| 1. |
- Evens, Ruben, et al.
(författare)
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Lunar synchronization of daily activity patterns in a crepuscular avian insectivore
- 2020
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Ingår i: Ecology and Evolution. - : Wiley. - 2045-7758. ; 10:14, s. 7106-7116
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Tidskriftsartikel (refereegranskat)abstract
- Biological rhythms of nearly all animals on earth are synchronized with natural light and are aligned to day-and-night transitions. Here, we test the hypothesis that the lunar cycle affects the nocturnal flight activity of European Nightjars (Caprimulgus europaeus). We describe daily activity patterns of individuals from three different countries across a wide geographic area, during two discrete periods in the annual cycle. Although the sample size for two of our study sites is small, the results are clear in that on average individual flight activity was strongly correlated with both local variation in day length and with the lunar cycle. We highlight the species’ sensitivity to changes in ambient light and its flexibility to respond to such changes in different parts of the world.
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| 2. |
- Norevik, Gabriel, et al.
(författare)
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Wind-associated detours promote seasonal migratory connectivity in a flapping flying long-distance avian migrant
- 2020
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Ingår i: Journal of Animal Ecology. - : Wiley. - 0021-8790 .- 1365-2656. ; 89:2, s. 635-646
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Tidskriftsartikel (refereegranskat)abstract
- It is essential to gain knowledge about the causes and extent of migratory connectivity between stationary periods of migrants to further the understanding of processes affecting populations, and to allow efficient implementation of conservation efforts throughout the annual cycle. Avian migrants likely use optimal routes with respect to mode of locomotion, orientation and migration strategy, influenced by external factors such as wind and topography. In self-powered flapping flying birds, any increases in fuel loads are associated with added flight costs. Energy-minimizing migrants are therefore predicted to trade-off extended detours against reduced travel across ecological barriers with no or limited foraging opportunities. Here, we quantify the extent of detours taken by different populations of European nightjars Caprimulgus europaeus, to test our predictions that they used routes beneficial according to energetic principles and evaluate the effect of route shape on seasonal migratory connectivity. We combined data on birds tracked from breeding sites along a longitudinal gradient from England to Sweden. We analysed the migratory connectivity between breeding and main non-breeding sites, and en route stopover sites just south of the Sahara desert. We quantified each track's route extension relative to the direct route between breeding and wintering sites, respectively, and contrasted it to the potential detour derived from the barrier reduction along the track while accounting for potential wind effects. Nightjars extended their tracks from the direct route between breeding and main non-breeding sites as they crossed the Mediterranean Sea–Sahara desert, the major ecological barrier in the Palaearctic–African migration system. These clockwise detours were small for birds from eastern sites but increased from east to west breeding longitude. Routes of the tracked birds were associated with partial reduction in the barrier crossing resulting in a trade-off between route extension and barrier reduction, as expected in an energy-minimizing migrant. This study demonstrates how the costs of barrier crossings in prevailing winds can disrupt migratory routes towards slightly different goals, and thereby promote migratory connectivity. This is an important link between individual migration strategies in association with an ecological barrier, and both spatially and demographic population patterns.
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