| 1. |
- Alerstam, Thomas, et al.
(författare)
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Flight speeds among bird species : allometric and phylogenetic effects.
- 2007
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Ingår i: PLoS biology. - : Public Library of Science (PLoS). - 1544-9173 .- 1545-7885. ; 5:8, s. e197-
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Tidskriftsartikel (refereegranskat)abstract
- Flight speed is expected to increase with mass and wing loading among flying animals and aircraft for fundamental aerodynamic reasons. Assuming geometrical and dynamical similarity, cruising flight speed is predicted to vary as (body mass)(1/6) and (wing loading)(1/2) among bird species. To test these scaling rules and the general importance of mass and wing loading for bird flight speeds, we used tracking radar to measure flapping flight speeds of individuals or flocks of migrating birds visually identified to species as well as their altitude and winds at the altitudes where the birds were flying. Equivalent airspeeds (airspeeds corrected to sea level air density, Ue) of 138 species, ranging 0.01-10 kg in mass, were analysed in relation to biometry and phylogeny. Scaling exponents in relation to mass and wing loading were significantly smaller than predicted (about 0.12 and 0.32, respectively, with similar results for analyses based on species and independent phylogenetic contrasts). These low scaling exponents may be the result of evolutionary restrictions on bird flight-speed range, counteracting too slow flight speeds among species with low wing loading and too fast speeds among species with high wing loading. This compression of speed range is partly attained through geometric differences, with aspect ratio showing a positive relationship with body mass and wing loading, but additional factors are required to fully explain the small scaling exponent of Ue in relation to wing loading. Furthermore, mass and wing loading accounted for only a limited proportion of the variation in Ue. Phylogeny was a powerful factor, in combination with wing loading, to account for the variation in Ue. These results demonstrate that functional flight adaptations and constraints associated with different evolutionary lineages have an important influence on cruising flapping flight speed that goes beyond the general aerodynamic scaling effects of mass and wing loading.
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| 2. |
- 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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| 3. |
- Klaassen, Raymond, et al.
(författare)
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Geographical and temporal flexibility in the response to crosswinds by migrating raptors.
- 2011
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Ingår i: Proceedings of the Royal Society B: Biological Sciences. - : The Royal Society. - 1471-2954 .- 0962-8452. ; 278, s. 1339-1346
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Tidskriftsartikel (refereegranskat)abstract
- Wind and ocean currents may potentially have important effects on travelling animals, as an animal which does not respond to lateral flow will be drifted from its intended direction of movement. By analysing daily movements of migrating ospreys Pandion haliaetus and marsh harriers Circus aeruginosus, as recorded by satellite telemetry, in relation to global wind data, we showed that these raptors allow on average 47 per cent drift. Furthermore, our analyses revealed significant geographical and temporal variation in the response to crosswinds. During some parts of the migration, the birds drifted and in other parts they compensated or even overcompensated. In some regions, the response of marsh harriers depended on the wind direction. They drifted when the wind came from one side and (over)compensated when the wind came from the opposite side, and this flexible response was different in different geographical regions. These results suggest that migrating raptors modulate their response to crosswinds at different places and times during their travels and show that individual birds use a much more varied repertoire of behavioural responses to wind than hitherto assumed. Our results may also explain why contrasting and variable results have been obtained in previous studies of the effect of wind on bird migration.
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| 4. |
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| 5. |
- Alerstam, Thomas, et al.
(författare)
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Migration Along Orthodromic Sun Compass Routes by Arctic Birds
- 2001
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 291:5502, s. 300-303
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Tidskriftsartikel (refereegranskat)abstract
- Flight directions of birds migrating at high geographic and magnetic latitudes can be used to test bird orientation by celestial or geomagnetic compass systems under polar conditions. Migration patterns of arctic shorebirds, revealed by tracking radar studies during an icebreaker expedition along the Northwest Passage in 1999, support predicted sun compass trajectories but cannot be reconciled with orientation along either geographic or magnetic loxodromes (rhumb lines). Sun compass routes are similar to orthodromes (great circle routes) at high latitudes, showing changing geographic courses as the birds traverse longitudes and their internal clock gets out of phase with local time. These routes bring the shorebirds from high arctic Canada to the east coast of North America, from which they make transoceanic flights to South America. The observations are also consistent with a migration link between Siberia and the Beaufort Sea region by way of sun compass routes across the Arctic Ocean.
