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Orientation
Birds seem to have a sixth sense to
find their way on the wide-ranging journeys. Intensive
research during the two recent decades has expanded
knowledge about birds' compass mechanisms greatly, and it
has been demonstrated that they rely on several different
cues - the geomagnetic field, sun, sunset, skylight
polarization pattern and stars - for their orientation.
Still, we have little understanding how they actually
orient when traveling on migration, what is the relative
importance of different cues in the birds' orientation
systems, and how the different compass mechanisms
interact.
Our research is focused on the
ecological aspects of bird orientation, and we try to
find out if birds adapt their orientation and use of
different cues depending on their fuel condition and
migratory situation. We have indeed demonstrated a
profound difference in orientation behaviour between fat
and lean birds captured on migration. We have also
carried out extensive orientation cage experiments with
manipulations of the magnetic field, sky visibility and
skylight polarization, comparing the responses of
different species. Such experiments have been conducted
close to the Magnetic North Pole in arctic Canada, in
Greenland, at the northern tundra in Siberia and close to
the equator in Kenya, to investigate how birds cope with
the special difficulties of orientation at these places.
We have a close collaboration with the bird observatories
at
Falsterbo and
Ottenby for our
orientation research programme in Sweden. In addition to
cage experiments, release experiments, radio telemetry,
as well as radar and satellite tracking are recurrent
methods in our orientation research.
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Current studies include experiments
on the light dependent magnetic orientation in birds and
radar studies on free flying birds.
Successful modifications of the orientation cage
technique open up long-awaited possibilities of comparing
the orientation responses of waders with existing results
for many passerine species. Other ongoing experiments
deal with the intercalibration of different compass
mechanisms during the birds' ontogeny, and with the
importance of the wavelength of monochromatic light for
the orientation capacity with and without access to the
normal geomagnetic field.
Quite another type of approach is to
examine travel routes and flight paths (as recorded by
radar and satellite tracking) in the light of various
predictions, based on different possible orientation
mechanisms, about courses and course changes. Flight
routes are particularly revealing in polar regions where
the birds meet special difficulties in orientation and
where great circle orientation is of highest significance
(see also
migration patterns ).
Preliminary results, which indicate that waders in
northernmost Siberia may orient close to great circle
routes while this is not the case for brent geese flying
across Greenland, inspire to continued investigations.
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Primary projects: Susanne Åkesson, Thomas Alerstam
Graduate programmes: Oskar Brattström, Johanna Grönroos
Other researchers: Johan Bäckman, Rachel Muheim, Kasper Thorup
A few selected publications:
- Åkesson, S. & Hedenström, A.
Selective flight departure in passerine nocturnal migrants.
- Behav. Ecol. Sociobiol. 47:140-144.
- Åkesson, S., Morin, J.,
Muheim, R. & Ottosson, U. 2001. Avian
orientation at steep angles of inclination: experiments
with migratory white-crowned sparrows at the magnetic
North Pole. - Proc. R. Soc. Lond. B. 268:1907-1913.
- Alerstam, T. 1996.
The geographic scale factor in orientation of migrating
birds. - J. Exp. Biol. 199:9-19.
- Bäckman, J. & Alerstam, T.
2001. Confronting the winds: orientation and flight
behaviour of roosting swifts, Apus apus.
- Proc. R. Soc. Lond. B 268:1081-1087.
- Luschi, P., Åkesson, S., Broderick,
A. C., Glen, F., Godley, B. J., Papi, F. & Hays, G. C.
2001. Testing the navigational abilities of ocean migrants:
displacement experiments on green turtles (Chelonia mydas).
- Behav. Ecol. Sociobiol. 50:528-534.
- Sandberg, R., Bäckman, J., Moore,
F. R. & Lohmus, M. 2000. Magnetic orientation
calibrates celestial cues during migration. - Anim. Behav. 60:453-462.
- Thorup, K., Alerstam, T., Hake, M. &
Kjellén, N. 2003. Bird orientation: compensation for wind
drift in migrating raptors is age-dependent. - (Biology Letters) Proc. R. Soc.
Lond. B (suppl) 270:S8-S11.
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