| 1. |
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| 2. |
- Stefanescu, Constanti, et al.
(author)
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Multi-generational long-distance migration of insects: studying the painted lady butterfly in the Western Palaearctic
- 2013
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In: Ecography. - : Wiley. - 1600-0587 .- 0906-7590. ; 36:4, s. 474-486
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Journal article (peer-reviewed)abstract
- Long-range, seasonal migration is a widespread phenomenon among insects, allowing them to track and exploit abundant but ephemeral resources over vast geographical areas. However, the basic patterns of how species shift across multiple locations and seasons are unknown in most cases, even though migrant species comprise an important component of the temperate-zone biota. The painted lady butterfly Vanessa cardui is such an example; a cosmopolitan continuously-brooded species which migrates each year between Africa and Europe, sometimes in enormous numbers. The migration of 2009 was one of the most impressive recorded, and thousands of observations were collected through citizen science programmes and systematic entomological surveys, such as high altitude insect-monitoring radar and ground-based butterfly monitoring schemes. Here we use V. cardui as a model species to better understand insect migration in the Western Palaearctic, and we capitalise on the complementary data sources available for this iconic butterfly. The migratory cycle in this species involves six generations, encompassing a latitudinal shift of thousands of kilometres (up to 60 degrees of latitude). The cycle comprises an annual poleward advance of the populations in spring followed by an equatorward return movement in autumn, with returning individuals potentially flying thousands of kilometres. We show that many long-distance migrants take advantage of favourable winds, moving downwind at high elevation (from some tens of metres from the ground to altitudes over 1000 m), pointing at strong similarities in the flight strategies used by V. cardui and other migrant Lepidoptera. Our results reveal the highly successful strategy that has evolved in these insects, and provide a useful framework for a better understanding of long-distance seasonal migration in the temperate regions worldwide.
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| 3. |
- Alerstam, Thomas, et al.
(author)
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Temporal and spatial patterns of repeated migratory journeys by ospreys
- 2006
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In: Animal Behaviour. - : Elsevier BV. - 1095-8282 .- 0003-3472. ; 71:3, s. 555-566
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Journal article (peer-reviewed)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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| 4. |
- Brattström, Oskar, et al.
(author)
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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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In: Animal Behaviour. - : Elsevier BV. - 1095-8282 .- 0003-3472. ; 76, s. 335-344
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Journal article (peer-reviewed)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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| 5. |
- Dobson, Andrew D. M., et al.
(author)
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The size and migratory origins of the population of Hen Harriers Circus cyaneus wintering in England
- 2012
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In: Bird Study. - : Informa UK Limited. - 0006-3657 .- 1944-6705. ; 59:2, s. 218-227
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Journal article (peer-reviewed)abstract
- Capsule The majority of Hen Harriers Circus cyaneus that spend the winter in England are derived from the British breeding population. Aims To investigate the popular hypothesis that Hen Harriers which over-winter in England are derived principally from breeding populations in mainland Europe. Methods Demographic data were used to estimate numbers of Hen Harriers in Britain at the end of the breeding season. This figure was used, together with data from winter (October-March inclusive) recoveries of Hen Harriers ringed in Britain during the breeding season, to estimate the number of birds from the British breeding population wintering in England and in other parts of Europe. Results It was estimated that Hen Harriers wintering in England are derived primarily from British breeding populations. Published winter population figures for British Hen Harriers may be significant underestimates. Conclusion The link between breeding and wintering populations of Hen Harriers in Britain is closer than previously thought. Conservation action should be spread more equally between the environmental factors which limit populations in different seasons. The winter population in Britain, as monitored by the Hen Harrier Winter Roost Survey, may provide a good indication of the status of the breeding population.
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| 6. |
- Hake, M, et al.