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| 6. |
- Alerstam, Thomas, et al.
(författare)
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Temporal and spatial patterns of repeated migratory journeys by ospreys
- 2006
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Ingår i: Animal Behaviour. - : Elsevier BV. - 1095-8282 .- 0003-3472. ; 71:3, s. 555-566
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Tidskriftsartikel (refereegranskat)abstract
- We used satellite-tracking data from repeated journeys between Europe and West Africa by the same osprey, Pandion haliaetus, individuals to test whether the timing of migration differs between spring and autumn and whether landmarks and stopover goal areas are important for navigation. The timing of migration varied more in autumn than in spring, owing to significant differences between individuals (related to sex) in autumn migration dates. Autumn journeys were significantly slower than spring journeys because they included more stopover days. The difference may be explained by environmental conditions restricting the timing of migration in spring, by differences in opportunities to deposit fuel prior to departure, and by differences in expected changes in foraging/fuelling conditions along the route. Flight paths from repeated journeys by the same individual were often 120-405 km apart (maximum east-west separation 1400 km). These distances exceed the expected normal range of vision, suggesting that the ospreys did not find their way by following familiar landmarks. Flight paths converged in some regions, indicating the existence of up to three intermediary goal areas along the route of individual birds. Between these goal regions route fidelity was low, and the ospreys could find the next goal region after extensive deviation, presumably by map-based navigation and possibly in combination with path integration. (c) 2006 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All tights reserved.
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| 7. |
- Brattström, Oskar, et al.
(författare)
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Effects of wind and weather on red admiral, Vanessa atalanta, migration at a coastal site in southern Sweden
- 2008
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Ingår i: Animal Behaviour. - : Elsevier BV. - 1095-8282 .- 0003-3472. ; 76, s. 335-344
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Tidskriftsartikel (refereegranskat)abstract
- Each autumn, large numbers of red admirals migrate throughout northern Europe,flying south, to reach areas with conditions suitable for surviving the winter. We observed the visible butterfly migration at Falsterbo peninsula, the southwesternmost point in Sweden, where red admirals are seen most autumns. ying towards the Danish coast on their way to more southern parts of Europe. Weather parameters from a local weather station were used to analyse what factors are important for red admiral migration across the sea. Wind direction was among the important weather variables affecting the initiation of the migratory departure; most other studies of butterfly migration reported no large effect of wind direction. This difference is probably because the butterflies in our study were about to cross open sea for more than 20 km, whereas most previous studies were from inland locations where butterflies could avoid wind effects by. ying close to the ground or on the lee side of topographical features. Other important weather variables affecting red admiral migration at Falsterbo were low wind speed and clear skies. The flight direction at Falsterbo was towards the west, which is in contrast to the southward direction generally reported during autumn migration in this species. This is probably because the red admirals followed both the local topography and the closest route to land on the other side and therefore deviated from the normally preferred direction to minimize flight over open water. (c) 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
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| 8. |
- Clausen, P, et al.
(författare)
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Energy limitations for spring migration and breeding: the case of brent geese Branta bernicla tracked by satellite telemetry to Svalbard and Greenland
- 2003
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 103:2, s. 426-445
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Konferensbidrag (refereegranskat)abstract
- Brent geese were tracked by satellite telemetry from spring staging areas in Denmark to Arctic breeding areas in Svalbard and Greenland in 1997 and 2001. From estimated departure masses and carcass analysis we used flight mechnical theory to estimate maximum flight ranges of both sexes, and remaining stores of fat and protein upon arrival in females. Model predictions suggested that all birds but one exceptionally thin male could easily reach Svalbard, but that approximately one third of the males and half of the females would have problems with flying to Greenland. Nevertheless, some birds even flew longer than the models predicted. In addition, females predicted to be capable of making the flight to Greenland, were predicted to arrive almost lean of fat. This contradicts our expectation that these birds are capital breeders - that they depend on endogenous stores of fat and protein when initiating and incubating their eggs. We discuss how the Greenland breeding sub-population during 1985-1998 has been able to grow at the same rate as the sub-population breeding in Svalbard, despite the added flight distance of 700-1000 km, and despite the birds predicted shortage of fat stores on arrival. We suggest four hypotheses that alone or in combination could explain the discrepancy between model predictions and observations. These are that most birds: (1) refuel on stop-overs in Spitsbergen en route to Greenland; (2) pick favourable tail-winds enabling them to reduce flight costs; (3) fly in formation and thereby save energy; and/or (4) undergo gut atrophy immediately prior to departure, and use the nutrients mobilised by catabolism of the digestive system to build larger pectoral muscles. The latter option would both reduce their airframe fraction, and increase their fat and flight-muscle fractions, enabling them to fly longer. We conclude that the latter option seems less likely to operate in brent geese.
