| 1. |
- Alerstam, Thomas, et al.
(author)
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A polar system of intercontinental bird migration
- 2007
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In: Royal Society of London. Proceedings B. Biological Sciences. - : The Royal Society. - 1471-2954. ; 274:1625, s. 2523-2530
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Journal article (peer-reviewed)abstract
- Studies of birdmigration in the Beringia region of Alaska and eastern Siberia are of special interest for revealing the importance of bird migration between Eurasia and North America, for evaluating orientation principles used by the birds at polar latitudes and for understanding the evolutionary implications of intercontinental migratory connectivity among birds as well as their parasites. We used tracking radar placed onboard the ice-breaker Oden to register bird migratory flights from 30 July to 19 August 2005 and we encountered extensive birdmigration in the whole Beringia range from latitude 64 degrees N in Bering Strait up to latitude 75 degrees N far north of Wrangel Island, with eastward flights making up 79% of all track directions. The results from Beringia were used in combination with radar studies from the Arctic Ocean north of Siberia and in the Beaufort Sea to make a reconstruction of a major Siberian-American birdmigration system in a wide Arctic sector between longitudes 1108 E and 130 degrees W, spanning one-third of the entire circumpolar circle. This system was estimated to involve more than 2 million birds, mainly shorebirds, terns and skuas, flying across the Arctic Ocean at mean altitudes exceeding 1 km (maximum altitudes 3-5 km). Great circle orientation provided a significantly better fit with observed flight directions at 20 different sites and areas than constant geographical compass orientation. The long flights over the sea spanned 40-80 degrees of longitude, corresponding to distances and durations of 1400-2600 km and 26-48 hours, respectively. The birds continued from this eastward migration system over the Arctic Ocean into several different flyway systems at the American continents and the Pacific Ocean. Minimization of distances between tundra breeding sectors and northerly stopover sites, in combination with the Beringia glacial refugium and colonization history, seemed to be important for the evolution of this major polar bird migration system.
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| 2. |
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| 3. |
- Alerstam, Thomas, et al.
(author)
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Great-Circle Migration Of Arctic Passerines
- 2008
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In: The Auk. - : Oxford University Press (OUP). - 0004-8038 .- 1938-4254. ; 125:4, s. 831-838
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Journal article (peer-reviewed)abstract
- Birds can save distance and time on their migratory journeys by following great circles rather than rhumblines, but great-circle routes require more complex orientation with changing courses. Flight directions at different places along the route and in relation to the destination can be used to test whether birds migrate along great circles or rhumblines. Such data have indicated great-circle migration among shorebirds at high latitudes, but no critical tests have been made for passerines. Using tracking radar on board the icebreaker Oden in August 2005, we recorded westerly flight directions of passerine migrants over the Chukchi Sea. The main sector of migratory directions was 237-311 degrees centered oil a mean heading direction of 274 degrees. The most likely species to participate in this westward trans-Beringia migration, mainly departing from Alaska, were Eastern Yellow Wagtail (Motacilla Ischutschensis), Arctic Warbler (Phylloscopus borealis kennicotti), Northern Wheatear (Oenanthe oenanthe), and Bluethroat (Luscinia svecica); all except the Bluethroat were recorded from the ship. Observed flight directions agreed with predicted great-circle courses but not with rhumbline courses for three of these four species with winter quarters in Southeast Asia; no definite conclusion could be drawn for the Northern Wheatear (wintering in East Africa). These results support great-circle migration among passerines traveling between Alaska and Old World winter quarters, though the long-distance precision and orientation mechanisms are Still unknown. The relative importance of different evolutionary causes-such as circumvention of geographic barriers, retracing of ancient colonization ways, or distance reduction by great-circle migration-to complex bird migration routes with changing courses remains to be understood. Received 24 August 2007, accepted 6 March 2008.
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| 4. |
- Alerstam, Thomas, et al.
(author)
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Hypotheses and tracking results about the longest migration : The case of the arctic tern
- 2019
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In: Ecology and Evolution. - : Wiley. - 2045-7758. ; 9:17, s. 9511-9531
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Journal article (peer-reviewed)abstract
- The arctic tern Sterna paradisaea completes the longest known annual return migration on Earth, traveling between breeding sites in the northern arctic and temperate regions and survival/molt areas in the Antarctic pack-ice zone. Salomonsen (1967, Biologiske Meddelelser, Copenhagen Danske Videnskabernes Selskab, 24, 1) put forward a hypothetical comprehensive interpretation of this global migration pattern, suggesting food distribution, wind patterns, sea ice distribution, and molt habits as key ecological and evolutionary determinants. We used light-level geolocators to record 12 annual journeys by eight individuals of arctic terns breeding in the Baltic Sea. Migration cycles were evaluated in light of Salomonsen's hypotheses and compared with results from geolocator studies of arctic tern populations from Greenland, Netherlands, and Alaska. The Baltic terns completed a 50,000 km annual migration circuit, exploiting ocean regions of high productivity in the North Atlantic, Benguela Current, and the Indian Ocean between southern Africa and Australia (sometimes including the Tasman Sea). They arrived about 1 November in the Antarctic zone at far easterly longitudes (in one case even at the Ross Sea) subsequently moving westward across 120–220 degrees of longitude toward the Weddell Sea region. They departed from here in mid-March on a fast spring migration up the Atlantic Ocean. The geolocator data revealed unexpected segregation in time and space between tern populations in the same flyway. Terns from the Baltic and Netherlands traveled earlier and to significantly more easterly longitudes in the Indian Ocean and Antarctic zone than terns from Greenland. We suggest an adaptive explanation for this pattern. The global migration system of the arctic tern offers an extraordinary possibility to understand adaptive values and constraints in complex pelagic life cycles, as determined by environmental conditions (marine productivity, wind patterns, low-pressure trajectories, pack-ice distribution), inherent factors (flight performance, molt, flocking), and effects of predation/piracy and competition.