(author)
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Age-dependent migration strategy in honey buzzards Pernis apivorus tracked by satellite
- 2003
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In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 103:2, s. 385-396
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Journal article (peer-reviewed)abstract
- Six adult and three juvenile honey buzzards Pernis apivorus were radio-tracked by satellite during autumn migration from southwestern Sweden. All adults crossed the Mediterranean Sea at the Strait of Gibraltar and continued across the Sahara desert to winter in West Africa, from Sierra Leone to Cameroon. Analysing three main steps of the migration, (1) from the breeding site to the southern Mediterranean region, (2) across the Sahara and (3) from the southern Sahara to the wintering sites, the adults changed direction significantly between these steps, and migrated along a distinct large-scale detour. In contrast, the juveniles travelled in more southerly directions, crossed the Mediterranean Sea at various places, but still ended up in the same wintering areas as the adults. Average speeds maintained on travelling days were similar for the two age groups, about 170 km/day in Europe, 270 km/day across Sahara and 125 km/day in Africa south of Sahara. However, as the adults used fewer stopover days en route, they maintained higher mean overall speeds and completed migration in a shorter time (42 days) than the juveniles (64 days). Although the juveniles set out on more direct courses towards the wintering grounds, they did not cover significantly shorter distances than the adults, as they tended to show a larger directional scatter between shorter flight segments. The results corroborate previous suggestions that adult and juvenile honey buzzards follow different routes during autumn migration, and that the birds change migration strategy during their lifetime. While juveniles may use individual vector orientation, social influences and learning may be of great importance for the detour migration of adults. The remarkable and distinct age-dependent shift in migratory route and orientation of the honey buzzard provides a challenging evolutionary problem.
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| 7. |
- Hake, M, et al.
(author)
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Satellite tracking of Swedish Ospreys Pandion haliaetus: Autumn migration routes and orientation
- 2001
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In: Journal of Avian Biology. - 0908-8857. ; 32:1, s. 47-56
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Journal article (peer-reviewed)abstract
- Autumn migration routes and orientation of Swedish Ospreys Pandion haliaetus were studied by satellite tracking of 18 birds. Of these. 13 could be followed during the entire migration (6 females, 5 males and 2 juveniles). Most birds migrated across western and central Europe to winter in tropical West Africa. However, one juvenile flew to Cameroon and one Female used a very easterly route and reached Mozambique. On average, the birds travelled a total distance of about 6700 km, with little variation except for the female wintering in Mozambique, who travelled more than 10000 km. Of 21 stopovers (of > 1 day), only five were made south of 45 degreesN; three of these in Africa. Females departed before males and juveniles and flew to a stopover site they probably were familiar with. After 3-4 weeks there, they continued to their wintering grounds. Also males and juveniles usually made one or more stopovers. Adults seemed to travel to a known wintering site. where they remained stationary, whereas juveniles were more mobile after reaching tropical regions, probably looking for good wintering sites. Males generally left the breeding area in directions similar to the mean migratory direction, whereas a fen females departed in diverging initial directions. Apart from these diversions, adult Ospreys followed very straight migratory routes. with overall mean directions of 185-209 degrees and with mean angular deviations of 6-33 degrees. Some juveniles also departed in diverging directions. Moreover, young birds tended to show a larger variability in orientation. Thus, the Ospreys kept a fairly straight direction and did not avoid geographical obstacles such as mountain ranges and desert areas. However. they seemed reluctant to cross large water bodies. There was no correlation between angular deviation and length of the migrational segment, indicating that the principles of orientation by vector summation may not be valid for Osprey migration. Moreover, the geographic direction of migration did not vary in accordance with variations in the magnetic declination, suggesting that the Ospreys did not orient along magnetic loxodromes.
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| 8. |
- Jaffre, Mikael, et al.
(author)
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Long-Term Phenological Shifts in Raptor Migration and Climate
- 2013
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In: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:11
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Journal article (peer-reviewed)abstract
- Climate change is having a discernible effect on many biological and ecological processes. Among observed changes, modifications in bird phenology have been widely documented. However, most studies have interpreted phenological shifts as gradual biological adjustments in response to the alteration of the thermal regime. Here we analysed a long-term dataset (1980-2010) of short-distance migratory raptors in five European regions. We revealed that the responses of these birds to climate-induced changes in autumn temperatures are abrupt and synchronous at a continental scale. We found that when the temperatures increased, birds delayed their mean passage date of autumn migration. Such delay, in addition to an earlier spring migration, suggests that a significant warming may induce an extension of the breeding-area residence time of migratory raptors, which may eventually lead to residency.
