| 1. |
- Alerstam, Thomas
(författare)
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Animal behaviour - The lobster navigators
- 2003
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 421:6918, s. 27-28
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Tidskriftsartikel (refereegranskat)abstract
- When experimentally displaced in geomagnetic space, spiny lobsters act as if to make their way home. This is a fascinating case of navigation by an invertebrate using a magnetic map sense.
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| 2. |
- Alerstam, Thomas, et al.
(författare)
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Bird migration speed
- 2003
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Ingår i: Avian migration. - 3540434089 ; , s. 253-267
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Abstract is not available
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| 3. |
- Alerstam, Thomas
(författare)
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Detours in bird migration
- 2001
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Ingår i: Journal of Theoretical Biology. - : Elsevier BV. - 1095-8541 .- 0022-5193. ; 209:3, s. 319-331
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Tidskriftsartikel (refereegranskat)abstract
- Bird migration routes often follow detours where passages across ecological barriers are reduced in extent. This occurs in spite of the fact that long barrier crossings are within the birds' potential flight range capacity. Long-distance flights are associated with extra energy costs for transport of the heavy fuel loads required. This paper explores how important the fuel transport costs, estimated on the basis of flight mechanics, map be to explain detours for birds migrating by flapping flight, Maximum detours in relation to expanse of the barrier are predicted for cases where birds travel along the detour by numerous short flights and small fuel reserves, divide the detour into a limited number of flight steps, and where a reduced barrier passage is included in the detour. The principles for determining the optimum route, often involving a shortcut across part of the barrier, are derived. Furthermore, the effects of differences in fuel deposition rates and in transport costs for the profitability of detours are briefly considered. An evaluation of a number of observed and potential detours in relation to the general predictions of maximum detours, indicates that reduction of fuel transport costs may well be a factor of widespread importance for the evolution of detours in bird migration at wide ecological barriers. (C) 2001 Academic Press.
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| 4. |
- Alerstam, Thomas
(författare)
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Evaluation of long-distance orientation in birds on the basis of migration routes recorded by radar and satellite tracking
- 2001
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Ingår i: Journal of Navigation. - 0373-4633. ; 54:3, s. 393-403
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Tidskriftsartikel (refereegranskat)abstract
- Predicted flight trajectories differ depending on which orientation cues are used by migrating birds. Results from radar and satellite tracking of migrating birds can be used to test which of the predicted trajectories shows the best fit with observed flight routes, supporting the use of the associated orientation mechanism. Radar studies of bird migration at the Northeast Passage and the Northwest Passage support the occurrence of migration along sun-compass routes in these polar regions. In contrast, satellite tracking of Brent geese (Branta bernicla) migrating from Iceland across Greenland and from Northwest Europe to Siberia show routes that conform most closely with geographic loxodromes, but which are also profoundly influenced by large-scale topography. These evaluations are discussed in relation to the adaptive values of different routes in different parts of the world. Sun compass routes are favourable mainly for east-west migration at high latitudes. For east-west migration at mid and high latitudes magnetic loxodromes are more favourable than geographic loxodromes in certain regions while the reverse holds in other regions. The geometry of migration routes, as recorded by radar and satellite tracking, may be important for understanding the evolution of the complexity of birds' orientation systems, and for providing clues about the orientation mechanisms guiding the birds on their global journeys.
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| 5. |
- Alerstam, Thomas, et al.
(författare)
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Long-distance migration: evolution and determinants
- 2003
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Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 103:2, s. 247-260
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Tidskriftsartikel (refereegranskat)abstract
- Long distance migration has evolved in many organisms moving through different media and using various modes of locomotion and transport. Migration continues to evolve or become suppressed as shown by ongoing dynamic and rapid changes of migration patterns. This great evolutionary flexibility may seem surprising for such a complex attribute as migration. Even if migration in most cases has evolved basically as a strategy to maximise fitness in a seasonal environment, its occurrence and extent depend on a multitude of factors. We give a brief overview of different factors (e.g. physical, geographical, historical, ecological) likely to facilitate and/or constrain the evolution of long distance migration and discuss how they are likely to affect migration. The basic driving forces for migration are ecological and biogeographic factors like seasonality, spatiotemporal distributions of resources, habitats, predation and competition. The benefit of increased resource availability will be balanced by costs associated with the migratory process in terms of time (incl. losses of prior occupancy advantages), energy and mortality (incl. increased exposure to parasites). Furthermore, migration requires genetic instructions (allowing substantial room for learning in some of the traits) about timing, duration and distance of migration as well as about behavioural and physiological adaptations (fuelling, organ flexibility, locomotion, use of environmental transport etc) and control of orientation and navigation. To what degree these costs and requirements put constraints on migration often depends on body size according to different scaling relationships. From this expos it is clear that research on migration warrants a multitude of techniques and approaches for a complete as possible understanding of a very complex evolutionary syndrome. In addition, we also present examples of migratory distances in a variety of taxons. In recent years new techniques, especially satellite radio telemetry, provide new information of unprecedented accuracy about journeys of individual animals, allowing re-evaluation of migration, locomotion and navigation theories.