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| 5. |
- Bonaldi, Carlotta, et al.
(author)
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Recurrence, fidelity and proximity to previously visited sites throughout the annual cycle in a trans-Saharan migrant, the common cuckoo
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In: Journal of Avian Biology. - 0908-8857.
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Journal article (peer-reviewed)abstract
- Most migratory birds return every year to the same breeding sites and some species show a similarly high fidelity to wintering grounds as well. Fidelity to stopover sites during migration has been much less studied and is usually found to be lower. Here, we investigate site fidelity and distance to previously visited sites throughout the annual cycle in the common cuckoo, a nocturnal trans-Saharan migrant, based on satellite-tracking data from repeated annual migrations of thirteen adult males. All birds (100%) returned to the same breeding grounds, with a median shortest distance of only 1 km from the locations in previous year. This was in strong contrast to a much lower and much less precise site fidelity at non-breeding sites during the annual cycle: In only 18% of the possible cases in all non-breeding regions combined, did the cuckoos return to within 50 km of a previously visited non-breeding site, with no significant differences among the main staging regions (Europe in autumn, Sahel in autumn, wintering in Central Africa, West Africa in spring, Europe in spring). The shortest distance to a previously visited non-breeding site differed among the staging regions with median shortest distances for the longest stopovers of 131 km [2;1223] (median [min;max]) in Europe, 207 km [1;2222] in Sahel in autumn and 110 km [0;628] in Central Africa. The distance to a previously visited staging site decreased with the time spent at the stopover in a previous year. Understanding the drivers of recurrence and site selection in migratory birds are important for guiding conservation efforts in this group but further studies are needed to establish whether the patterns observed in cuckoos are general among terrestrial migrants with continuous distribution of habitat.
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| 6. |
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| 7. |
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| 8. |
- Hedenström, Anders, et al.
(author)
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Radar Observations of Arctic Bird Migration in the Beringia Region
- 2009
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In: Arctic. - 0004-0843. ; 62:1, s. 25-37
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Journal article (peer-reviewed)abstract
- Bird migration was recorded by tracking radar and visual observations in the Beringia region. The data were subdivided into seven areas extending from north of Wrangel Island southeastward toward the Bering Strait and then northwestward off the coast of Alaska to Point Barrow. The studies, which took place during a ship-based expedition between 30 July and 19 August 2005, recorded a total of 557 tracks (average duration 120 seconds) of bird flocks or individuals on post-breeding migration. The dominant eastward-flying flocks were likely composed of shorebirds on their way from breeding areas in central or eastern Siberia to intermediate stopovers and final destinations in North and South America. The courses were more southerly into the Bering Strait, possibly because of topographical influence. At two areas, the Chukchi Sea and Koluchinskaya Bay, there was also a westward component of migrants. At the Chukchi Sea these were almost certainly passerine birds migrating from Alaska to wintering areas in Asia and Africa, while at Koluchinskaya Bay, king ciders on molt migration could represent an important part of the westward component. The overall mean altitude of flights was 1157 m, and flight altitude was positively correlated with latitude. The mean ground speed was 15.9 m/s and the mean airspeed was 14.1 m/s, indicating that on average the birds were experiencing a small tail wind component. The airspeed was a function of the tail wind component and the vertical speed; altitude and the side wind component did not contribute significantly to variation in airspeed in this data set. Comparing these results with similar data obtained from Siberia and Canada, we concluded that Beringia is a migration hotspot where intense bird migration crosses between Asia and Alaska in both directions.
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| 9. |
- Iwajomo, Soladoye B., et al.
(author)
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Intra-African movements of the African cuckoo Cuculus gularis as revealed by satellite telemetry
- 2018
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In: Journal of Avian Biology. - : Wiley. - 0908-8857. ; 49:1
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Journal article (peer-reviewed)abstract
- Despite many bird species migrating regularly within the African continent, in response to rainfall and breeding opportunities, documented evidence of the spatiotemporal patterns of such movements is scarce. We use satellite telemetry to document the year round movement of an intra-African migrant breeding in the savannah zone of sub-Saharan Africa, the African cuckoo. After breeding in central Nigeria, the birds migrated to more forested sites in the Adamawa region of Cameroon (n = 2) and western Central African Republic (n = 1). Departure from the breeding ground coincided with deteriorating environmental conditions whereas arrival at the non-breeding sites matched period of increasing vegetation greenness. Migratory movements generally occurred during dark hours. In total, an average distance of 748 km in 66 d was covered during the post-breeding migration and 744 km in 27 d during return journey with considerable individual variation and with more stopover sites used during post-breeding migration. The diversity of migration routes followed suggests a relatively variable or flexible initial migration strategy, high individual route consistency as well as high fidelity for non-breeding grounds.
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| 10. |
- Klaassen, Raymond, et al.
(author)
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Flexibility in daily travel routines causes regional variation in bird migration speed
- 2008
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In: Behavioral Ecology and Sociobiology. - : Springer Science and Business Media LLC. - 1432-0762 .- 0340-5443. ; 62:9, s. 1427-1432
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Journal article (peer-reviewed)abstract
- We used novel Global Positioning System-based satellite telemetry to reconstruct daily time budgets on travelling days of a long-distance migrant, the Osprey Pandion haliaetus, to reveal how landscape affects migratory performance. We compared daily travel routines between the Ospreys' passage of Europe and the Sahara. In Europe, where feeding habitat is abundant, Ospreys fed both before-after flights and during interruptions, thus, combining migration with foraging. This resulted in a 2.7-h shorter daily flight period in Europe than in the Sahara. A calculated energy budget indicated that a 'fly-and-forage migration strategy' is favourable in Europe because associated benefits (energy intake) more than outweigh costs (reduced flight time). The much shorter flight time in Europe was the main explanation why Ospreys covered on average 78 km less distance on a travelling day in Europe than in the Sahara. In addition, there were regional differences in hourly flight speeds that are most probably the result of variation in thermal soaring conditions. We conclude that landscape properties have a profound effect on migration through regional variation in daily routines.
