Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Accueil du site → Doctorat → Autriche → Causal Analysis of Spatio-Temporal Patterns of Passerine Migration along the Eastern Flyway

Universitaet Innsbruck (2003)

Causal Analysis of Spatio-Temporal Patterns of Passerine Migration along the Eastern Flyway

Yohannes Abrham Elizabeth

Titre : Causal Analysis of Spatio-Temporal Patterns of Passerine Migration along the Eastern Flyway

Auteur : Yohannes Abrham Elizabeth

Akad. Grad : Thesis.Doctoral 2003

Université de soutenance : Universitaet Innsbruck ; Naturwissenschaftliche Fakultaet ; Institut fuer Zoologie und Limnologie

In this dissertation comprehensives picture of autumn and spring migrations of 12 long distance passerine migrants migrating along the eastern migration flyway are presented. Particular emphasis was laid on : 1) To compare body-mass and wing-length variation at successive sites during migration along the flyway ; 2) To investigate the seasonal timing and patterns of age- and sex-related migration differences ; 3) To analyze the temporal patterns of autumn and spring migration in relation to the seasonal rainfall pattern in the eastern Africa region ; 4) To calculate the average autumn and spring migration speeds on the basis of comparisons of median arrival dates at several consecutive stopover sites ; 5) To evaluate the potential use of stable nitrogen (#delta#"15N), carbon (#delta#"13C) and hydrogen (#delta#D) isotope ratios in feathers of migratory birds to help identify the location of autumn stopover sites in northeast Africa. I used migration data from both published and unpublished sources and integrated the studies from northeastern and eastern African ; namely : Sudan, Eritrea, Ethiopia, Uganda, Kenya, and Tanzania. Several migration information from Egypt, Israel, Kuwait, Oman and Saudi Arabia and from countries in the northern hemisphere were integrated into one coherent project within an extensive collaborative framework. The data comprised a total of 263,343 birds in autumn and spring from 107 study sites in autumn and 58 study sites in spring. Most species had a progressive gain in body mass while travelling across Europe before the trans-Saharan flight. There were substantial losses in body mass for all the study species during autumn migration across the desert. Several species showed an increase in body mass in northeastern Africa before migrating to more southerly wintering grounds. During spring migration, marked body-mass increases were observed south of the desert edge before crossing the desert ; mainly further east in the northeastern Africa regions. Several species had a significant body mass loss during their northward migration across the desert. During autumn migration, progressive decreases in wing-length measures were calculated for most of the species investigated. Birds measured at study sites in eastern and northeastern Africa had a greater wing-length variation. The southward migration along the eastern flyway has two stages, interrupted by an extended stopover period. Migrants reach Sudan and Ethiopia between mid-August and early October. The median migration time along eastern equatorial Africa occurs 10 to 12 weeks later. Most birds interrupt migration and spend 1.5 to 3 months at latitudes north of 10°N and 8°N. Spring migration takes a much shorter time. Migration shows a significant difference between age classes, with adults migrating earlier than juveniles. Likewise, sex-related seasonal differential migration patterns revealed that males migrate earlier than females, at least at some stage during migration. In late August and early September, birds arrive in northeast African and stay for 1.5 to 3 months before resuming migration to the south. During these times, localities in the northeastern tropics are drier and resources become available further south. In spring, conditions along the western sector of the route are relatively drier than in autumn, and most birds show a more easterly shifted return passage in spring. Overall, migration in both seasons is well synchronous with the seasonal events of rainfall and changes in the natural environments. It is known that long term environmental information together with short term environmental cues are used to modify endogenous annual rhythms in tropical birds. In such a system, rainfall patterns and associated availability of food resources could function as short-term stimuli to adjust temporal patterns of migration to the changing pattern of weather condition. Generally, migration speeds were significantly higher in spring than in autumn. Unlike in autumn, median migration date had a strong effect on migration speed in spring, in which late migrants migrate faster than early migrants. No significant relationship was observed between body-size measurements and seasonal migration speed. In autumn, birds migrate with a significantly higher speed along the northern latitude migration leg before crossing the desert than in more southerly study sites. Comparisons on the feather #delta#"15N, carbon #delta#"13C and hydrogen #delta#D isotope ratios in feathers of migratory birds to help identify the low values of Marsh Warblers and River Warblers indicate that the two species occupy and grow their feathers in geographic locations with similar stable-isotopic values, in relatively mesic environments, and with higher proportions of C3 (vs.C4) plants. It is evident that during autumn stopover, River Warblers moult their primaries in Ethiopia. It is therefore likely that Marsh Warblers, like River Warblers, stay in Ethiopia and/or in neighboring regions with similar foodweb stable isotope values. Based on feather #delta#D values and regional #delta#D precipitation maps, this region should lie between southeast Sudan and southwest Ethiopia. The relatively enriched #delta#"15N and #delta#"13C values of Whitethroat feathers compared with the two other species reflect the fact that Whitethroats moult in relatively drier environments and/or with a lower proportion of C3 vs. C4 plants. The study showed that Palearctic migrants have well-developed strategies for crossing ecological barriers and of migration in general. Nevertheless, the strategies adopted vary in relation to different environmental conditions, species, age, sex, season, and weather conditions as well as the distance of the destination. The results of the current study add considerable information to the sum of our present knowledge. Understanding the pattern of migration at different locations has important implications for the conservation of migratory species.

Mots clé : Singvoegel Koerpergewicht Fluegellaenge oestliche Palaearktis Vogelzug / Rast / ostafrikanische Flugroute / Herbst Fruehjahr / alters- und geschlechtsspezifische Unterschiede / Niederschlag / Zuggeschwindigkeit Stabile Isotopen Stickstoff / Kohlenstoff / Wasserstoff — passerines / body mass / wing length / eastern Palearctic / bird migration / stopover / eastern Africa flyway autumn spring / age and sex differences / rainfall patterns / migration speed / stable isotopes nitrogen (#delta#"15N) / carbon (#delta#"13C) hydrogen (#delta#D)

Présentation : Österreichische Dissertationsdatenbank

Page publiée le 27 mai 2008, mise à jour le 14 mars 2019