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| 9. |
- Green, Martin, et al.
(författare)
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Dark-bellied Brent Geese Branta bernicla bernicla, as recorded by satellite telemetry, do not minimize flight distance during spring migration
- 2002
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Ingår i: Ibis. - : Wiley. - 0019-1019. ; 144:1, s. 106-121
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Tidskriftsartikel (refereegranskat)abstract
- Nine Dark-bellied Brent Geese Branta bernicla bernicla were equipped with satellite transmitters during spring staging in the Dutch Wadden Sea in 1998 and 1999. The transmitters (in all cases less than 3% of body mass) were attached to the back by a flexible elastic harness. One juvenile female was tracked to the Yamal peninsula in 1998. Eight adult males were selected from a single catch of 75 to span the range of body mass observed on the date of capture (11 May 1999) and all but the lightest individual completed the first lap of the migratory flight to the White Sea, Russia, according to the time schedule normal for this species. Six birds were successfully tracked to Taymyr for a total distance averaging 5004 km (range 4577-5164) but judging from later movements none bred (although 1999 was breeding year). Although the routes chosen during spring migration were closely similar; none of the tagged birds migrated together. On average the geese used 16 flights to reach their summer destinations on Taymyr. The longest uninterrupted flights during the first half of the journey (Wadden Sea to Kanin) covered 1056 km (mean of seven adult males, range 768-1331), while the corresponding value for the second half of the migration (Kanin-Taymyr) was only 555 km (mean of six adult males). Only 7% of total time during spring migration was spent in active flight, as contrasted to c. 80% at long-term stopovers. Overall average travelling speed was 118 km/day (range 97-148). Including fattening prior to departure the rate of travel falls to 62 km/day (range 49-70), in keeping with theoretical predictions. Routes followed deviated from the great circle route, adding at least 700 km (16%) to the journey from Wadden Sea to Taymyr, and we conclude that the coastal route is chosen to facilitate feeding, drinking and resting en route instead of minimizing total flight distance.
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| 10. |
- Green, Martin, et al.
(författare)
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Do Arctic waders use adaptive wind drift?
- 2004
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Ingår i: Journal of Avian Biology. - : Wiley. - 0908-8857 .- 1600-048X. ; 35:4, s. 305-315
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Tidskriftsartikel (refereegranskat)abstract
- We analysed five data sets of night directions of migrating arctic waders ill relation to,winds, recorded by tracking radar and optical range finder, in order to find out if these birds compensate for wind drift, or allow themselves to be drifted by winds. Our purpose was to investigate whether arctic waders use adaptive wind drift strategies or not. The data sets were collected in Siberia (two sets) and Canada during post-breeding (autumn) migration, and in Mauritania and South Sweden during pre-breeding (spring) migration. Both significant drift and compensation effects were found in three of the data sets, Canada, Mauritania and South Sweden. Almost no compensation was found in birds departing in easterly directions from the Siberian tundra (complete drift), while no drift effect was found in birds departing in westerly directions (complete compensation). There were indications that at least some populations of waders may use an adaptive drift strategy consisting of drift at high altitude and/or in high wind speed combined with compensation at low altitude and/or in lower wind speeds, but support for this idea was rather weak and not consistent. Our results were instead more in accordance with the adaptive drift theory that predicts initial drift during the migratory journey, followed by compensation during later stages as the birds are approaching their destinations. Such a strategy implies that arctic waders, at least adult birds, have the capacity of true navigation. A comparison with earlier studies of migrating arctic waders from different parts of the world show that all results so far may be interpreted in accordance with this general adaptive drift strategy An element of non-adaptive drift can, however, not be completely ruled out.
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