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| 11. |
- Klaassen, Raymond, et al.
(author)
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Geographical and temporal flexibility in the response to crosswinds by migrating raptors.
- 2011
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In: Proceedings of the Royal Society B: Biological Sciences. - : The Royal Society. - 1471-2954 .- 0962-8452. ; 278, s. 1339-1346
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Journal article (peer-reviewed)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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| 12. |
- Klaassen, Raymond, et al.
(author)
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Loop migration in adult marsh harriers Circus aeruginosus, as revealed by satellite telemetry
- 2010
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In: Journal of Avian Biology. - 0908-8857 .- 1600-048X. ; 41:2, s. 200-207
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Journal article (peer-reviewed)abstract
- Loop migration among birds is characterized by the spring route lying consistently west or east of the autumn route. The existence of loops has been explained by general wind conditions or seasonal differences in habitat distribution. Loop migration has predominantly been studied at the population level, for example by analysing ring recoveries. Here we study loop migration of individual marsh harriers Circus aeruginosus tracked by satellite telemetry. We show that despite a generally narrow migration corridor the harriers travelled in a distinct clockwise loop through Africa and southern Europe, following more westerly routes in spring than in autumn. We used the Normalized Difference Vegetation Index (NDVI) to identify potential feeding habitat in Africa. Suitable habitat seemed always more abundant along the western route, both in spring and autumn, and no important stopover site was found along the eastern route. Observed routes did thus not coincide with seasonal variation in habitat availability. However, favourable habitat might be more important during spring migration, when the crossing of the Sahara seems more challenging, and thus habitat availability might play an indirect role in the harriers' route choice. Grid-based wind data were used to reconstruct general wind patterns, and in qualitative agreement with the observed loop marsh harriers predominantly encountered westerly winds in Europe and easterly winds in Africa, both in autumn and in spring. By correlating tail- and crosswinds with forward and perpendicular movement rates, respectively, we show that marsh harriers are partially drifted by wind. Thus, we tentatively conclude that wind rather than habitat seems to have an overriding effect on the shape of the migration routes of marsh harriers. General wind conditions seem to play an important role also in the evolution of narrow migratory loops as demonstrated for individual marsh harriers.
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| 13. |
- Klaassen, Raymond, et al.
(author)
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When and where does mortality occur in migratory birds? Direct evidence from long-term satellite tracking of raptors.
- 2014
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In: Journal of Animal Ecology. - : Wiley. - 1365-2656 .- 0021-8790. ; 83:1, s. 176-184
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Journal article (peer-reviewed)abstract
- Information about when and where animals die is important to understand population regulation. In migratory animals, mortality might occur not only during the stationary periods (e.g. breeding and wintering) but also during the migration seasons. However, the relative importance of population limiting factors during different periods of the year remains poorly understood, and previous studies mainly relied on indirect evidence. Here, we provide direct evidence about when and where migrants die by identifying cases of confirmed and probable deaths in three species of long-distance migratory raptors tracked by satellite telemetry. We show that mortality rate was about six times higher during migration seasons than during stationary periods. However, total mortality was surprisingly similar between periods, which can be explained by the fact that risky migration periods are shorter than safer stationary periods. Nevertheless, more than half of the annual mortality occurred during migration. We also found spatiotemporal patterns in mortality: spring mortality occurred mainly in Africa in association with the crossing of the Sahara desert, while most mortality during autumn took place in Europe. Our results strongly suggest that events during the migration seasons have an important impact on the population dynamics of long-distance migrants. We speculate that mortality during spring migration may account for short-term annual variation in survival and population sizes, while mortality during autumn migration may be more important for long-term population regulation (through density-dependent effects).
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| 14. |
- Mellone, Ugo, et al.
(author)
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Interspecific Comparison of the Performance of Soaring Migrants in Relation to Morphology, Meteorological Conditions and Migration Strategies
- 2012
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In: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 7:7
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Journal article (peer-reviewed)abstract
- Background: Performance of migrating birds can be affected by a number of intrinsic and extrinsic factors like morphology, meteorological conditions and migration strategies. We compared travel speeds of four raptor species during their crossing of the Sahara desert. Focusing the analyses on this region allows us to compare different species under equivalent conditions in order to disentangle which factors affect migratory performance. Methodology/Principal Finding: We tracked raptors using GPS satellite transmitters from Sweden, Spain and Italy, and evaluated their migratory performance at both an hourly and a daily scale. Hourly data (flight speed and altitude for intervals of two hours) were analyzed in relation to time of day, species and season, and daily data (distance between roosting sites) in relation to species, season, day length and tailwind support. Conclusions/Significance: Despite a clear variation in morphology, interspecific differences were generally very small, and did only arise in spring, with long-distance migrants (>5000 km: osprey and Western marsh-harrier) being faster than species that migrate shorter distances (Egyptian vulture and short-toed eagle). Our results suggest that the most important factor explaining hourly variation in flight speed is time of day, while at a daily scale, tailwind support is the most important factor explaining variation in daily distance, raising new questions about the consequences of possible future changes in worldwide wind patterns.
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| 15. |
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| 16. |
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| 17. |
- Pedersen, Lykke, et al.
