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| 2. |
- Boström, Jannika, et al.
(författare)
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Autumn migratory fuelling : a response to simulated magnetic displacement in juvenile wheatears, Oenathe oenathe
- 2010
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Ingår i: Behavioral Ecology and Sociobiology. - : Springer Science and Business Media LLC. - 0340-5443 .- 1432-0762. ; 64:11, s. 1725-1732
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Tidskriftsartikel (refereegranskat)abstract
- Recent experiments exposing migratory birds to altered magnetic fields simulating geographical displacements have shown that the geomagnetic field acts as an external cue affecting migratory fuelling behaviour. This is the first study investigating fuel deposition in relation to geomagnetic cues in long-distance migrants using the western passage of the Mediterranean region. Juvenile wheatears (Oenanthe oenanthe) were exposed to a magnetically simulated autumn migration from southern Sweden to West Africa. Birds displaced parallel to the west of their natural migration route, simulating an unnatural flight over the Atlantic Ocean, increased their fuel deposition compared to birds experiencing a simulated migration along the natural route. These birds, on the other hand, showed relatively low fuel loads in agreement with earlier data on wheatears trapped during stopover. The experimental displacement to the west, corresponding to novel sites in the Atlantic Ocean, led to a simulated longer distance to the wintering area, probably explaining the observed larger fuel loads. Our data verify previous results suggesting that migratory birds use geomagnetic cues for fuelling decisions and, for the first time, show that birds, on their first migration, can use geomagnetic cues to compensate for a displacement outside their normal migratory route, by adjusting fuel deposition.
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| 3. |
- Cresswell, Will, et al.
(författare)
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Does an opportunistic predator preferentially attack nonvigilant prey?
- 2003
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Ingår i: Animal Behaviour. - : Elsevier BV. - 0003-3472 .- 1095-8282. ; 66:4, s. 643-648
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Tidskriftsartikel (refereegranskat)abstract
- The dilution effect as an antipredation behaviour is the main theoretical reason for grouping in animals and states that all individuals in a group have an equal risk of being predated if equally spaced from each other and the predator. Stalking predators, however, increase their chance of attack success by preferentially targeting nonvigilant individuals, potentially making relative vigilance rates in a group relatively important in determining predation compared with the dilution effect. Many predators, however, attack opportunistically without stalking, when targeting of nonvigilant individuals may be less likely, so that the dilution effect will then be a relatively more important antipredation reason for grouping. We tested whether an opportunistically hunting predator, the sparrowhawk, Accipiter nisus, preferentially attacked vigilant or feeding prey models presented in pairs. We found that sparrowhawks attacked vigilant and feeding mounts at similar frequencies. Our results suggest that individuals should prioritize maximizing group size or individual vigilance dependent on the type of predator from which they are at risk. When the most likely predator is a stalker, individuals should aim to have the highest vigilance levels in a group, and there may be relatively little selective advantage to being in the largest group. In contrast, if the most likely predator is an opportunist, then individuals should simply aim to be in the largest group and can also spend more time foraging without compromising predation risk. For most natural systems this will mean a trade-off between the two strategies dependent on the frequency of attack of each predator type.
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| 5. |
- Hedlund, Johanna, 1982-
(författare)
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Climate change effects on migratory birds and on the ecology and behaviour of the willow warbler (Phylloscopus trochilus)
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Recent global climate change is influencing the behaviour and ecology of species worldwide. Birds are typical systems to study in this context, as they are often migratory and thus subjected to a variety of environmental effects. This thesis employs the use of long-term ringing records, field observations, historical maps and historical volunteer observations with the aim of describing behavioural and ecological responses of birds to the current environmental change. An investigation into the spring arrival, reproduction and autumn departure in willow warblers (Phylloscopus trochilus) breeding at a southern study site in Sweden (65°N 18°E) showed that all three phenological events had advanced in parallel. Thus birds arrive earlier, start breeding earlier and leave Sweden earlier, with the breeding period staying the same in length. By teasing apart the migratory responses of different individuals, it became clear that particularly early arriving males and early departing juveniles had advanced migration. However, willow warblers migrating past a northern study site in Sweden (65°N 23°E) displayed no change in autumn departure. When migration in the two regionally separate populations were analyzed in relation to climatic variables, the results indicated that foremost a combined effect of growing season onset and the North Atlantic Oscillation influenced migratory timing, and only in individuals that had advanced migration. As growing season onset had advanced at both regions, but only elicited migratory change in southern willow warblers, it is proposed that intra-specific difference between populations prepare them differently to climate change. Willow warblers breeding at northern latitudes were also displaying absence of an otherwise common behaviour of the species: philopatry. It is suggested that the climate induced change in onset of the growing season, coupled with an increase in available territories, could have enabled a southern influx of dispersal-prone birds adopting a less philopatric breeding behaviour. Availability of territories was also studied in southern Sweden, in relation to 100 years of land use change and future climate change effects on forestry. The mass-conversion of grazed forest into coniferous sylvicultures that has occurred in Sweden 1900-2013 was shown to have negatively affected territory availability for willow warblers. The second most common bird species in Sweden, the chaffinch (Fringilla coelebs), was however shown to be largely unaffected. In a future scenario where rising temperatures will increase growth rates of trees, harvest rotation will be faster and both sylvicultures and logged areas will increase in coverage, favouring both species. Thus commonness in terms of landscape and species occurrence has altered historically and is dynamically linked. Historic perspectives were also applied to observations of spring arrival of 14 migratory bird species. A relative comparison of two data sets, collected over 140 years, revealed that short-distance migrants have changed their spring arrival more than long-distance migrants in southern Sweden. In conclusion, the results of this thesis provide insights into climate change effects on avian behaviour and ecology, document unique observations and contribute with a great spectrum of knowledge, from exact details on responses by individual birds, through long-term changes in populations to historical perspectives on shifts in entire landscapes
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| 6. |
- Hedlund, Johanna, et al.