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| 9. |
- Kjellén, Nils
(author)
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Differential migration in raptors
- 1999
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Doctoral thesis (other academic/artistic)abstract
- Differences between ages, sexes and populations in the timing of migration at Falsterbo, Sweden and in the choice of wintering site among raptors in Scania were investigated. Competition and dominance is the best primary explanation to the results. In most cases the more competitive adults winter north of juveniles and the larger females north of males. Moult strategy is probably one of the most important reasons why females in general migrate south earlier than males, and juveniles ahead of adults, in some short-distance migrants. The proportion of adults and juveniles in Swedish raptors leaving via Falsterbo is calculated. The concentration rate is generally highest in species with a more southerly distribution and in raptors primarily using thermal migration. With a few exceptions juveniles are more concentrated at Falsterbo than adults. An analysis of the long-term systematic migration counts from Falsterbo, shows that in all raptors where the Swedish population trends are reasonably well known from other studies, the fluctuation in numbers is very well reflected in the autumn figures from Falsterbo. The proportion of juvenile birds among the migrants gives a good measure of the annual reproduction in several species. By separating Common Buzzards with a white plumage (mainly with a relatively southerly breeding range) at Falsterbo it was possible to demonstrate some differences in migration pattern compared to darker and more northerly birds. Studies of three species of skuas on the Russian tundra demonstrated interesting differences in the proportion of dark phase. While no dark phase birds seem to occur in Long-tailed Skua the proportion was close to 8 % dark birds in Pomarine Skua all the way from Norway to Wrangel Island. This strongly indicates a gene flow all along the transect in this nomadic species. In Arctic Skua on the other hand there was an abrupt change from 64 % dark phase on the Kola Peninsula to an almost complete dominance of light birds all along the Russian tundra. Satellite transmitters constitute an invaluable tool enabling detailed studies of the migration strategies of individual birds. Thirteen Ospreys were tracked on autumn migration from Sweden to the wintering grounds in tropical Africa. The average speed for the whole journey was 174 km/day. This is similar to migration speeds in other raptors studied by satellite telemetry, but considerably faster than results from ringing recoveries. There was large individual variation with few major differences between sexes and ages. The birds made between 0 and 4 stopovers along the way. Migration took place only during the light hours and the Ospreys spent about nine hours in active flight on travelling days.
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| 10. |
- Kjellén, Nils, et al.
(author)
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Population trends in Swedish raptors demonstrated by migration counts at Falsterbo, Sweden 1942-97
- 2000
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In: Bird Study. - 0006-3657. ; 47:2, s. 195-211
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Journal article (peer-reviewed)abstract
- The autumn migration of raptors at Falsterbo, Sweden has been studied since the early 1940s, and from 1973 standardized counts were made. Here we present data for 15 species over a 39-year period from 1942-97. These are discussed in the context of available information on population trends in Sweden and neighbouring countries. Although annual numbers and concentration rate vary considerably between species, population changes are very well reflected in the migration figures from Falsterbo. Most raptors showed stable populations at a fairly high level during the 1940s, hilt a marked decline was already obvious in White-tailed Eagle Haliaeetus albicilla and Peregrine Falcon Falco peregrinus. During the 1950s and 1960s, a more or less steep decline occurred in most species. Four species started to increase during the 1960s, but the real change came during the 1970s. At that time, decreased human persecution and a reduction ill the effects from pesticides resulted ill a general increase in Scandinavian raptors, with only Honey Buzzard Pernis apivorus continuing to decrease. The increases continued during the 1980s, but in the 1990s many raptors seem to have reached stable numbers or to have started to decline again. Two species, Marsh Harrier Circus aeruginosus and Montagu's Harrier C. pygargus show a positive trend through the study period. Numbers of Northern Harrier Circus cyaneus, Rough-legged Buzzard Buteo lagopus and Eurasian Kestrel Falco tinnunculus stabilized during Me 1980s and show a clear decline since then, most probably due to a general lack of rodent peaks in Northern Scandinavia since 1982. Most species of raptors scent to he doing reasonably well at the moment, brit a continuous decline in Honey Blizzard and Common Buzzard Buteo buteo is disturbing, and is possibly due to declining proportions of old deciduous forest and grazed meadows in Scandinavia. Since a general census programme of birds of prey does not exist in Sweden, the migration counts at Falsterbo is the best general method of monitoring population changes.