(author)
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Sex-specific difference in migration schedule as a precursor of protandry in a long-distance migratory bird
- 2019
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In: Science of Nature. - : Springer Science and Business Media LLC. - 0028-1042 .- 1432-1904. ; 106:7-8
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Journal article (peer-reviewed)abstract
- Protandry, the earlier arrival of males at the breeding grounds relative to females, is common in migratory birds. However, due to difficulties in following individual birds on migration, we still lack knowledge about the spatiotemporal origin of protandry during the annual cycle, impeding our understanding of the proximate drivers of this phenomenon. Here, we use full annual cycle tracking data of red-backed shrikes Lanius collurio to investigate the occurrence of sex-related differences in migratory pattern, which could be viewed as precursors (proximate causes) to protandry. We find protandry with males arriving an estimated 8.3 days (SE = 4.1) earlier at the breeding area than females. Furthermore, we find that, averaged across all departure and arrival events throughout the annual cycle, males migrate an estimated 5.3 days earlier than females during spring compared to 0.01 days in autumn. Event-wise estimates suggest that a divergence between male and female migratory schedules is initiated at departure from the main non-breeding area, thousands of kilometres from-, and several months prior to arrival at the breeding area. Duration of migration, flight speed during migration and spatial locations of stationary sites were similar between sexes. Our results reveal that protandry might arise from sex-differential migratory schedules emerging at the departure from the main non-breeding area in southern Africa and retained throughout spring migration, supporting the view that sex-differential selection pressure operates during spring migration rather than autumn migration.
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| 18. |
- Strandberg, Roine, et al.
(author)
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Bird observations in Mali
- 2007
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In: Malimbus. - 0331-3689. ; 29:2, s. 123-125
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Journal article (pop. science, debate, etc.)
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| 19. |
- Strandberg, Roine, et al.
(author)
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Complex timing of Marsh Harrier Circus aeruginosus migration due to pre- and post-migratory movements
- 2008
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In: Ardea. - 0373-2266. ; 96:2, s. 159-171
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Journal article (pop. science, debate, etc.)abstract
- We tracked three juvenile and 14 adult Marsh Harriers Circus aeruginosus from southern Sweden via satellite to investigate migration strategies. Four individuals were tracked for at least two years. All three juveniles and four of the adults made west-oriented pre-migratory movements well before the onset of autumn migration, and trans-Saharan migrants visited post-migratory stopover areas in tropical Africa. By these movements, the harriers presumably exploit short-term regional variation in food abundance. Autumn and spring migration occurred in a relatively narrow corridor, without distinct differences between sexes in timing, speed, distance, and duration of migration, except that females tended to migrate faster in spring than did males. Juveniles migrated shorter distances than adults, and migration speeds were lower. Spring migration was similar to autumn migration in terms of speed and duration. Juveniles did not cross the Sahara Desert and three birds, one female and two juveniles, wintered in Europe, which is in accordance with a recent increase in the number of (juvenile) Marsh Harriers wintering in northwestern Europe. All birds that crossed the Sahara wintered in tropical West Africa. Harriers showed site fidelity to breeding, wintering and stopover areas. The overall migration speed of Marsh Harriers was similar to that of Ospreys Pandion haliaetus and Honey Buzzards Pernis apivorus, two other trans-Saharan migrants. Ospreys use fly-and-forage migration to promote resulting speed, whereas Honey Buzzards are particularly apt to exploit thermal soaring. How Marsh Harriers balance foraging versus travelling to accomplish their rapid migration speeds remains to be resolved.
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| 20. |
- Strandberg, Roine, et al.
(author)
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Converging migration routes of Eurasian hobbies Falco subbuteo crossing the African equatorial rain forest.
- 2009
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In: Royal Society of London. Proceedings B. Biological Sciences. - : The Royal Society. - 1471-2954 .- 0962-8452. ; 276:1657, s. 727-733
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Journal article (peer-reviewed)abstract
- Autumn migration of adult Eurasian hobbies Falco subbuteo from Europe to southern Africa was recorded by satellite telemetry and observed routes were compared with randomly simulated routes. Two non-random features of observed routes were revealed: (i) shifts to more westerly longitudes than straight paths to destinations and (ii) strong route convergence towards a restricted area close to the equator (1 degrees S, 15 degrees E). The birds migrated south or southwest to approximately 10 degrees N, where they changed to south-easterly courses. The maximal spread between routes at 10 degrees N (2134km) rapidly decreased to a minimum (67km) close to the equator. We found a striking relationship between the route convergence and the distribution of continuous rainforest, suggesting that hobbies minimize flight distance across the forest, concentrating in a corridor where habitat may be more suitable for travelling and foraging. With rainforest forming a possible ecological barrier, many migrants may cross the equator either at 15 degrees E, similar to the hobbies, or at 30-40 degrees E, east of the rainforest where large-scale migration is well documented. Much remains to be understood about the role of the rainforest for the evolution and future of the trans-equatorial Palaearctic-African bird migration systems.
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| 21. |
- Strandberg, Roine, et al.
(author)
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Daily travel schedules of adult Eurasian Hobbies Falco subbuteo - variability in flight hours and migration speed along the route
- 2009
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In: Ardea. - 0373-2266. ; 97:3, s. 287-295
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Journal article (peer-reviewed)abstract
- We analysed satellite tracking data to reveal the daily travel schedules of Hobbies Falco subbuteo migrating between northern Europe and southern Africa. By comparing movements during short-time intervals of 1-8 h at different times of the day between the three different regions Europe, Sahara Desert and tropical Africa, we found significant higher hourly speeds in the Sahara compared to the other two regions. The migration started early in the morning and continued throughout the day, resulting in daily travel time exceeding that of typical thermal soaring migrants. Due to fast hourly speeds in combination with the long travel days during Sahara crossings, the Hobbies exceeded daily travel distances recorded for soaring migrants. In Europe and tropical Africa, the speed was highly variable during the day, and lower flight speeds, especially during afternoons, suggest a fly-and-forage strategy, Our predictions about regular occurrence of nocturnal flight especially across geographical barriers as the desert were not fulfilled. In the Sahara, the Hobbies restricted their movement to diurnal migration. Nevertheless, 10% of the flight segments in tropical Africa were partly or completely during night hours and Hobbies often started their daily flight before or at sunrise. We attribute the special characteristics of the daily travel schedules of Hobbies primarily to their use of a fly-and-forage strategy, possibly in combination with preparedness for exploiting thermals during the daily thermal time window. Further studies are needed to understand why Hobbies do not increase daily travelling hours to include regular nocturnal flight in the Sahara Desert. We suggest that the daily travel schedules of the Hobby, which were distinctly different from those of other diurnal migrants like large raptors (which mainly exploit thermal soaring migration) or pipits, wagtails, finches and pigeons (which mainly travel during the morning hours) may be typical for bird species that primarily use a fly-and-forage migration strategy.
