We GPS-tracked 19 adult Eleonora’s falcons Falco eleonorae from the westernmost population on the Canary Islands across 39 autumn and 36 spring migrations to and from Madagascar. Furthermore, we sought to disentangle the influence of wind and biome on daily, regional and seasonal travel performance. The Inter-tropical Front (ITF) marks a strong and seasonally shifting climatic boundary at the thermal equator, and we assessed whether migratory detours were associated with this climatic feature. We aimed to determine to what extent a trans-equatorial fly-forage migrant engages in adaptive drift through distinct wind regimes and biomes across Africa. Route choice and travel performance of fly-forage migrants are partly driven by large-scale habitat availability, but it remains unclear to what extent wind support through large-scale wind regimes moulds their migratory behaviour. Asterisks indicate latitudinal bands in which the birds encountered significantly different wind conditions along their migration routes compared to the average conditions within the entire flyway. Wind roses show the frequency of winds depending on speed (colour legend) and the direction towards which winds were blowing. The latter were summarized across the date range and longitudinal range (vertical white dashed lines) used by the birds within each latitudinal band. (c) Wind conditions that birds encountered en route and wind conditions within the rest of the flyway are summarized across consecutive bands of 10° latitude. If the density of hourly locations was higher in orange areas than in green areas within each latitudinal band on each map, then the wind direction that birds encountered was comparable to the wind direction that prevailed within that part of the flyway. The green-orange heatmap represents wind regimes over Western Europe and Africa, showing the relative frequency of westward (U 0, right map) winds thought the flyway during the honey buzzard migration season.
Detours pyreneens code#
All points were coloured for orientation behaviour using the same colour code as in the barplot. (b) We plotted the starting points of all hourly travel segments, on separate maps depending on whether birds experienced a wind with a westward component (left map) or with an eastward component (right map). A high proportion of blues indicates frequent drift and overdrift, while reds signify overcompensation behaviour (legend). (a) Barplot showing the relative frequency of each orientation behaviour and cases with negligible side winds by latitude (binwidth 2°). Geographical flexibility in hourly orientation strategies, wind conditions encountered en route and wind conditions prevailing within the entire flyway during spring migration. 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. 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. They later overdrifted with side winds northwest ward over the Sahel and north-eastward over the Sahara, avoiding adverse winds over the central Sahara.Ĥ. In spring, however, they frequently overcompensated for eastward winds to initiate a westward detour at the start of their journey. 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. Honey Buzzards cross western Africa using different routes in autumn and spring.
We then determined whether winds along the buzzards' detours differed from winds prevailing elsewhere in the flyway.ģ. This enabled us to determine hot spots where buzzards overdrifted and over-compensated for side winds. 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. We tracked 62 migratory journeys of 12 adult European Honey Buzzards Pernis apivorus with GPS loggers. We test this hypothesis by studying orientation behaviour of a long-distance soaring migrant in relation to prevailing winds along the East Atlantic Flyway.Ģ. It is likely some species do this to make the most of predictable wind regimes along their respective flyways. Avian migrants often make substantial detours between their seasonal destinations. NewScript.textContent = script.textContent Var newScript = document.createElement("script")
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