(författare)
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Increase in protandry over time in a long-distance migratory bird
- 2022
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Ingår i: Ecology and Evolution. - : Wiley. - 2045-7758. ; 12:7
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Tidskriftsartikel (refereegranskat)abstract
- Protandry is a widespread life-history phenomenon describing how males precede females at the site or state of reproduction. In migratory birds, protandry has an important influence on individual fitness, the migratory syndrome, and phenological response to climate change. Despite its significance, accurate analyses on the dynamics of protandry using data sets collected at the breeding site, are lacking. Basing our study on records collected during two time periods, 1979 to 1988 and 2006 to 2016, we aim to investigate protandry dynamics over 38 years in a breeding population of willow warblers (Phylloscopus trochilus). Change in the timing of arrival was analyzed in males and females, and protandry (number of days between male and female arrival) was investigated both at population level and within breeding pairs. Our results show advancement in the arrival time at the breeding site in both sexes, but male arrival has advanced to a greater extent, leading to an increase in protandry both at the population level and within breeding pairs. We did not observe any change in sex ratio that could explain the protandry increase, but pronounced temperature change has occurred and been reported in the breeding area and along the migratory route. Typically, natural selection opposes too early arrival in males, but given warmer springs, this counteracting force may be relaxing, enabling an increase in protandry. We discuss whether our results suggest that climate change has induced sex-specific effects, if these could be evolutionary and whether the timing of important life-history stages such as arrival at the breeding site may change at different rates in males and females following environmental shifts.
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| 7. |
- Hedlund, Johanna S. U., et al.
(författare)
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Long-term phenological shifts and intra-specific differences in migratory change in the willow warbler Phylloscopus trochilus
- 2015
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Ingår i: Journal of Avian Biology. - : Wiley. - 0908-8857 .- 1600-048X. ; 46:1, s. 97-106
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Tidskriftsartikel (refereegranskat)abstract
- Climate change can influence many aspects of avian phenology and especially migratory shifts and changes in breeding onset receive much research interest in this context. However, changes in these different life-cycle events in birds are often investigated separately and by means of ringing records of mixed populations. In this long-term study on the willow warbler Phylloscopus trochilus, we investigated timing of spring and autumn migration in conjunction with timing of breeding. We made distinction among individuals with regard to age, sex, juvenile origin and migratory phase. The data set comprised 22-yr of ringing records and two temporally separated data sets of egg-laying dates and arrival of the breeding population close to the ringing site. The results reveal an overall advancement consistent in most, but not all, phenological events. During spring migration, early and median passage of males and females became earlier by between 4.4 to 6.3 d and median egg-laying dates became earlier by 5 d. Male arrival advanced more, which may lead to an increase in the degree of protandry in the future. Among breeding individuals, only female arrival advanced in timing. In autumn, adults and locally hatched juvenile females did not advanced median passage, but locally hatched juvenile males appeared 4.2 d earlier. Migrating juvenile males and females advanced passage both in early and median migratory phase by between 8.4 to 10.1 d. The dissimilarities in the response between birds of different age, sex and migratory phase emphasize that environmental change may elicit intra-specific selection pressures. The overall consistency of the phenological change in spring, autumn and egg-laying, coupled with the unchanged number of days between median spring and autumn migration in adults, indicate that the breeding area residence has advanced seasonally but remained temporally constant.
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| 8. |
- Hedlund, Johanna S. U., et al.