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| 22. |
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| 23. |
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| 24. |
- Strandberg, Roine, et al.
(author)
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How hazardous is the Sahara Desert crossing for migratory birds? Indications from satellite tracking of raptors.
- 2010
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In: Biology letters. - : The Royal Society. - 1744-9561 .- 1744-957X. ; 6, s. 297-300
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Journal article (peer-reviewed)abstract
- We investigated the risk associated with crossing the Sahara Desert for migrating birds by evaluating more than 90 journeys across this desert by four species of raptors (osprey Pandion haliaetus, honey buzzard Pernis apivorus, marsh harrier Circus aeruginosus and Eurasian hobby Falco subbuteo) recorded by satellite telemetry. Forty per cent of the crossings included events of aberrant behaviours, such as abrupt course changes, slow travel speeds, interruptions, aborted crossings followed by retreats from the desert and failed crossings due to death, indicating difficulties for the migrants. The mortality during the Sahara crossing was 31 per cent per crossing attempt for juveniles (first autumn migration), compared with only 2 per cent for adults (autumn and spring combined). Mortality associated with the Sahara passage made up a substantial fraction (up to about half for juveniles) of the total annual mortality, demonstrating that this passage has a profound influence on survival and fitness of migrants. Aberrant behaviours resulted in late arrival at the breeding grounds and an increased probability of breeding failure (carry-over effects). This study also demonstrates that satellite tracking can be a powerful method to reveal when and where birds are exposed to enhanced risk and mortality during their annual cycles.
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| 25. |
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| 26. |
- Strandberg, Roine
(author)
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Migration strategies of raptors – spatio-temporal adaptations and constraints in travelling and foraging
- 2008
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Doctoral thesis (other academic/artistic)abstract
- My dissertation is about bird migration and addresses questions about how raptors adapt to the fluctuating environments during the transition seasons between breeding and wintering. The migration is highly affected by local prey abundance, foraging strategies, weather conditions and landscape patterns along the migration routes as well as navigation and orientation mechanisms and cues. Interesting findings in my studies were how raptors can mix foraging and active migration during their travels. A strategy of fly-and-forage migration is favourable for birds that hunt on their wings, able to combine foraging with covering travel distance. Fly-and-forage migration is favourable for Ospreys in Europe because benefits (energy intake) more than outweigh costs (reduced flight time). Among different species and populations of migratory raptors, duration of migration increased approximately in proportion to the square root of total migration distance. This reflects a shifting balance in the selection for speed and duration depending on distance of migration. The general wind patterns along the migration routes with dominating winds from the east over the Saharan Desert and from the west over Europe, mediate migration in a clockwise loop, where Marsh Harriers could increase flight speed across the desert with tailwinds in autumn and by avoiding headwinds in spring. In addition to seas and deserts, we found the equatorial rain forest as a potential ecological barrier for migrating birds. A striking relationship of route convergence with the distribution of continuous rain forest suggests minimized crossings of this habitat by Hobbies. The migration journeys by raptors across the Sahara Desert showed that 37% of all crossings included events of aberrant behaviour indicating difficulties or hazards. Mortality associated with the Sahara passages contributed to about half of the total annual mortality among juveniles as well as adults, demonstrating that this passage has a profound influence on survival and fitness of the migrants. Comparisons of satellite tracking and ring recoveries of raptors revealed agreement in the geographical distribution but differences in timing of migration. Tracks showed a faster progress for long-distance migrants, which probably related to more detailed information from tracking in Africa, difficulties in judging time of death for recovered birds and an overrepresentation of recoveries in Europe. An important and challenging goal for future studies of raptor migration will be to track juveniles from their first journeys until they are migrating as experienced adults. This would give a better understanding of how migration strategies are developed and to what degree they are inherited or based on learning.
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| 27. |
- Strandberg, Roine, et al.
(author)
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Movements of immature European Honey Buzzards Pernis apivorus in tropical Africa
- 2012
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In: Ardea. - : Netherlands Ornithologists' Union. - 0373-2266. ; 100:2, s. 157-162
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Journal article (peer-reviewed)abstract
- Strandberg R., Hake M., Klaassen R.H.G. & Alerstam T. 2012. Movements of immature European Honey Buzzards Pernis apivorus in tropical Africa. Ardea 100: 157-162. Immature European Honey Buzzards Pernis apivorus are believed to remain in tropical Africa during the first years of their lives. We studied their movements during this period with the aid of satellite telemetry. After crossing the Sahara Desert on autumn migration, all six tracked young buzzards stopped at relatively northerly latitudes, between 9.9-13.6 degrees N. Of the five individuals that continued transmitting, four made south-directed movements, mainly in November, to areas located further south or east within latitudes 1.7-9.8 degrees N. Three young buzzards were tracked for more than three months in tropical Africa, and these individuals continued to perform extensive movements within the tropics throughout the tracking period. They travelled between 2,430 and 3,990 km (minimum distances) during 13 to 14 months, in which they visited several sites. In contrast, adult birds migrate directly to their wintering sites where they remain stationary within restricted territories. The mobile life of young Honey Buzzards during the period prior to their first northbound migration may be associated with responses to seasonal weather changes in the tropics and prospecting behaviour. These movements may also reflect intraspecific competition which might be catalyzed by forest degradation and fragmentation.
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| 28. |
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| 29. |
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| 30. |
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| 31. |
- Strandberg, Roine, et al.
