Timing of nocturnal passerine migration in Arctic light conditions
Author
Summary, in English
The nocturnal migration of many passerines
starts after sunset and reaches peak intensity during the dark
hours of the night. Birds destined for high Arctic breeding
grounds encounter a special situation, as they will experience
continuous daylight when reaching the high latitudes during
the final part of spring migration. How does this affect the
pattern of nocturnal migration? We consider three alternative
hypotheses; that the period of nocturnal flight activity
may become compressed, remain unchanged or become
disorganized under Arctic light conditions. We tracked migrating
birds by radar north of the Arctic Circle (at Abisko,
68210N, 18490E, in Swedish Lapland) and show that the
pattern during the night, with a migration peak around
midnight, persisted even in continuous daylight when the sun
remained above the horizon throughout the 24 h of the day.
The flight intensity peak under continuous daylight in spring
(midnight sun) was very similar to the corresponding peak in
autumn, when the migration took place under twilight conditions.
The duration of the flight period under continuous
daylight in spring lasted 8–10 h and did not seem to be
compressed. We hypothesize that the flight period under
midnight sun conditions may in fact be more protracted than
during short nights, because of release from twilight cues that
tend to synchronize initiation and termination of migratory
flights. These cues will thus capture and confine the flight
period. The results of this provisional study suggest interesting
dynamics in timing of nocturnal migratory flights
under seasonally and latitudinally changing day length
conditions, which will need detailed documentation by future
studies of migration intensity at high-latitude sites.
starts after sunset and reaches peak intensity during the dark
hours of the night. Birds destined for high Arctic breeding
grounds encounter a special situation, as they will experience
continuous daylight when reaching the high latitudes during
the final part of spring migration. How does this affect the
pattern of nocturnal migration? We consider three alternative
hypotheses; that the period of nocturnal flight activity
may become compressed, remain unchanged or become
disorganized under Arctic light conditions. We tracked migrating
birds by radar north of the Arctic Circle (at Abisko,
68210N, 18490E, in Swedish Lapland) and show that the
pattern during the night, with a migration peak around
midnight, persisted even in continuous daylight when the sun
remained above the horizon throughout the 24 h of the day.
The flight intensity peak under continuous daylight in spring
(midnight sun) was very similar to the corresponding peak in
autumn, when the migration took place under twilight conditions.
The duration of the flight period under continuous
daylight in spring lasted 8–10 h and did not seem to be
compressed. We hypothesize that the flight period under
midnight sun conditions may in fact be more protracted than
during short nights, because of release from twilight cues that
tend to synchronize initiation and termination of migratory
flights. These cues will thus capture and confine the flight
period. The results of this provisional study suggest interesting
dynamics in timing of nocturnal migratory flights
under seasonally and latitudinally changing day length
conditions, which will need detailed documentation by future
studies of migration intensity at high-latitude sites.
Department/s
Publishing year
2015
Language
English
Pages
1453-1459
Publication/Series
Polar Biology
Volume
38
Issue
9
Document type
Journal article
Publisher
Springer
Topic
- Ecology
Status
Published
ISBN/ISSN/Other
- ISSN: 1432-2056