(författare)
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Point of no return – absence of returning birds in the otherwise philopatric willow warbler Phylloscopus trochilus
- 2017
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Ingår i: Journal of Avian Biology. - : Wiley. - 0908-8857 .- 1600-048X. ; 48:3, s. 399-406
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Tidskriftsartikel (refereegranskat)abstract
- The return of individual birds to a specific area in successional years, i.e. philopatry, is a remarkable behavioural trait. Here we report on the remarkably reversed: the complete absence of returning individuals of a migratory passerine with otherwise pronounced philopatry. At a high latitude study site in Abisko (68°32ʹN, 18°80ʹE) in northern Sweden none of the banded adult willow warblers Phylloscopus trochilus returned to breed 2011–2014. This is in stark contrast to all other reports in the literature and also to our two southern study sites (at 56°56ʹN, 18°10ʹE and at 58°94ʹN, 17°14ʹE) where 18–38% of adults returned. We investigated this aberrant pattern found in Abisko by analysing three parameters known to influence philopatry; nest predation, breeding success and breeding density, and predicted that absence of philopatry should co-occur with low breeding success, low breeding density and/or high nest predation. The results did not corroborate this, except that breeding density was lower at Abisko (49–71 pairs km–2) than at the southern sites (106 pairs km–2, 101 pairs km–2). Instead, we suggest the hypothesis that the absence of philopatry is caused by an influx of southern, dispersal-prone individuals deploying another breeding strategy and that this intra-specific range expansion is enabled by milder climate and low population density.
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| 9. |
- Henshaw, Ian, et al.
(författare)
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Food intake and fuel deposition in a migratory bird is affected by multiple as well as single-step changes in the magnetic field
- 2008
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Ingår i: Journal of Experimental Biology. - : The Company of Biologists. - 0022-0949 .- 1477-9145. ; 211, s. 649-653
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies have shown that migratory thrush nightingales (Luscinia luscinia) experimentally treated with multiple changes of the magnetic field simulating a journey to their target stopover area in northern Egypt, increased fuel deposition as expected in preparation to cross the Sahara desert. To investigate the significance of food intake on the body mass changes observed, in the work described here we analysed food intake of the nightingales under study in those earlier experiments. Furthermore, to study whether a single change in the magnetic field directly to northern Egypt is sufficient to provide information for fuelling decisions, we performed a new experiment, exposing thrush nightingales trapped in Sweden, directly to a magnetic field of northern Egypt. Our results show that an experimentally induced magnetic field of northern Egypt, close to the barrier crossing, triggers the same response in fuel deposition as experiments with multiple changes of the magnetic field simulating a migratory journey from Sweden to Egypt, suggesting that migratory birds do not require successive changes in field parameters to incorporate magnetic information into their migratory program. Furthermore, irrespective of experimental set up (single or multiple changes of the magnetic field parameters) increase in food intake seems to be the major reason for the observed increase in fuelling rate compared with control birds, suggesting that geomagnetic information might trigger hormonal changes in migratory birds enabling appropriate fuelling behaviour during migration.
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| 10. |
- Henshaw, Ian, et al.
(författare)
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Geomagnetic field affects spring migratory direction in a long distance migrant
- 2010
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Ingår i: Behavioral Ecology and Sociobiology. - : Springer Science and Business Media LLC. - 0340-5443 .- 1432-0762. ; 64:8, s. 1317-1323
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Tidskriftsartikel (refereegranskat)abstract
- Night-migrating song birds travel to and from their wintering and breeding areas often separated thousands of kilometers apart and are clearly capable of finding intended goal areas from a distant location. Displacement experiments provide a useful way to highlight orientation and navigational skills in migrants. To investigate which cues birds actually use to compensate for displacement and the exact mechanism of each cue, experiments with manipulation of single cues are required. We conducted a simulated displacement of lesser whitethroats Sylvia curruca on spring migration. Birds were displaced not geographically but in geomagnetic space only, north and south of their breeding area to test whether they incorporate information from the geomagnetic field to find their breeding area. Lesser whitethroats held in southeast Sweden but experiencing a simulated displacement north of their breeding area (Norway) failed to show a consistent direction of orientation, whereas birds displaced south of their breeding area (Czech Republic) exhibited consistent northerly orientation, close to the expected seasonally appropriate direction, after displacement toward the trapping location. The absence of a clear compensatory direction in birds displaced north might be due to unfamiliar magnetic information or lack of sufficient information such as a magnetic gradient when moving around. By isolating one orientation cue, the geomagnetic field, we have been able to show that lesser whitethroats might incorporate geomagnetic field information to determine latitude during spring migration.
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