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| 11. |
- Kjellén, Nils
(author)
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Sträckfågelräkningar vid Falsterbo hösten 2002
- 2002
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Reports (other academic/artistic)abstract
- BAKGRUND De standardiserade höst räk ning ar nai Na tur vårds ver kets regi påbörjades hösten1973 som en del i deras fågelmonitoring. Frånoch med 2001 ansvarar undertecknad för dessaräk ning ar. Från detta år påbörjas räkningarnaden 1 au gus ti (i stället för 11 augusti), främstför att er hål la en mer fullständig täckning avrov få gel sträck et. Vidare artbestäms lommar,fi sk/sil ver tär nor, och korsnäbbar, vilket ej skettti di ga re. I mån av tid åldersbestämdes storkar,sång sva nar, prutgäss, rovfåglar, vissa vadare,labbar, dvärg mås, silltrut och tärnor för atterhålla ett mått på årets ungproduktion.Åren 1986-2000 har höststräcket av rov fåg laröver halvön specialstuderats (Kjellén 2001 ochtidigare). Räkningarna har då skett på sam masett som höstarna 2001-2002. En jäm fö rel semellan denna serie och de standardiseraderäk ning ar na visar en signifi kant korrelationför samt li ga rovfåglar. Jag har därför valt att räkna upp de standardiserade siffrorna från1973-1985 med den genomsnittliga skillnadenunder femtonårsserien 1986-2000. Mer detaljerbe träf fan de omräkning av siffror för olika arterpre sen te ras av Kjellén (2002).
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| 12. |
- Kjellén, Nils
(author)
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Sträckfågelräkningar vid Falsterbo hösten 2003
- 2003
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Reports (other academic/artistic)abstract
- Räkningar i Naturvårdsverkets regi bedrevs mellan 1 augusti och 20 november. Den övervägandemajoriteten av arterna räknades medan åldern bestämdes för rovfåglar och vissa andra grupper.Jämfört med tidigare år bokfördes en genomsnittlig totalsumma. Flertalet rovfåglar räknades i relativthöga antal och ungfågelsandelen var rekordhög. Positivt var även att fl era tropikfl yttare uppträddemer talrikt än på många år Allmänt gynnades sträcket av dominerande västvindar och generelltverkar häckningen ha gått förhållandevis bra. En relativt dålig frö- och fruktsättning gjordeatt många invasionsarter var i rörelse.
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| 13. |
- Kjellén, Nils
(author)
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Sträckfågelräkningar vid Falsterbo hösten 2004
- 2004
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Reports (other academic/artistic)abstract
- Räkningar i Naturvårdsverkets regi bedrevs mellan 1 augusti och 20 november. Den övervägandemajoriteten av arterna räknades medan åldern bestämdes för rovfåglar och vissa andra grupper.Dominerande västvindar är en av anledningarna till den förhållandevis höga totalsumman. Flerarovfåglar räknades i relativt höga antal och för några minskande arter verkar trenden snarast havänt. Ungfågelsandelen var återigen rekordhög. Positivt var även att några tropikflyttare uppträddemer talrikt än på många år. Dessutom sträckte flertalet finkfåglar i rekordhöga antal. De flestainvasionsarter uppträddedäremot i måttliga antal, men sidensvansen sträckte i ej tidigare skådademängder.
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| 14. |
- Kjellén, Nils
(author)
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Sträckfågelräkningar vid Falsterbo hösten 2006
- 2006
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Reports (other academic/artistic)abstract
- Räkningar i Naturvårdsverkets regi bedrevs mellan 1 augusti och 20 november. Den övervägandemajoriteten av arterna räknades medan åldern bestämdes för rovfåglar och vissa andra grupper.Dominerande västvindar och god ungproduktion ligger sannolikt bakom den förhållandevis högatotalsumman. Flertalet rovfåglar räknades i relativt höga antal trots att ungfågelsandelen endastvar genomsnittlig. Uppgången fortsätter för flertalet ökande arter medan det finns indikationer påatt trenden vänt för en del fågelarter som minskat långsiktigt. Slående var den totala avsaknadenav invasionsarter.