(author)
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Spatio-temporal distribution of migrating raptors: a comparison of ringing and satellite tracking
- 2009
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In: Journal of Avian Biology. - 0908-8857. ; 40:5, s. 500-510
-
Journal article (peer-reviewed)abstract
- We describe the migration performance of three long-distance migrating raptors, osprey Pandion haliaetus, honey buzzard Pernis apivorus and marsh harrier Circus aeruginosus, and one short-distance migrating raptor, common buzzard Buteo buteo based on Swedish ringing recoveries and satellite telemetry, respectively. Tracking by satellite can provide detailed information about the exact timing of migration, migration speed, migration directions, stopover sites, and detours, thereby overcoming many of the potential biases found in ring recoveries. Comparison of the results from these two methods revealed agreement in the geographical distribution of the studied Swedish raptor populations during autumn migration and the winter period. Satellite tracking, nevertheless, provided much more detailed information in Africa and revealed significantly faster migration progress than indicated by ring recoveries. The implications of our findings for interpretation of migratory connectivity and the understanding of migration are discussed.
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| 32. |
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| 33. |
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| 34. |
- Strandberg, Roine, et al.
(author)
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The strategy of fly-and-forage migration, illustrated for the osprey (Pandion haliaetus)
- 2007
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In: Behavioral Ecology and Sociobiology. - : Springer Science and Business Media LLC. - 1432-0762 .- 0340-5443. ; 61:12, s. 1865-1875
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Journal article (peer-reviewed)abstract
- Migrating birds often alternate between flight steps, when distance is covered and energy consumed, and stopover periods, when energy reserves are restored. An alternative strategy is fly-and-forage migration, useful mainly for birds that hunt or locate their prey in flight, and thus, enables birds to combine foraging with covering migration distance. The favourability of this strategy in comparison with the traditional stopover strategy depends on costs of reduced effective travel speed and benefits of offsetting energy consumption during migration flights. Evaluating these cost-benefit effects, we predict that fly-and-forage migration is favourable under many conditions (increasing total migration speed), both as a pure strategy and in combination with stopover behaviour. We used the osprey (Pandion haliaetus) as test case for investigating the importance of this strategy during spring and autumn migration at a lake in southern Sweden. The majority, 78%, of passing ospreys behaved according to the fly-and-forage migration strategy by deviating from their migratory track to visit or forage at the lake, while 12% migrated past the lake without response, and 10% made stopovers at the lake. Foraging success of passing ospreys was almost as good as for birds on stopover. Timing of foraging demonstrated that the birds adopted a genuine fly-and-forage strategy rather than intensified foraging before and after the daily travelling period. We predict that fly-and-forage migration is widely used and important among many species besides the osprey, and the exploration of its occurrence and consequences will be a challenging task in the field of optimal migration.
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| 35. |
- Strandberg, Roine, et al.
(author)
-
Wind-dependent foraging flight in the Osprey Pandion haliaetus
- 2006
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In: Ornis Svecica. - 1102-6812. ; 16:3, s. 150-163
-
Journal article (peer-reviewed)abstract
- We studied the foraging technique of Ospreys Pandion haliaetus during different wind speed conditions at Lake Hammarsjon, Sweden in autumn 2003. Different fishing techniques were used with a shift in relation to wind speed: (1) without hovering, (2) hovering with pure flapping flight, (3) hovering with flapping flight and gliding into the wind, and (4) hovering with pure gliding. The results supported our predictions that hovering is constrained at low wind speeds and gliding restricted to wind speeds exceeding 7 m/s. Mixing flapping and gliding flight when hovering may be done as a trade-off between increased fishing efficiency associated with flapping flight and energy-saving combined with gain in total hovering time associated with gliding intervals. The relationship between hovering time and wind speed differed significantly between males and females. At wind speeds up to about 3.0 m/s, the hovering time increased more steeply with increasing wind speed for males than for females. In contrast, hovering time was shorter for males than for females at high wind speeds. The juveniles showed a lower mean, smaller scatter, and less increase in hovering time along the wind speed gradient.
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| 36. |
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| 37. |
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| 38. |
- Thorup, K, et al.
(author)
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Do migratory flight paths of raptors follow constant geographical or geomagnetic courses?
- 2006
-
In: Animal Behaviour. - : Elsevier BV. - 1095-8282 .- 0003-3472. ; 72:4, s. 875-880
-
Journal article (peer-reviewed)abstract
- We tested whether routes of raptors migrating over areas with homogeneous topography follow constant geomagnetic courses more or less closely than constant geographical courses. We analysed the routes taken over land of 45 individual raptors tracked by satellite-based radiotelemetry: 25 peregrine falcons, Falco peregrinus, on autumn migration between North and South America, and seven honey buzzards, Pernis apivorus, and 13 ospreys, Pandion haliaetus, on autumn migration between Europe and Africa. Overall, migration directions showed a better agreement with constant geographical than constant geomagnetic courses. Tracks deviated significantly from constant geomagnetic courses, but were not significantly different from geographical courses. After we removed movements directed far from the mean direction, which may not be migratory movements, migration directions still showed a better agreement with constant geographical than constant geomagnetic courses, but the directions of honey buzzards and ospreys were not significantly different from constant geomagnetic courses either. That migration routes of raptors followed by satellite telemetry are in closer accordance with constant geographical compass courses than with constant geomagnetic compass courses may indicate that geographical (e.g. based on celestial cues) rather than magnetic compass mechanisms are of dominating importance for the birds' long-distance orientation. Published by Elsevier Ltd on behalf of The Association for the Study or Animal Behaviour.
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| 39. |
- Thorup, Kasper, et al.
