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Fast, vast and variable - spatio-temporal migration patterns of Great Reed Warblers revealed by using geolocators

Lemke, Hilger (2012) BION32 20111
Degree Projects in Biology
Abstract
Abstract:

Avian long-distance migration as an adaptation to spatiotemporally changing resources is a complex evolutionary trait shaped by various endo- and exogenous factors. Descriptive studies of migratory journeys provide direct investigations of migratory parameters and these often set the basis for fun-damental follow-up studies on the eco-evolutionary principles. In this study, male Great Reed War-blers Acrocephalus arundinaceus breeding in south-central Sweden were fitted with geolocators and their individual migration routes, stop-over behaviour and their wintering distribution could be de-termined (6 complete migration tracks there and back and 4 incomplete ones). Furthermore, the timing of movements during both, the migratory... (More)
Abstract:

Avian long-distance migration as an adaptation to spatiotemporally changing resources is a complex evolutionary trait shaped by various endo- and exogenous factors. Descriptive studies of migratory journeys provide direct investigations of migratory parameters and these often set the basis for fun-damental follow-up studies on the eco-evolutionary principles. In this study, male Great Reed War-blers Acrocephalus arundinaceus breeding in south-central Sweden were fitted with geolocators and their individual migration routes, stop-over behaviour and their wintering distribution could be de-termined (6 complete migration tracks there and back and 4 incomplete ones). Furthermore, the timing of movements during both, the migratory and non-breeding season, could be analysed on an individual basis revealing both, striking similarities as well as pronounced variation between individ-uals and seasons. For the first time, the crossing of the Mediterranean Sea and the Sahara desert by a passerine species was successfully tracked. The tracked individuals reached very high ground speeds, which suggest that Great Reed Warblers possibly overfly these barriers without stopping. Season specific patterns of timing and choice of route suggest different selective pressures and envi-ronmental conditions acting on autumn, mid-winter and spring migration, e.g. some individuals but not others flew a longer detour around the Alps during spring. In addition, the geolocation analysis revealed a high variability of calibrated sun angles between individuals, suggesting that Great Reed Warblers use different habitat types or shift behaviour throughout the annual cycle. During the non-breeding season, the tracked birds spread over a vast area including entire West Africa. This portrays an outstanding example for alloheimy, which presumably sets the basis for a complex array of carry-over effects acting on an individual level. These results represent an unexpected diversity within migratory traits in Great Reed Warblers and offer manifold possibilities for follow-up studies dealing with the analysis of proximate and ultimate factors shaping the evolution of long-distance migra-tion.

Popular science summary:

From Sweden to West Africa - the miraculous migration of the Great Reed Warbler

The migration of small songbirds has fascinated people for ages. But due to their small size it has always been difficult to find out more about their journeys and destinations. Right now a new light weighed technology causes a revolution in bird migration studies. This technique allows us - for the first time -to track the migration routes of songbirds!

The ~35g heavy Great Reed Warblers (Acrocephalus arundinaceus) breed in reed beds of shallow and nutrient rich lakes all across Europe up to Central Asia. From a few ring recoveries those birds are known to migrate thousands of kilometres from their breeding sites towards their overwintering grounds, which probably lay in West and South Africa, each year. But which routes do they take? Do they cross the Sahara Desert? In how many days do they reach their wintering site? In order to answer such questions great reed warblers from a lake near Örebro (south central Sweden) have been equipped with advanced light weight geolocators since 2009. After one year we are awaiting the birds returning to their breeding grounds – carrying a geolocator full with exciting data on their back!

Our analyses show that Great Reed Warblers are indeed amazing migrants. They leave their breeding sites almost at the same time during late summer and fly just directly south. North of the Mediterranean Sea the birds make a longer break, where they put on fat reserves for their following long flight. This flight leads across the Mediterranean Sea and the Sahara desert until they reach the Sahel zone just south of the desert. For this flight of roughly 3500km they need on average not more than 6 days of traveling!

Having arrived in Africa the birds spread over a vast area to spend their winter at fixed locations several thousand kilometres apart. The overwintering range of 7 birds ranged covered the entire sub-Saharan West Africa and into Central Africa, from Senegal in the west to Chad in the north, and the Congo basin in the east. This is a remarkable finding since we know now, that these individuals might experience quite different environmental conditions during their non-breeding season. For their spring migration the birds, again, overfly the Sahara with a fast flight. But then they all stop at a rather small area in Algeria and Tunisia. Thus those countries host probably a large proportion of the European great reed warbler population during migration – an important fact for conservation policies. For the future we hope to track individuals repeatedly and see whether they have fixed migration strategies or if they can change their behaviour between years.