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| 15. |
- Kjellén, Nils
(author)
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Sträckfågelräkningar vid Falsterbo hösten 2007
- 2007
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Reports (other academic/artistic)abstract
- Räkningar i Naturvårdsverkets regi bedrevs mellan 1 augusti och 20 november. Den övervägandemajoriteten av arterna räknades medan åldern bestämdes för rovfåglar och vissa andra grupper.Totalsumman ligger något över genomsnittet. Uppgången fortsätter för flertalet ökande artermedan det finns indikationer på att trenden vänt för en del fågelarter som minskat långsiktigt. Endel tropikflyttande rovfåglar var relativt fåtaliga medan fjällvråken uppvisade det bästa resultatetsedan 1982. Medan tropikflyttande tättingar var relativt talrika räknades många senhöstflyttare ilåga antal efter en kall inledning på oktober. Bland invasionsarter märktes blåmes, grönsiska ochkorsnäbbar.
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| 16. |
- Kjellén, Nils
(author)
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Sträckfågelräkningar vid Falsterbo hösten 2008
- 2009
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Reports (other academic/artistic)abstract
- Räkningar i Naturvårdsverkets regi bedrevs mellan 1 augusti och 20 november. Den övervägande majoriteten av arterna räknades medan åldern bestämdes för rovfåglar och vissa andra grupper. Sammantaget en bra säsong där totalsumman ligger väl över genomsnittet. Uppgången fortsätter för flertalet långsiktigt ökande arter medan listan med signifikant minskande arter sakta krymper något. Även om den genomsnittliga ungfågelsandelen låg något under medel uppträdde flertalet rovfåglar talrikt, med exempelvis nya rekordnoteringar för röd glada och sparvhök. Lågtryckspassager i augusti gav höga antal av adulta vadare och tärnor. Flera tropikflyttande tättingar räknades i relativt höga antal och den milda senhösten borgade för goda siffror för flertalet kortflyttare. Bland invasionsarterna registrerades måttliga rörelser av främst större hackspett, sidensvans, stjärtmes, blåmes, nötkråka och gråsiska.
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| 17. |
- Kjellén, Nils, et al.
(author)
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Timing and speed of migration in male, female and juvenile Ospreys Pandion haliaetus between Sweden and Africa as revealed by field observations, radar and satellite tracking
- 2001
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In: Journal of Avian Biology. - 0908-8857. ; 32:1, s. 57-67
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Journal article (peer-reviewed)abstract
- Breeding Ospreys were studied in southern Sweden and 13 birds were tracked by satellite telemetry on autumn migration to the African wintering grounds. This was supplemented with studies of migrating birds at Falsterbo and radar trackings From southern Sweden. Females generally left the nest site 2-3 weeks ahead of males and juveniles. Among males, failed bleeders migrated significantly earlier than successful breeders. At Falsterbo, Ospreys passed in the order adult females (median 22 Aug), adult males (26 Aug) and juveniles (30 Aug). Birds tracked by radar achieved cross-country speeds of 18-47 km/h. Most of our birds wintered in an area from The Gambia to the Ivory Coast, with one juvenile in Cameroon and one Female in Mozambique. Ospreys spent on average 45 days travelling an average distance of 6742 km with no significant differences between sex and age categories. Between 0 and 44 days were used for stopovers en route. Females generally made more stopovers at northerly latitudes than males. Average speed on migration was 174 km/d, which is similar to speeds reported for other large raptors followed by satellite. Speed on travelling days was on average 257 km/d with males generally moving fastest. There was a clear tendency for lower speeds and more stopovers in Europe than during the crossing of the Sahara. Migratory activity generally rook place between 8 a. m. and 5 p. m. local time and we have no indications of birds flying at night. With 9 hours travelling rime the expected cross-country speed, derived from the theor of thermal soaring flight and assuming thermal climb rates of 1-2 m/s, varies from 251 to 360 km/d, which is similar to the observed mean spaed on travelling days. Even so, one male travelled 746 km/d between Sweden and Spain. Some Ospreys need a much larger fraction of travelling days than expected from theory, suggesting that they deposit fuel on the breeding grounds before departure. This is supported by a correlation between the observed fraction of days spent travelling and departure date. In late departing Ospreys, especially males and juveniles, a major part of the energy for migration is probably deposited on the breeding grounds.
