Abstract
Recent technological advancements now allow us to obtain geographical position data for a wide range of animal movements. Here we used light-level geolocators to study the annual migration cycle in great reed warblers (Acrocephalus arundinaceus), a passerine bird breeding in Eurasia and wintering in sub-Saharan Africa. We were specifically interested in seasonal strategies in routes and schedules of migration. We found that the great reed warblers (all males, no females were included) migrated from the Swedish breeding site in early August. After spending up to three weeks at scattered stopover sites in central to south-eastern Europe, they resumed migration and crossed the Mediterranean Sea and Sahara Desert without lengthy stopovers. They then spread out over a large overwintering area and each bird utilised two (or even three) main wintering sites that were spatially separated by a distinct mid-winter movement. Spring migration initiation date differed widely between individuals (1-27 April). Several males took a more westerly route over the Sahara in spring than in autumn, and in general there were fewer long-distance travels and more frequent shorter stopovers, including one in northern Africa, in spring. The shorter stopovers made spring migration on average faster than autumn migration. There was a strong correlation between the spring departure dates from wintering sites and the arrival dates at the breeding ground. All males had a high migration speed in spring despite large variation in departure dates, indicating a time-minimization strategy to achieve an early arrival at the breeding site; the latter being decisive for high reproductive success in great reed warblers. Our results have important implications for the understanding of long-distance migrants’ ability to predict conditions at distant breeding sites and adapt to rapid environmental change.
Highlights
Many species of birds, turtles and sea mammals conduct astonishing long-distance journeys between their breeding and wintering grounds [1]
An interesting example of how harsh environmental conditions during migration can cause substantial delays in breeding was the severe drought in the Horn of Africa in 2011 that affected the timing of the spring migration of several long-distance migrants including geolocator-equipped red-backed shrikes and thrush nightingales (Luscinia luscinia) [7]
Our study provides unique data over the annual migratory cycle of trans-Saharan long-distance migranting great reed warblers equipped with geolocators
Summary
Turtles and sea mammals conduct astonishing long-distance journeys between their breeding and wintering grounds [1]. These impressive migration events have fascinated man for centuries and modern tracking techniques such as GPS-loggers and light-level geolocators are revealing details on route characteristics and migratory behaviours that are revolutionizing our understanding of fundamental aspects of migration [2], [3]. An interesting example of how harsh environmental conditions during migration can cause substantial delays in breeding was the severe drought in the Horn of Africa in 2011 that affected the timing of the spring migration of several long-distance migrants including geolocator-equipped red-backed shrikes and thrush nightingales (Luscinia luscinia) [7]
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