Advisor: Bengt Hansson, Dennis Hasselquist, Maja Tarka
Master´s Degree Project,45 ECTS in Animal Ecology 2012
Department of Biology, Lund University. (Less)
Please use this url to cite or link to this publication:
author
Lemke, Hilger
supervisor
organization
course
BION32 20111
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
3632634
date added to LUP
2013-04-10 14:42:43
date last changed
2013-04-10 14:42:43
@misc{3632634,
  abstract     = {Abstract: 

Avian long-distance migration as an adaptation to spatiotemporally changing resources is a complex evolutionary trait shaped by various endo- and exogenous factors. Descriptive studies of migratory journeys provide direct investigations of migratory parameters and these often set the basis for fun-damental follow-up studies on the eco-evolutionary principles. In this study, male Great Reed War-blers Acrocephalus arundinaceus breeding in south-central Sweden were fitted with geolocators and their individual migration routes, stop-over behaviour and their wintering distribution could be de-termined (6 complete migration tracks there and back and 4 incomplete ones). Furthermore, the timing of movements during both, the migratory and non-breeding season, could be analysed on an individual basis revealing both, striking similarities as well as pronounced variation between individ-uals and seasons. For the first time, the crossing of the Mediterranean Sea and the Sahara desert by a passerine species was successfully tracked. The tracked individuals reached very high ground speeds, which suggest that Great Reed Warblers possibly overfly these barriers without stopping. Season specific patterns of timing and choice of route suggest different selective pressures and envi-ronmental conditions acting on autumn, mid-winter and spring migration, e.g. some individuals but not others flew a longer detour around the Alps during spring. In addition, the geolocation analysis revealed a high variability of calibrated sun angles between individuals, suggesting that Great Reed Warblers use different habitat types or shift behaviour throughout the annual cycle. During the non-breeding season, the tracked birds spread over a vast area including entire West Africa. This portrays an outstanding example for alloheimy, which presumably sets the basis for a complex array of carry-over effects acting on an individual level. These results represent an unexpected diversity within migratory traits in Great Reed Warblers and offer manifold possibilities for follow-up studies dealing with the analysis of proximate and ultimate factors shaping the evolution of long-distance migra-tion.

Popular science summary:

From Sweden to West Africa - the miraculous migration of the Great Reed Warbler

The migration of small songbirds has fascinated people for ages. But due to their small size it has always been difficult to find out more about their journeys and destinations. Right now a new light weighed technology causes a revolution in bird migration studies. This technique allows us - for the first time -to track the migration routes of songbirds! 

The ~35g heavy Great Reed Warblers (Acrocephalus arundinaceus) breed in reed beds of shallow and nutrient rich lakes all across Europe up to Central Asia. From a few ring recoveries those birds are known to migrate thousands of kilometres from their breeding sites towards their overwintering grounds, which probably lay in West and South Africa, each year. But which routes do they take? Do they cross the Sahara Desert? In how many days do they reach their wintering site? In order to answer such questions great reed warblers from a lake near Örebro (south central Sweden) have been equipped with advanced light weight geolocators since 2009. After one year we are awaiting the birds returning to their breeding grounds – carrying a geolocator full with exciting data on their back! 

Our analyses show that Great Reed Warblers are indeed amazing migrants. They leave their breeding sites almost at the same time during late summer and fly just directly south. North of the Mediterranean Sea the birds make a longer break, where they put on fat reserves for their following long flight. This flight leads across the Mediterranean Sea and the Sahara desert until they reach the Sahel zone just south of the desert. For this flight of roughly 3500km they need on average not more than 6 days of traveling! 

Having arrived in Africa the birds spread over a vast area to spend their winter at fixed locations several thousand kilometres apart. The overwintering range of 7 birds ranged covered the entire sub-Saharan West Africa and into Central Africa, from Senegal in the west to Chad in the north, and the Congo basin in the east. This is a remarkable finding since we know now, that these individuals might experience quite different environmental conditions during their non-breeding season. For their spring migration the birds, again, overfly the Sahara with a fast flight. But then they all stop at a rather small area in Algeria and Tunisia. Thus those countries host probably a large proportion of the European great reed warbler population during migration – an important fact for conservation policies. For the future we hope to track individuals repeatedly and see whether they have fixed migration strategies or if they can change their behaviour between years. 



Advisor: Bengt Hansson, Dennis Hasselquist, Maja Tarka
Master´s Degree Project,45 ECTS in Animal Ecology 2012 
Department of Biology, Lund University.},
  author       = {Lemke, Hilger},
  language     = {eng},
  note         = {Student Paper},
  title        = {Fast, vast and variable - spatio-temporal migration patterns of Great Reed Warblers revealed by using geolocators},
  year         = {2012},
}