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| 18. |
- Krebs, C. J., et al.
(author)
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Terrestrial trophic dynamics in the Canadian Arctic
- 2003
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In: Canadian Journal of Zoology-Revue Canadienne De Zoologie. ; 81, s. 827-843
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Journal article (peer-reviewed)abstract
- The Swedish Tundra Northwest Expedition of 1999 visited 17 sites throughout the Canadian Arctic. At 12 sites that were intensively sampled we estimated the standing crop of plants and the densities of herbivores and predators with an array of trapping, visual surveys, and faecal-pellet transects. We developed a trophic-balance model using ECOPATH to integrate these observations and determine the fate of primary and secondary production in these tundra ecosystems, which spanned an 8-fold range of standing crop of plants. We estimated that about 13% of net primary production was consumed by herbivores, while over 70% of small-herbivore production was estimated to flow to predators. Only 9% of large-herbivore production was consumed by predators. Organization of Canadian Arctic ecosystems appears to be more top-down than bottom-up. Net primary production does not seem to be herbivore-limited at any site. This is the first attempt to integrate trophic dynamics over the entire Canadian Arctic.
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| 19. |
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| 20. |
- Nils Kjellén,
(author)
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Sträckfågelräkningar vid Falsterbo hösten 2005
- 2005
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Reports (other academic/artistic)abstract
- Räkningar i Naturvårdsverkets regi bedrevs mellan 1 augusti och 20 november. Den övervägandemajoriteten av arterna räknades medan åldern bestämdes för rovfåglar och vissa andra grupper.Dominerandevästvindar och god ungproduktion ligger sannolikt bakom den förhållandevis högatotalsumman. De flesta rovfåglarna räknades i relativt höga antal medan ungfågelsandelen varnågotlägre än 2004. Uppgången fortsätter för flertalet ökande arter medan det finns indikationerpå att trenden vänt för en del fågelarter som minskat långsiktigt. Relativt få invasionsarter passerade,men höga antal noterades för sidensvans, domherre och gråsiska.
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| 21. |
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| 22. |
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| 23. |
- Thorup, K, et al.
(author)
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Bird orientation: compensation for wind drift in migrating raptors is age dependent
- 2003
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In: Royal Society of London. Proceedings B. Biological Sciences. - : The Royal Society. - 1471-2954. ; 270:suppl. 1, s. 8-11
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Journal article (peer-reviewed)abstract
- Despite the potentially strong effect of wind on bird orientation, our understanding of how wind drift affects migrating birds is still very limited. Using data from satellite-based radio telemetry, we analysed the effect of changing winds on the variation of the track direction of individual birds. We studied adults and juveniles of two raptor species, osprey Pandion haliaetus and honey buzzard Pernis apivorus, on autumn migration between North Europe and Africa, and demonstrate an important difference between the age categories of both species in the extent of wind drift. For juveniles, side- and following-wind components affected the rates of movement perpendicular to and along the mean direction, respectively, to a similar degree, suggesting full wind drift. By contrast, for adults the rate of crosswind displacement was significantly smaller than the effect of wind on forward movement, showing much reduced wind drift (29%). This indicates that adults have acquired a more sophisticated orientation system, permitting detection of and compensation for wind drift, than juveniles. These drift effects are likely to reduce the ability of juveniles to locate species-specific wintering areas in case of rapid climatic wind change.
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| 24. |
- Thorup, K, et al.