(author)
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Resource tracking within and across continents in long-distance bird migrants
- 2017
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In: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 3:1
-
Journal article (peer-reviewed)abstract
- Migratory birds track seasonal resources across and between continents. We propose a general strategy of tracking the broad seasonal abundance of resources throughout the annual cycle in the longest-distance migrating land birds as an alternative to tracking a certain climatic niche or shorter-term resource surplus occurring, for example, during spring foliation. Whether and how this is possible for complex annual spatiotemporal schedules is not known. New tracking technology enables unprecedented spatial and temporal mapping of long-distance movement of birds. We show that three Palearctic-African species track vegetation greenness throughout their annual cycle, adjusting the timing and direction of migratory movements with seasonal changes in resource availability over Europe and Africa. Common cuckoos maximize the vegetation greenness, whereas red-backed shrikes and thrush nightingales track seasonal surplus in greenness. Our results demonstrate that the longest-distance migrants move between consecutive staging areas even within the wintering region in Africa to match seasonal variation in regional climate. End-of-century climate projections indicate that optimizing greenness would be possible but that vegetation surplus might be more difficult to track in the future.
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| 40. |
- Tottrup, A. P., et al.
(author)
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Drought in Africa Caused Delayed Arrival of European Songbirds
- 2012
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In: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 338:6112, s. 1307-1307
-
Journal article (peer-reviewed)abstract
- A severe drought in the Horn of Africa delayed the spring arrival in Europe of two migratory species.
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| 41. |
- Tottrup, Anders P., et al.
(author)
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The annual cycle of a trans-equatorial Eurasian-African passerine migrant: different spatio-temporal strategies for autumn and spring migration
- 2012
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In: Royal Society of London. Proceedings B. Biological Sciences. - : The Royal Society. - 1471-2954. ; 279:1730, s. 1008-1016
-
Journal article (peer-reviewed)abstract
- The small size of the billions of migrating songbirds commuting between temperate breeding sites and the tropics has long prevented the study of the largest part of their annual cycle outside the breeding grounds. Using light-level loggers (geolocators), we recorded the entire annual migratory cycle of the red-backed shrike Lanius collurio, a trans-equatorial Eurasian-African passerine migrant. We tested differences between autumn and spring migration for nine individuals. Duration of migration between breeding and winter sites was significantly longer in autumn (average 96 days) when compared with spring (63 days). This difference was explained by much longer staging periods during autumn (71 days) than spring (9 days). Between staging periods, the birds travelled faster during autumn (356 km d(-1)) than during spring (233 km d(-1)). All birds made a protracted stop (53 days) in Sahelian sub-Sahara on southbound migration. The birds performed a distinct loop migration (22 000 km) where spring distance, including a detour across the Arabian Peninsula, exceeded the autumn distance by 22 per cent. Geographical scatter between routes was particularly narrow in spring, with navigational convergence towards the crossing point from Africa to the Arabian Peninsula. Temporal variation between individuals was relatively constant, while different individuals tended to be consistently early or late at different departure/arrival occasions during the annual cycle. These results demonstrate the existence of fundamentally different spatio-temporal migration strategies used by the birds during autumn and spring migration, and that songbirds may rely on distinct staging areas for completion of their annual cycle, suggesting more sophisticated endogenous control mechanisms than merely clockand-compass guidance among terrestrial solitary migrants. After a century with metal-ringing, year-round tracking of long-distance migratory songbirds promises further insights into bird migration.
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| 42. |
- Vansteelant, Wouter M.G., et al.
(author)
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Western Marsh Harriers Circus aeruginosus from nearby breeding areas migrate along comparable loops, but on contrasting schedules in the West African–Eurasian flyway
- 2020
-
In: Journal of Ornithology. - : Springer Science and Business Media LLC. - 2193-7192 .- 2193-7206. ; 161:4, s. 953-965
-
Journal article (peer-reviewed)abstract
- Much of our knowledge about migratory behaviour comes from single-population tracking studies. Some such studies had a considerable impact on migration research at large. However, it is often unclear how representative such studies are for other populations, even of the same species. We compared migration corridors and schedules of GPS-tracked adult Western Marsh Harriers (Circus aeruginosus) from two nearby breeding areas within the West African–Eurasian flyway: the Low Countries (LC, N = 6) and southern Sweden (SW, N = 4). Assuming the migration patterns revealed by decade-old satellite-tracking of SW harriers are representative for the species, we expected LC harriers to make a narrow loop migration involving a western spring detour out of Africa, but according to an earlier schedule tuned to the earlier onset of spring in the Low Countries. In autumn, LC harriers migrated significantly further west than SW harriers all the way to their common non-breeding range. In spring, both groups detoured westward across the Sahara, as expected, and diverged towards their breeding areas after reaching mainland Europe. LC harriers migrated slightly earlier than SW harriers in autumn. However, LC harriers unexpectedly left their non-breeding sites up to a month before SW harriers, after which they made long stop-overs in northwest Africa. Late-departing SW harriers forewent these stop-overs, and thus caught up with LC harriers in northwest Africa, so that both groups reached their breeding areas simultaneously. While we anticipated strong overlap between LC and SW migration corridors in spring, we failed to anticipate the earlier and more variable spring departures of LC harriers. Early spring departures did not result in earlier arrivals by LC harriers. Instead, we suspect they departed early to escape faster deteriorating foraging conditions at their non-breeding sites. Such environmental modulation of migratory behaviour may complicate generalization of migration patterns in other birds.
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| 43. |
- Vardanis, Yannis, et al.
