Autumn migration strategy of juvenile great reed warblers Acrocephalus arundinaceus on the eastern European flyway: a spatiotemporal pattern of accumulation and utilisation of energy stores (original) (raw)
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Journal of Ornithology, 2008
To investigate migratory connectivity in the Reed Warbler Acrocephalus scirpaceus, we analysed (1) all available sub-Saharan ringing recoveries and (2) stable isotopes in feathers grown in Africa sampled at 17 European breeding sites across a migratory divide. A cluster analysis of ringing recoveries showed remarkable connectivity between breeding and non-breeding grounds. Two main clusters represented populations taking the two main migratory routes [southwesterly (SW) and southeasterly (SE)]. Stable isotope analysis confirmed the separation of wintering areas of SW-and SE-migrating populations. Higher d 15 N values in feathers of SE-migrating birds indicated that they occupied more xeric biome types. Values of d 13 C that did not differ significantly among populations were higher than those from feathers of known European origin and indicated a C4 biome. Three populations with an unknown migratory direction were assigned to the SE-migrating populations on the basis of d 15 N values.
Conditions at autumn stopover sites affect survival of a migratory passerine
Journal of Ornithology, 2017
Weather is an important factor affecting many aspects of avian ecology, yet its importance for survival during various periods of the avian annual cycle has received relatively little attention and remains poorly understood. We have investigated the effect of weather conditions at the breeding and wintering grounds and during migration on the survival probability of Eurasian Reed Warblers Acrocephalus scirpaceus, a long-distance Palaearctic-African migrant species. We found that annual survival was significantly affected by precipitation at the autumn stopover sites in Spain and Morocco, where Reed Warblers accumulate energy reserves prior to crossing the Sahara desert: low rainfall was associated with decreased survival. We suggest that arid conditions at these crucial stopover sites may cause limitations in food availability, prevent proper refueling and hence result in lower survival. Survival estimates were not related to weather conditions in Africa during the bird wintering period or the preceding wet season. Likewise, meteorological conditions at the breeding area did not influence survival. Survival estimates for males and females did not differ, although recapture probability was significantly lower for females than for males. Our results indicate that weather significantly influences Reed Warbler survival, although its effect may vary for different stages of the annual cycle. Our findings suggest that marked climatic changes occurring along migratory routes, in particular at important stopover sites, may have far-reaching consequences on bird survival and population size. Keywords Annual survival Á Meteorological conditions Á Weather Á Migration Á Eurasian Reed Warbler (Acrocephalus scirpaceus) Á Climate change Zusammenfassung Die Bedingungen an den Herbstrastplätzen beeinflussen das Ü berleben eines ziehenden Singvogels Das Wetter ist ein wichtiger Faktor, der bei Vögeln viele Aspekte der Ö kologie beeinflusst; dennoch wurde seiner Bedeutung für das Ü berleben während verschiedener Phasen des jährlichen Zyklus der Vögel relativ wenig Aufmerksamkeit zuteil und man weiß nach wie vor nur wenig darüber. Wir untersuchten die Auswirkungen der Wetterbedingungen in den Brut-und Ü berwinterungsgebieten sowie auf dem Zugweg auf die Ü berlebenswahrscheinlichkeit von Teichrohrsängern Acrocephalus scirpaceus, Langstreckenziehern zwischen Paläarktis und Afrika. Die jährlichen Ü berlebensraten wurden signifikant von den Niederschlagsmengen in den Herbstrastgebieten in Spanien und Marokko beeinflusst, wo Communicated by F. Bairlein.
Scientific reports, 2017
Long-distance migratory organisms are under strong selection to migrate quickly. Stopovers demand more time than flying and are used by individuals to refuel during migration, but the effect of fuel loads (fat) acquired at stopover sites on the subsequent pace of migration has not been quantified. We studied stopover behaviour of Grey-cheeked Thrush (Catharus minimus) at a site in northern Colombia and then tracked their migration using an intercontinental radio-telemetry array. Tracking confirmed long-distance flights of more than 3000 km, highlighting the key importance of a single stopover site to the migration strategy of this species. Our results suggest that these songbirds behave as time-minimizers as predicted by optimal migration theory, and that fuel loads acquired at this South American stopover site, together with departure date, carry-over to influence the pace of migration, contributing to differences in travel time of up to 30 days in birds subsequently detected in th...
Journal of Animal Ecology, 2019
It is essential to gain knowledge about the causes and extent of migratory connectivity between stationary periods of migrants to further the understanding of processes affecting populations, and to allow efficient implementation of conservation efforts throughout the annual cycle. Avian migrants likely use optimal routes with respect to mode of locomotion, orientation and migration strategy, influenced by external factors such as wind and topography. In self‐powered flapping flying birds, any increases in fuel loads are associated with added flight costs. Energy‐minimizing migrants are therefore predicted to trade‐off extended detours against reduced travel across ecological barriers with no or limited foraging opportunities. Here, we quantify the extent of detours taken by different populations of European nightjars Caprimulgus europaeus, to test our predictions that they used routes beneficial according to energetic principles and evaluate the effect of route shape on seasonal mi...