(author)
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Can vector summation describe the orientation system of juvenile ospreys and honey buzzards? - An analysis of ring recoveries and satellite tracking
- 2003
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In: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 103:2, s. 350-359
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Journal article (peer-reviewed)abstract
- Juvenile bird migrants are generally believed to use a clock-and-compass migratory orientation strategy. According to such a strategy migrants accomplish their migration by flying a number of successive flight steps with direction and number of steps controlled by an endogenous programme. One powerful way of testing this is by comparing predictions from a model of such a strategy with observed patterns. We used data from ringing and satellite-based radio telemetry to investigate the orientation system of juvenile ospreys (Pandion haliaetus) and honey buzzards (Pernis apivorus) migrating from Sweden to tropical west Africa. The ring recoveries showed a much larger scatter in the orientation of ospreys than of honey buzzards, but there was only a slight such difference in the satellite tracks. These tracks of individuals of both species were rather straight with a high directional concentration per step. The honey buzzard. data showed a close fit to a simple vector summation model, which is expected if birds follow a clock-and-compass strategy. However, the osprey data did not fit such a simple model, as ring recoveries showed a significantly greater deviation at short distances than predicted on the basis of long distance data. Satellite tracking also indicated less concentrated orientation on short distances. The pattern observed for the osprey can generally be explained by an extended vector summation model, including an important element of pre-migration dispersal. The existence of extensive dispersal in the osprey stands in contrast to the apparent absence of such dispersal in the honey buzzard. The explanation for this difference between the species is unclear. The model of orientation by vector summation is very sensitive to the existence of differences in mean direction between individuals. Assuming such differences, as tentatively indicated by the satellite tracking data, makes simple compass orientation by vector summation inconsistent with the distribution of ring recoveries at long distances, with a high proportion of misoriented birds falling outside the normal winter range.
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| 25. |
- Thorup, K, et al.
(author)
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Do migratory flight paths of raptors follow constant geographical or geomagnetic courses?
- 2006
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In: Animal Behaviour. - : Elsevier BV. - 1095-8282 .- 0003-3472. ; 72:4, s. 875-880
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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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| 26. |
- Thorup, K, et al.
(author)
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Traveling or stopping of migrating birds in relation to wind: an illustration for the osprey
- 2006
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In: Behavioral Ecology. - : Oxford University Press (OUP). - 1045-2249 .- 1465-7279. ; 17:3, s. 497-502
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Journal article (peer-reviewed)abstract
- Although it is often assumed that birds strongly prefer tailwinds for their migratory flights, we predict that a strategy of no wind selectivity (traveling independently of winds) may be more favorable than wind selectivity (traveling on tailwind occasions but stopping to rest under headwind occasions) for birds with low energy costs of travel relative to rest and for birds that cannot use stopover time for efficient fuel deposition. We test this prediction by analyzing the daily traveling or stopping as recorded by satellite tracking of five ospreys Pandion haliaetus, a species often using energy-saving thermal soaring, during their migration between northern Europe and Africa. Besides wind, precipitation is another weather factor included in the analyses because thermal soaring migrants are expected to stop and rest in rainy weather. In logistic regression analyses, taking into account the effects of latitude, behavior on previous day, season, date, and individual for discriminating between traveling and stopping days, we found a lack of influence of winds, suggesting that the ospreys travel or stop without regard to wind. This lack of wind selectivity under light and moderate winds is in agreement with our prediction. We expect a low degree of wind selectivity and thus regular flights under headwinds also among other types of birds that cannot use stopping time for efficient foraging and fuel deposition. We also found an unexpected lack of influence of precipitation, possibly because of relatively few instances with rainfall in combination with poor geographic precision for estimates of this weather variable.
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| 27. |
- Wiklund, Christer G., et al.
(author)
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Lemming predators on the Siberian tundra
- 1999
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In: Ambio. - 0044-7447 .- 1654-7209. ; 28:3, s. 281-286
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Journal article (peer-reviewed)abstract
- In the Eurasian Arctic, the most common lemming species are the Siberian lemming (Lemmus sibiricus) and the collared lemming (Dicrostonyx torquatus). Lemmings constitute the main food item for 5 common predators in the area: arctic fox; snowy owl; rough-legged buzzard; long-tailed skua; and pomarine skua. Hence, these predators form a foraging guild. We have studied factors influencing the structure of this guild. When comparing cooccurrence of the predators between 17 sites across Siberia, there were positive associations between the snowy owl and the two skuas, and a negative association between snowy owl and rough-legged buzzard. There was also a large variation in local population density among the predators, conceivably, due to the risk of intra-guild predation as well as the variation in food supply. There were significant relationships between lemming abundance and the abundance of each predator. An analysis of the predatory response by the arctic fox indicated a response pattern similar to that of a delayed numerical response to lemming abundance. For this and other reasons, we propose that the arctic fox is a resident specialist predator on microtine rodents. Further, the birds appeared to be nomadic specialist predators with, perhaps, one exception, the rough-legged buzzard.
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