(author)
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Consistency in long-distance bird migration: Contrasting patterns in time and space for two raptors
- 2016
-
In: Animal Behaviour. - : Elsevier BV. - 0003-3472. ; 113, s. 177-187
-
Journal article (peer-reviewed)abstract
- As the evolutionary responses to environmental change depend on selection acting on individual differences,disentangling within- and between-individual variation becomes imperative. In animalmigration research, multiyear tracks are thus needed to estimate the individual consistency of phenotypictraits. Avian telemetry studies have recently provided the first evidence of individuality acrossspace and time in animal migration. Here, we compare repeatability patterns of routes and timing betweentwo migratory birds, the marsh harrier, Circus aeruginosus, and the osprey, Pandion haliaetus, asrecorded by satellite tracking. We found interspecific contrasts with low repeatability in timing andduration and a high repeatability in routes for ospreys, but the reverse pattern for marsh harriers. Thiswas mainly caused by (1) larger between-individual variation in routes for ospreys (broad-frontmigration) than for marsh harriers (corridor migration) and a higher degree of repeated use of the samestopover sites among ospreys, and (2) higher within-individual consistency of timing and durationamong marsh harriers, while individual ospreys were more flexible. Our findings suggest that individualityin space and time is not a shared trait complex among migrants, but may show adaptivevariation depending on the species' life history and ecology.
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| 44. |
- Vardanis, Yannis, et al.
(author)
-
Individuality in bird migration: routes and timing
- 2011
-
In: Biology letters. - : The Royal Society. - 1744-9561 .- 1744-957X. ; 7, s. 502-505
-
Journal article (peer-reviewed)abstract
- The exploration of animal migration has entered a new era with individual-based tracking during multiple years. Here, we investigated repeated migratory journeys of a long-distance migrating bird, the marsh harrier Circus aeruginosus, in order to analyse the variation within and between individuals with respect to routes and timing. We found that there was a stronger individual repeatability in time than in space. Thus, the annual timing of migration varied much less between repeated journeys of the same individual than between different individuals, while there was considerable variation in the routes of the same individual on repeated journeys. The overall contrast in repeatability between time and space was unexpected and may be owing to strong endogenous control of timing, while short-term variation in environmental conditions (weather and habitat) might promote route flexibility. The individual variation in migration routes indicates that the birds navigate mainly by other means than detailed route recapitulation based on landmark recognition.
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| 45. |
- Vega, Marta Lomas, et al.
(author)
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First-time migration in juvenile common cuckoos documented by satellite tracking
- 2016
-
In: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 11:12
-
Journal article (peer-reviewed)abstract
- Being an obligate parasite, juvenile common cuckoos Cuculus canorus are thought to reach their African wintering grounds from Palearctic breeding grounds without guidance from experienced conspecifics but this has not been documented. We used satellite tracking to study naïve migrating common cuckoos. Juvenile cuckoos left breeding sites in Finland moving slowly and less consistently directed than adult cuckoos. Migration of the juveniles (N = 5) was initiated later than adults (N = 20), was directed toward the southwest-significantly different from the initial southeast direction of adults-and included strikingly long Baltic Sea crossings (N = 3). After initial migration of juvenile cuckoos toward Poland, the migration direction changed and proceeded due south, directly toward the winter grounds, as revealed by a single tag transmitting until arrival in Northwest Angola where northern adult cuckoos regularly winter. Compared to adults, the juvenile travelled straighter and faster, potentially correcting for wind drift along the route. That both migration route and timing differed from adults indicates that juvenile cuckoos are able to reach proper wintering grounds independently, guided only by their innate migration programme.
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| 46. |
- Willemoes, Mikkel, et al.
(author)
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Narrow-Front Loop Migration in a Population of the Common Cuckoo Cuculus canorus, as Revealed by Satellite Telemetry.
- 2014
-
In: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9:1
-
Journal article (peer-reviewed)abstract
- Narrow migration corridors known in diurnal, social migrants such as raptors, storks and geese are thought to be caused by topographical leading line effects in combination with learning detailed routes across generations. Here, we document narrow-front migration in a nocturnal, solitary migrant, the common cuckoo Cuculus canorus, using satellite telemetry. We tracked the migration of adult cuckoos from the breeding grounds in southern Scandinavia (n = 8), to wintering sites in south-western Central Africa (n = 6) and back to the breeding grounds (n = 3). Migration patterns were very complex; in addition to the breeding and wintering sites, six different stopover sites were identified during the 16,000 km annual route that formed a large-scale clockwise loop. Despite this complexity, individuals showed surprisingly similar migration patterns, with very little variation between routes. We compared observed tracks with simulated routes based on vector orientation (with and without effects of barriers on orientation and survival). Observed distances between routes were often significantly smaller than expected if the routes were established on the basis of an innate vector orientation programme. Average distance between individuals in eastern Sahel after having migrated more than 5,000 km for example, was merely 164 km. This implies that more sophisticated inherent guiding mechanisms, possibly involving elements of intermediate goal area navigation or more elaborate external cues, are necessary to explain the complex narrow-front migration pattern observed for the cuckoos in this study.
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| 47. |
- Williams, Heather M., et al.
(author)
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Common Cuckoo home ranges are larger in the breeding season than in the non-breeding season and in regions of sparse forest cover
- 2016
-
In: Journal of Ornithology. - : Springer Science and Business Media LLC. - 2193-7192 .- 2193-7206. ; 157:2, s. 461-469
-
Journal article (peer-reviewed)abstract
- Knowledge of species’ habitat requirements can be gained from studying individual variation in home range size, under the assumption that larger home ranges reflect increased resource needs or decreased habitat quality. We used satellite telemetry to delineate home ranges of South Scandinavian Common Cuckoos (Cuculus canorus) throughout their annual cycle. Annual stage (breeding or non-breeding period) and percentage of forest cover were good predictors of home range size. Average breeding season home ranges were ten times as large as those of non-breeding home ranges, suggesting strong temporal variation in the birds’ resource needs, and perhaps lower habitat quality in the breeding range compared to the African part of their annual range. Furthermore, although the Cuckoos rarely chose a home range with complete forest cover, we found a significant negative relationship between forest cover and home range area. This suggests that heterogeneous landscapes which include some dense forest cover constitute important habitat for Cuckoos, and that the continuing trend of forest loss in tropical Africa could reduce habitat quality for the Cuckoo in the non-breeding season.
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