Migratory connectivity and population-specific migration routes in a long-distance migratory bird
Proceedings of the Royal Society B: Biological Sciences, 2014
Knowledge about migratory connectivity, the degree to which individuals from the same breeding site migrate to the same wintering site, is essential to understand processes affecting populations of migrants throughout the annual cycle. Here, we study the migration system of a long-distance migratory bird, the Montagu's harrier Circus pygargus, by tracking individuals from different breeding populations throughout northern Europe. We identified three main migration routes towards wintering areas in sub-Saharan Africa. Wintering areas and migration routes of different breeding populations overlapped, a pattern best described by 'weak (diffuse) connectivity'. Migratory performance, i.e. timing, duration, distance and speed of migration, was surprisingly similar for the three routes despite differences in habitat characteristics. This study provides, to our knowledge, a first comprehensive overview of the migration system of a Palaearctic-African long-distance migrant. We emphasize the importance of spatial scale (e.g. distances between breeding populations) in defining patterns of connectivity and suggest that knowledge about fundamental aspects determining distribution patterns, such as the among-individual variation in mean migration directions, is required to ultimately understand migratory connectivity. Furthermore, we stress that for conservation purposes it is pivotal to consider wintering areas as well as migration routes and in particular stopover sites.
Ibis, 2011
The Sahara desert acts as an ecological barrier for billions of passerine birds on their way to and from their African wintering areas. The Garden Warbler Sylvia borin is one of the most common migrants involved. We used body mass of this species from Greece in autumn and spring to simulate the desert crossing and to assess how body mass relates to fuel requirement. The flight range estimates were adjusted to the seasonal extent of the desert, 2200 km in autumn and about 2800 km in spring. In autumn, with an average fuel load of about 100% of body mass without fuel, birds were not able to cross the desert in still air, but northerly winds prevail during September and with the average wind assistance only one in 14 was predicted to fail to make the crossing. Body mass data from spring, after the desert crossing, was used to estimate departure body mass from south of the desert. The average wind assistance in spring is close to zero and departure body mass of the average bird arriving at Antikythira, a small Greek island, under such conditions was estimated to be 34.6 g, which corresponded to a fuel load of 116%. Calculations based on 1% body mass loss per hour of flight showed slightly larger body mass loss than that calculated from flight range estimates. The results suggest that passerine birds about to cross the eastern part of the Sahara desert need to attain a larger fuel load in spring than in autumn.
Animal Migration
Hundreds of millions of birds reach the Mediterranean islands or Mediterranean coast of Europe every spring after having crossed the Sahara Desert and the Mediterranean Sea. Using data from three small insular stopover sites, we calculated body mass without fuel for 18 trans-Saharan passerine migrants. We subsequently used arrival fuel loads coupled with potential flight range estimates to assess the percentage of birds that are forced to perform an obligatory stopover after crossing the Mediterranean Sea due to fuel depletion. Average arrival fuel loads were among the lowest ever recorded in the Mediterranean region and minimum body mass values recorded for several species were lower than any other individual value reported. The percentage of birds that needed to replenish their energy stores before resuming their northward migration journey varied from 0% to 50% depending on the species and locality studied. Based on conservative estimates at least 180 million birds of our study s...
Seasonal detours by soaring migrants shaped by wind regimes along the East Atlantic Flyway
1. Avian migrants often make substantial detours between their seasonal destinations. It is likely some species do this to make the most of predictable wind regimes along their respective flyways. We test this hypothesis by studying orientation behaviour of a long-distance soaring migrant in relation to prevailing winds along the East Atlantic Flyway. 2. We tracked 62 migratory journeys of 12 adult European Honey Buzzards Pernis apivorus with GPS loggers. Hourly fixes were annotated with local wind vectors from a global atmospheric model to determine orientation behaviours with respect to the buzzards' seasonal goal destinations. This enabled us to determine hot spots where buzzards overdrifted and over-compensated for side winds. We then determined whether winds along the buzzards' detours differed from winds prevailing elsewhere in the flyway. 3. Honey Buzzards cross western Africa using different routes in autumn and spring. In autumn, they overcompensated for westward winds to circumvent the Atlas Mountains on the eastern side and then overdrifted with south-westward winds while crossing the Sahara. In spring, however, they frequently overcompensated for eastward winds to initiate a westward detour at the start of their journey. They later overdrifted with side winds northwest ward over the Sahel and north-eastward over the Sahara, avoiding adverse winds over the central Sahara. 4. We conclude that Honey Buzzards make seasonal detours to utilize more supportive winds further en route and thereby expend less energy while crossing the desert. Lifelong tracking studies will be helpful to elucidate how honey buzzards and other migrants learn complex routes to exploit atmospheric circulation patterns from local to synoptic scales.