| 1. |
- Boström, Jannika, et al.
(författare)
-
Autumn migratory fuelling : a response to simulated magnetic displacement in juvenile wheatears, Oenathe oenathe
- 2010
-
Ingår i: Behavioral Ecology and Sociobiology. - : Springer Science and Business Media LLC. - 0340-5443 .- 1432-0762. ; 64:11, s. 1725-1732
-
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.
|
|
| 2. |
- Boström, Jannika E., et al.
(författare)
-
The flicker fusion frequency of budgerigars (Melopsittacus undulatus) revisited
- 2017
-
Ingår i: Journal of Comparative Physiology A. Sensory, neural, and behavioral physiology. - : SPRINGER. - 0340-7594 .- 1432-1351. ; 203:1, s. 15-22
-
Tidskriftsartikel (refereegranskat)abstract
- While color vision and spatial resolution have been studied in many bird species, less is known about the temporal aspects of bird vision. High temporal resolution has been described in three species of passerines but it is unknown whether this is specific to passerines, to small actively flying birds, to insectivores or to birds living in bright habitats. Temporal resolution of vision is commonly tested by determining the flicker fusion frequency (FFF), at which the eye can no longer distinguish a flickering light from a constant light of equal intensity at different luminances. Using a food reward, we trained the birds to discriminate a constant light from a flickering light, at four different luminances between 750 and 7500 cd/m(2). The highest FFF found in one bird at 3500 cd/m(2) was 93 Hz. Three birds had higher FFF (82 Hz) at 7500 cd/m(2) than at 3500 cd/m(2). Six human subjects had lower FFF than the birds at 1500 but similar FFF at 750 cd/m(2). These results indicate that high temporal resolution is not a common trait for all small and active birds living in bright light habitats. Whether it is typical for passerines or for insectivorous birds remains to be tested.
|
|
| 3. |
- Boström, Jannika E., et al.
(författare)
-
Ultra-Rapid Vision in Birds
- 2016
-
Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 11:3
-
Tidskriftsartikel (refereegranskat)abstract
- Flying animals need to accurately detect, identify and track fast-moving objects and these behavioral requirements are likely to strongly select for abilities to resolve visual detail in time. However, evidence of highly elevated temporal acuity relative to non-flying animals has so far been confined to insects while it has been missing in birds. With behavioral experiments on three wild passerine species, blue tits, collared and pied flycatchers, we demonstrate temporal acuities of vision far exceeding predictions based on the sizes and metabolic rates of these birds. This implies a history of strong natural selection on temporal resolution. These birds can resolve alternating light-dark cycles at up to 145 Hz (average: 129, 127 and 137, respectively), which is ca. 50 Hz over the highest frequency shown in any other vertebrate. We argue that rapid vision should confer a selective advantage in many bird species that are ecologically similar to the three species examined in our study. Thus, rapid vision may be a more typical avian trait than the famously sharp vision found in birds of prey.
|
|
| 4. |
- Boström, Jannika
(författare)
-
Magnetic map sense in animals: effects of geographic and magnetic displacements
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Migration research is a large and diverse field and in my thesis I have focused on the impact of geomagnetic cues on animal orientation, navigation and migratory fuelling. Several animal species from widely different taxa possess the ability to sense and make use of geomagnetic information during migratory or homing events. I used a map showing isolines for magnetic total field intensity and inclination to investigate the prerequisites for geomagnetic bi-coordinate navigation on a global scale. Areas with narrow or no angular difference between isolines (“no-grid” zones) were considered hard or impossible to navigate within, whereas areas with angular differences of 30° or more were considered ideal. For “no-grid” zones stretching in a north-south direction, the same geomagnetic combination can be encountered on either side of the zone, which may potentially cause problems for migrating animals passing these zones. In order to gain a deeper understanding about how the geomagnetic field may influence animals I gathered publications presenting data from experiments displacing animals in geomagnetic, but not geographic, space. I found 20 studies presenting 40 different experiments with eight species from four taxa. Some of the experiments only altered one magnetic parameter, which sometimes resulted in non-existent magnetic combinations or combinations found at distant locations. It was often not possible to determine whether the animals had used uni- or bi-coordinate navigation. Experiments with loggerhead sea turtles (Caretta caretta) suggested that this species might display different orientation in different intervals of magnetic combinations or alter its orientation after passing a certain “threshold” value or “signpost”. Migratory birds can use the geomagnetic field to