findings have confirmed this hypothesis (3-12). The big and yet unanswered question is, How do birds know that they are ready to depart? That is, which physiological signals tell the brain that the fuel reserves are sufficient to resume migration? This link that connects physiological condition and brain is still unknown.Previous work has shown that fat stores are the best predictor for migratory disposition and stopover duration: Birds with larger subcutaneous (s.c.) fat stores show more migratory restlessness in captivity (8,10,13,14), stay shorter times at stopover sites (9, 11), and migrate faster (12). Because birds fuel their migratory flights primarily through fatty acid metabolism (15-...

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Section: Discussionsupporting

confidence: 88%

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confidence: 99%

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confidence: 99%

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Ghrelin affects stopover decisions and food intake in a long-distance migrant

Goymann

Lupi

Kaiya

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…The clock that times Zugunruhe is highly responsive to nutritional state and ticks more slowly than the daytime clock 38 . Although captivity findings generally corresponded well with field data, recent studies also revealed differences: whereas in captive migrants, Zugunruhe usually sets in shortly after sunset 39 , free-living migrants adjusted the timing of departure depending on environmental factors and their body condition [40][41][42][43] . Furthermore, whereas in captivity, autumn Zugunruhe usually builds up by a gradual activity shift into the night, a recent study on free-living short-distance migrants revealed that the birds left instantaneously during their first restless night 44 .…”

Section: Departing In Time In Anticipation Of Future Environmental Csupporting

confidence: 59%

Timing avian long-distance migration: from internal clock mechanisms to global flights

Åkesson

Ilieva

Karagicheva

et al. 2017

Phil. Trans. R. Soc. B

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101

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Please refer to our instructions for authors for full details on manuscript preparation. Please note that this template should act as a guide on content, but doesn't necessarily need to be followed for style and formatting. Our typesetters will set your manuscript into house style after acceptance.*Author for correspondence (Susanne.akesson@biol.lu.se). †Present address: Department of Biology, Lund University, Ecology Building, SE-223 62 Lund, Sweden 2 Summary Migratory birds regularly perform impressive long-distance flights, which are timed relative to the anticipated environmental resources at destination areas that can be several thousand kilometres away. Timely migration requires diverse strategies and adaptations that involve an intricate interplay between internal clock mechanisms and environmental conditions across the annual cycle. Here we review what challenges birds face during long migrations to keep track of time as they exploit geographically distant resources that may vary in availability and predictability, and summarise the clock mechanisms that enable them to succeed. We examine the following challenges: departing in time for spring and autumn migration, in anticipation of future environmental conditions; using clocks on the move, for example for orientation, navigation, and stopover; strategies of adhering to, or adjusting the time program while fitting their activities into an annual cycle; and keeping pace with a world of rapidly changing environments. We then elaborate these themes by case studies representing long-distance migrating birds with different annual movement patterns and associated adaptations of their circannual programs. We discuss the current knowledge on how endogenous migration programs interact with external information across the annual cycle, how components of annual cycle programs encode topography and range expansions, and how fitness may be affected when mismatches between timing and environmental conditions occur. Lastly, we outline open questions and propose future research directions. Non-technical summaryMigratory birds perform impressive long-distance flights, timed relative to the availability of resources in different geographical areas. To manage this birds use different strategies including an interplay between internal clock mechanisms and environmental conditions across the annual cycle. Here we review what challenges birds face during long migrations to keep track of time as they exploit geographically distant resources that may vary in availability and predictability, and summarise the clock mechanisms that enable them to meet these challenges. We discuss how range expansions affect components of annual cycle programs, and how mismatches between timing and environment may affect reproductive success.3

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“…Studying bat behaviour therefore should be done at three different spatial scales: on the scale of an larger scale (Lagerveld et al in prep, Francis et al 2016, Janssen et al 2016, Kays et al 2011, Körner et al 2010, Rerucha et al 2014, Sjöberg et al 2015, Smolinsky et al 2013 3) Can reliable estimates be obtained of the number of bats which pass through offshore wind farms and over the southern North Sea in general, when behavioural data is combined with bat detector data?…”

Section: Discussionmentioning

confidence: 99%