| 1. |
- Adamik, Peter, et al.
(författare)
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Barrier crossing in small avian migrants : individual tracking reveals prolonged nocturnal flights into the day as a common migratory strategy
- 2016
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Over decades it has been unclear how individual migratory songbirds cross large ecological barriers such as seas or deserts. By deploying light-level geolocators on four songbird species weighing only about 12 g, we found that these otherwise mainly nocturnal migrants seem to regularly extend their nocturnal flights into the day when crossing the Sahara Desert and the Mediterranean Sea. The proportion of the proposed diurnally flying birds gradually declined over the day with similar landing patterns in autumn and spring. The prolonged flights were slightly more frequent in spring than in autumn, suggesting tighter migratory schedules when returning to breeding sites. Often we found several patterns for barrier crossing for the same individual in autumn compared to the spring journey. As only a small proportion of the birds flew strictly during the night and even some individuals might have flown non-stop, we suggest that prolonged endurance flights are not an exception even in small migratory species. We emphasise an individual’s ability to perform both diurnal and nocturnal migration when facing the challenge of crossing a large ecological barrier to successfully complete a migratory journey.
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| 2. |
- Barboutis, Christos, et al.
(författare)
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Fuelling in front of the barrier-are there age based behavioral differences in Garden Warblers Sylvia borin?
- 2014
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Ingår i: PeerJ. - San Fransisco and London : PeerJ. - 2167-8359. ; 2
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Tidskriftsartikel (refereegranskat)abstract
- Garden Warblers Sylvia borin were studied during autumn stopover in Crete before crossing the barrier of the Mediterranean Sea and the Sahara Desert. Birds followed with transmitters show extensive stopover periods, which were longer in first-year birds, 16 days, compared with adult birds, 14 days. The distribution of body masses from birds trapped in fig trees were used to estimate the departure body mass and the results found indicate that both age categories on average depart with a fuel load close to 100% of lean body mass. The movement of transmitter birds shows differences between first-year and adult birds. Adult birds move further away from the release site and many also left the study area. Several were found settled outside the study area, up to 17 km away, indicating that they regularly make longer stopover movements. It is suggested that this might be a result of that they return to a place where they stayed during an earlier migration. It was shown that stopover site fidelity exists and nine garden warblers were recaptured in the area during a following autumn. The results found highlights the importance of stopover areas close to the Sahara Desert.
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| 3. |
- Barboutis, Christos, et al.
(författare)
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Seasonal differences in energy requirements of Garden Warblers Sylvia borin migrating across the Sahara desert
- 2011
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Ingår i: Ibis. - 0019-1019 .- 1474-919X. ; 153:4, s. 746-754
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Tidskriftsartikel (refereegranskat)abstract
- The Sahara desert acts as an ecological barrier for billions of passerine birds on their way to and from their African wintering areas. The Garden Warbler Sylvia borin is one of the most common migrants involved. We used body mass of this species from Greece in autumn and spring to simulate the desert crossing and to assess how body mass relates to fuel requirement. The flight range estimates were adjusted to the seasonal extent of the desert, 2200 km in autumn and about 2800 km in spring. In autumn, with an average fuel load of about 100% of body mass without fuel, birds were not able to cross the desert in still air, but northerly winds prevail during September and with the average wind assistance only one in 14 was predicted to fail to make the crossing. Body mass data from spring, after the desert crossing, was used to estimate departure body mass from south of the desert. The average wind assistance in spring is close to zero and departure body mass of the average bird arriving at Antikythira, a small Greek island, under such conditions was estimated to be 34.6 g, which corresponded to a fuel load of 116%. Calculations based on 1% body mass loss per hour of flight showed slightly larger body mass loss than that calculated from flight range estimates. The results suggest that passerine birds about to cross the eastern part of the Sahara desert need to attain a larger fuel load in spring than in autumn.
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| 4. |
- Boström, Jannika, et al.
(författare)
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Autumn migratory fuelling : a response to simulated magnetic displacement in juvenile wheatears, Oenathe oenathe
- 2010
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Ingår i: Behavioral Ecology and Sociobiology. - : Springer Science and Business Media LLC. - 0340-5443 .- 1432-0762. ; 64:11, s. 1725-1732
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Tidskriftsartikel (refereegranskat)abstract
- Recent experiments exposing migratory birds to altered magnetic fields simulating geographical displacements have shown that the geomagnetic field acts as an external cue affecting migratory fuelling behaviour. This is the first study investigating fuel deposition in relation to geomagnetic cues in long-distance migrants using the western passage of the Mediterranean region. Juvenile wheatears (Oenanthe oenanthe) were exposed to a magnetically simulated autumn migration from southern Sweden to West Africa. Birds displaced parallel to the west of their natural migration route, simulating an unnatural flight over the Atlantic Ocean, increased their fuel deposition compared to birds experiencing a simulated migration along the natural route. These birds, on the other hand, showed relatively low fuel loads in agreement with earlier data on wheatears trapped during stopover. The experimental displacement to the west, corresponding to novel sites in the Atlantic Ocean, led to a simulated longer distance to the wintering area, probably explaining the observed larger fuel loads. Our data verify previous results suggesting that migratory birds use geomagnetic cues for fuelling decisions and, for the first time, show that birds, on their first migration, can use geomagnetic cues to compensate for a displacement outside their normal migratory route, by adjusting fuel deposition.