make fuelling decisions, which seem to be based on the experience of a decreasing or increasing gradient and not on exact magnetic combinations. Why animals sometimes, but not always, respond to displacement to non-existent or distant magnetic combinations needs more investigation. Two of my studies focus on migratory fuelling in juvenile northern wheatears (Oenanthe oenanthe) magnetically displaced along their migration route, or parallel and to the west of their migration route to simulate a situation where the birds have been drifted off course. I found that the juvenile northern wheatears displaced to a position south of Greenland, due west of the experimental site, increased more in body mass than individuals displaced along the migration route. These birds also ended up at a higher body mass than birds kept in the ambient magnetic field in Sweden and wheatears displaced south along the migration route or south of the position close to Greenland. The position south of Greenland had a higher inclination and field intensity than the ambient geomagnetic field in Sweden, which seem to have been the cues that the birds responded to. In the last study we displaced Russian juvenile wheatears geographically in the high Arctic, from their breeding grounds in northeast Russia, across the north pole to Svalbard. During the transect we performed orientation experiments on the sea ice and the inexperienced birds managed to choose a meaningful mean orientation, that would lead them the closest way to their wintering area, in three out of twelve experiments, one at a location with an inclination of 89.3°. The displaced wheatears experienced very challenging conditions with steep inclination angles, magnetic storms and overcast skies and it is remarkable that they managed to orient at least at some of the test locations.
|
|
| 5. |
- Boström, Jannika, et al.
(författare)
-
Northern magnetic displacements trigger endogenous fuelling responses in a naive bird migrant
- 2012
-
Ingår i: Behavioral Ecology and Sociobiology. - : Springer Science and Business Media LLC. - 0340-5443 .- 1432-0762. ; 66:5, s. 819-821
-
Tidskriftsartikel (refereegranskat)abstract
- In a previous study, we found that juvenile northern wheatears (Oenanthe oenanthe) exposed to a magnetic displacement to the west of their natural migration route increased their body mass. The total intensity and inclination used for the western displacement may also have been interpreted as northern compared to the experimental site (stronger total field intensity and steeper inclination angle). In order to investigate whether the fuelling response was a response to an unexpected magnetic field or specific to the northern magnetic field, we conducted a new experiment. Juvenile wheatears from the same study population were magnetically displaced to southwestern magnetic fields, exposing the birds to unexpected magnetic combinations, but eliminating the possible effect of a northern magnetic field. A control group was kept in the local geomagnetic field in Sweden for comparison. There was no difference in body mass increase between treatments, suggesting that the fuelling response previously found was not a simple response to an unexpected magnetic field, but rather a specific response to the northern magnetic field. Juvenile wheatears may have developed a fuelling response to northern magnetic fields in order to enable a successful flight towards the migration goal.
|
|
| 6. |
- Boström, Jannika, et al.
(författare)
-
Where on earth can animals use a geomagnetic bi-coordinate map for navigation?
- 2012
-
Ingår i: Ecography. - : Wiley. - 1600-0587 .- 0906-7590. ; 35:11, s. 1039-1047
-
Tidskriftsartikel (refereegranskat)abstract
- Many animal taxa have been shown to possess the ability of true navigation. In this study we investigated the possibilities for geomagnetic bi-coordinate map navigation in different regions of the earth by analysing angular differences between isolines of geomagnetic total intensity and inclination. In no-grid zones where isolines were running almost parallel, efficient geomagnetic bi-coordinate navigation would probably not be feasible. These zones formed four distinct areas with a north-south extension in the northern hemisphere, whereas the pattern in the southern hemisphere was more diffuse. On each side of these zones there was often a mirror effect where identical combinations of the geomagnetic parameters appeared. This may potentially cause problems for species migrating long distances east-west across longitudes, since they may pass areas with identical geomagnetic coordinates. Migration routes assumed for four populations of migratory passerine birds were used to illustrate the possibilities of geomagnetic bi-coordinate map navigation along different routes. We conclude that it is unlikely that animal navigation is universally based on a geomagnetic bi-coordinate map mechanism only, and we predict that the relative importance of geomagnetic coordinate information differs between animals, areas and routes, depending on the different conditions for bi-coordinate geomagnetic navigation in different regions of the earth.
|
|