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| 6. |
- 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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| 7. |
- Bäckman, Johan, et al.
(författare)
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Confronting the winds: orientation and flight behaviour of roosting swifts, Apus apus
- 2001
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Ingår i: Royal Society of London. Proceedings B. Biological Sciences. - : The Royal Society. - 1471-2954. ; 268:1471, s. 1081-1087
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Tidskriftsartikel (refereegranskat)abstract
- Swifts, Apus apus, spend the night aloft and this offers an opportunity to test the degree of adaptability of bird orientation and flight to different ecological situations. We predicted the swifts' behaviour by assuming that they are adapted to minimize energy expenditure during the nocturnal flight and during a compensatory homing flight if they become displaced by wind. We tested the predictions by recording the swifts' altitudes, speeds and directions under different wind conditions with tracking radar; we found an agreement between predictions and observations for orientation behaviour, but not for altitude and speed regulation. The swifts orientated consistently into the head wind, with angular concentration increasing with increasing wind speed. However, contrary to our predictions, they did not select altitudes with slow or moderate winds, nor did they increase their airspeed distinctly when flying into strong head winds. A possible explanation is that their head-wind orientation is sufficient to keep nocturnal displacement from their home area within tolerable limits, leaving flight altitude to be determined by other factors (correlated with temperature), and airspeed to show only a marginal increase in strong winds. The swifts were often moving 'backwards: heading straight into the wind but being overpowered by wind speeds exceeding their airspeed. The regular occurrence of such flights is probably uniquely associated with the swifts' remarkable habit of roosting on the wing.
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| 8. |
- Bäckman, Johan, et al.
(författare)
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Harmonic oscillatory orientation relative to the wind in nocturnal roosting flights of the swift Apus apus.
- 2002
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Ingår i: Journal of Experimental Biology. - 1477-9145. ; 205:Pt 7, s. 905-910
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Tidskriftsartikel (refereegranskat)abstract
- Swifts regularly spend the night flying at high altitude. From previous studies based on tracking radar observations, we know that they stay airborne during the night and prefer to orient themselves into the wind direction with an increased angular concentration with increasing wind speed. In this study, we investigated the orientation relative to the wind of individual swifts by frequency (discrete Fourier transform) and autocorrelation analysis based on time series (10s intervals) of the angle between the swifts' heading and the wind direction for radar trackings of long duration (9-60 min). The swifts often showed a significant harmonic oscillation of their heading direction relative to the wind, with a frequency mostly in the range 1-17 mHz, corresponding to cycle periods of 1-16 min. The swifts also sometimes performed circling flights at low wind speeds. Wind speed ranged from 1.3 to 14.8 m s(-1), and we expected to find different patterns of orientation at different wind speeds, assuming that the swifts adapt their orientation to avoid substantial displacement during their nocturnal flights. However, oscillatory orientation was found at all wind speeds with variable frequencies/periods that did not show any consistent relationship with wind speed. It remains to be shown whether cyclic heading changes are a regular feature of bird orientation.
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| 9. |
- Bäckman, Johan, et al.
(författare)
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Orientation scatter of free-flying nocturnal passerine migrants: components and causes
- 2003
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Ingår i: Animal Behaviour. - : Elsevier BV. - 1095-8282 .- 0003-3472. ; 65:5, s. 987-996
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the variation in concentration of orientation among nocturnally migrating passerine birds. Using tracking radar, we recorded flight tracks of birds during spring and autumn migration and, with the aid of concurrent wind recordings, we calculated heading directions. The concentrations of track and heading directions were compared between seasons and also between different categories of migrants that were defined by flight speed and wing beat frequency. Wind drift was a dominant cause of the large scatter of track directions, especially for autumn migration. When wind effects were compensated for, we found only small differences in the concentration of heading directions between different categories of migrants. This shows that between-group variation is not a major source of the overall variation in orientation when groups are distinguished on the basis of airspeed and wing beat frequency. Although the total concentration of heading directions was almost exactly the same for spring and autumn migrants, there was an element of partial compensation for wind drift in spring but not in autumn. When we removed the effect of this compensatory behaviour by considering situations with low wind speeds, the concentration of headings during spring tended to exceed that during the autumn. This suggests a more accurate orientation of the birds during spring than in autumn, when a large proportion consists of naive migrants on their first migratory journeys. The high concentration of heading directions of free-flying migrants are in clear contrast to the widely scattered distributions generally observed in orientation experiments with caged birds.
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| 10. |
- 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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