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| 5. |
- Briedis, Martins, et al.
(författare)
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Breeding latitude leads to different temporal but not spatial organization of the annual cycle in a long-distance migrant
- 2016
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Ingår i: Journal of Avian Biology. - : Wiley. - 0908-8857 .- 1600-048X. ; 47:6, s. 743-748
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Tidskriftsartikel (refereegranskat)abstract
- The temporal and spatial organization of the annual cycle according to local conditions is of crucial importance for individuals' fitness. Moreover, which sites and when particular sites are used can have profound consequences especially for migratory animals, because the two factors shape interactions within and between populations, as well as between animal and the environment. Here, we compare spatial and temporal patterns of two latitudinally separated breeding populations of a trans-Equatorial passerine migrant, the collared flycatcher Ficedula albicollis, throughout the annual cycle. We found that migration routes and non-breeding residency areas of the two populations largely overlapped. Due to climatic constraints, however, the onset of breeding in the northern population was approximately two weeks later than that of the southern population. We demonstrate that this temporal offset between the populations carries-over from breeding to the entire annual cycle. The northern population was consistently later in timing of all subsequent annual events - autumn migration, non-breeding residence period, spring migration and the following breeding. Such year-round spatiotemporal patterns suggest that annual schedules are endogenously controlled with breeding latitude as the decisive element pre-determining the timing of annual events in our study populations.
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| 6. |
- Fransson, Thord, et al.
(författare)
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Svensk ringmärkning 2019
- 2020
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Ingår i: Fågelåret 2019. - Halmstad : BirdLife Sverige. - 9789188124685 ; , s. 27-37
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Bokkapitel (populärvet., debatt m.m.)
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| 7. |
- Fransson, Thord, et al.
(författare)
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Svensk ringmärkning 2020
- 2021
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Ingår i: Fågelåret 2020. - Halmstad : BirdLife Sverige. - 9789188124708
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Bokkapitel (populärvet., debatt m.m.)
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| 8. |
- Fransson, Thord, et al.
(författare)
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Svensk ringmärkning 2021
- 2022
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Ingår i: Fågelåret 2021. - Halmstad : BirdLife Sverige. - 9789188124722 ; , s. 25-35
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Bokkapitel (populärvet., debatt m.m.)
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| 9. |
- Fransson, Thord, et al.
(författare)
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Svensk ringmärkning 2022
- 2023
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Ingår i: Fågelåret 2022. - Malmö : BirdLife Sverige - Sveriges Ornitologiska Förening. - 9789188124708 ; , s. 29-37
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Bokkapitel (populärvet., debatt m.m.)
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| 10. |
- Henshaw, Ian, 1972-
(författare)
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Avian migration: the role of geomagnetic cues
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The regularity and scale of bird migrations has impressed mankind for generations. Birds rely on an inherited migratory program to guide them during the journey; however, recent evidence suggests that additional external cues are necessary. This thesis concerns how migratory birds use information from the Earth’s geomagnetic field, the role it plays in locating the breeding area and as a cue affecting fuelling behaviour. A displacement experiment with lesser whitethroats (Sylvia curruca) during spring migration indicates, for the first time, that birds include information from the geomagnetic field to locate their breeding area. Birds geomagnetically displaced south of the Swedish breeding area, exhibited consistent northerly orientation, close to the expected migratory direction. Birds displaced north, beyond their previous experience, failed to show a consistent direction of orientation. This suggests that they may have difficulty finding a direction in the absence of other compass cues. Migratory birds must obtain enough fuel and in the right places, e.g. before an ecological barrier, if they are to complete the journey successfully. Young birds on their first migration must do this without previous experience of the journey ahead. Inexperienced thrush nightingales (Luscinia luscinia) increased fuel deposition as expected when given a magnetic field of northern Egypt, their last stopover before the Saharan barrier. A single step change in magnetic field to Egypt resulted in the same change in fuel deposition as previously shown with multiple steps. In contrast, European robins (Erithacus rubecula) experiencing a simulated migration to the wintering area in Spain, where no large fuel loads are needed, showed low fuel deposition rates. This suggests that geomagnetic field information does not produce a general response in fuel deposition in a manner, similar to the way day length triggers migratory activity in autumn, rather birds respond in a biologically relevant way for each species. For both nightingales and robins the patterns of body mass change was unaffected by the time of season in birds experiencing the magnetic treatments. The magnetic field acts, therefore, as an important external cue, overriding the effect of season, helping birds make the right fuelling decisions along the migratory route. Furthermore, food intake was the major reason for the observed increase in fuelling rate compared to control birds. The finding that the magnetic field induces hormonal changes in thrush nightingales gives an indication of the underlying mechanism behind the food intake and resulting body mass changes seen in these experiments.
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