Abstract:This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.
“…Despite regional variations in travel time budgets, realized tailwinds had a strong positive effect on daily mean travel speeds in both seasons, and models accounting for the combined effect of travel time and tailwind accounted for more than 60% of variation in daily travel distances, whereby the seasonal difference in realized wind support explains the marked seasonal difference in travel performance. Therefore, the faster spring travel is not evidence of a time-minimizing strategy, but rather a result of favourable seasonal conditions [ 59 ], whereby the late breeding and long pre-breeding period of Eleonora’s falcons likely buffers selection for time-minimization and early arrival to the summer range [ 36 , 39 ].…”
Section: Discussionmentioning
confidence: 99%
“…1 a). The Eleonora’s falcon colony on Alegranza consists of an average of 127 breeding pairs, about 45% of the Canarian breeding population [ 36 , 37 ], and is located at the western limit of the species’ breeding range. Fig.…”
Background
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. 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. 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. Furthermore, we sought to disentangle the influence of wind and biome on daily, regional and seasonal travel performance.
Methods
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. Tracks were annotated with wind data to assess the falcons’ orientation behaviour and the wind support they achieved in each season and distinct biomes. We further tested whether falcon routes across the Sahel were correlated with the ITF position, and how realized wind support and biome affect daily travel times, distances and speeds.
Results
Changes in orientation behaviour across Africa’s biomes were associated with changes in prevailing wind fields. Falcons realized higher wind support along their detours than was available along the shortest possible route by drifting through adverse autumn wind fields, but compromised wind support while detouring through supportive spring wind fields. Movements across the Sahel-Sudan zone were strongly associated to the ITF position in autumn, but were more individually variable in spring. Realized wind support was an important driver of daily travel speeds and distances, in conjunction with regional wind-independent variation in daily travel time budgets.
Conclusions
Although daily travel time budgets of falcons vary independently from wind, their daily travel performance is strongly affected by orientation-dependent wind support. Falcons thereby tend to drift to minimize or avoid headwinds through opposing wind fields and over ecological barriers, while compensating through weak or supportive wind fields and over hospitable biomes. The ITF may offer a climatic leading line to fly-forage migrants in terms of both flight and foraging conditions.
“…Despite regional variations in travel time budgets, realized tailwinds had a strong positive effect on daily mean travel speeds in both seasons, and models accounting for the combined effect of travel time and tailwind accounted for more than 60% of variation in daily travel distances, whereby the seasonal difference in realized wind support explains the marked seasonal difference in travel performance. Therefore, the faster spring travel is not evidence of a time-minimizing strategy, but rather a result of favourable seasonal conditions [ 59 ], whereby the late breeding and long pre-breeding period of Eleonora’s falcons likely buffers selection for time-minimization and early arrival to the summer range [ 36 , 39 ].…”
Section: Discussionmentioning
confidence: 99%
“…1 a). The Eleonora’s falcon colony on Alegranza consists of an average of 127 breeding pairs, about 45% of the Canarian breeding population [ 36 , 37 ], and is located at the western limit of the species’ breeding range. Fig.…”
Background
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. 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. 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. Furthermore, we sought to disentangle the influence of wind and biome on daily, regional and seasonal travel performance.
Methods
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. Tracks were annotated with wind data to assess the falcons’ orientation behaviour and the wind support they achieved in each season and distinct biomes. We further tested whether falcon routes across the Sahel were correlated with the ITF position, and how realized wind support and biome affect daily travel times, distances and speeds.
Results
Changes in orientation behaviour across Africa’s biomes were associated with changes in prevailing wind fields. Falcons realized higher wind support along their detours than was available along the shortest possible route by drifting through adverse autumn wind fields, but compromised wind support while detouring through supportive spring wind fields. Movements across the Sahel-Sudan zone were strongly associated to the ITF position in autumn, but were more individually variable in spring. Realized wind support was an important driver of daily travel speeds and distances, in conjunction with regional wind-independent variation in daily travel time budgets.
Conclusions
Although daily travel time budgets of falcons vary independently from wind, their daily travel performance is strongly affected by orientation-dependent wind support. Falcons thereby tend to drift to minimize or avoid headwinds through opposing wind fields and over ecological barriers, while compensating through weak or supportive wind fields and over hospitable biomes. The ITF may offer a climatic leading line to fly-forage migrants in terms of both flight and foraging conditions.
“…Similar findings were reported by Mellone et al (2012b) for two tracked female falcons from a colony in Morocco for the period between the 3 rd week of September until the onset of autumn migration one month later, reporting the largest trip ever recorded of 181 km, in accordance with our findings. Previous estimates, based on the duration of hunting excursions of male Eleonora's Falcons from a colony in Sardinia (Italy), suggest that an average straight-line trip would be 24 km from the colony (Rosén et al 1999), however foraging trips of up to 140 km have been recently recorded for GPS-tracked males in the Canary Islands (Gangoso et al 2020). Male falcons are mainly responsible for food provision, i.e.…”
Section: Breeding Periodmentioning
confidence: 99%
“…To sum up, based on our findings and considering the high mobility of Eleonora's Falcon while at its breeding grounds, tracking technology is undoubtedly an asset for the study of the species' movement ecology and consequently, its conservation. We therefore highly recommend the continuation of tracking studies to collect high precision relocation and environmental data from animal-borne sensors, of even finer sampling frequency, from other colonies as well as from male Eleonora's Falcons to account for inter-individual, sex-and site-related variability, as recently implemented in the Canary Islands (Gangoso et al 2020). Taking into account the increasing demand for renewable energy investments, especially in wind energy, information on the 3D space use regarding both the breeding and pre-breeding period could guide decisions on the installation of wind farms in continental and insular environments, as well as in offshore areas in Greece.…”
Section: Pre-breeding Periodmentioning
confidence: 99%
“…Still, to date the movement ecology of the species during the pre-breeding and breeding period remains largely unexplored. Indeed, there have been only three satellite telemetry studies up to now: Mellone et al (2013a) and Gangoso et al (2020) in Spain and Mellone et al (2012b) in Morocco. Despite the small sample size of the tracked falcons and the rather large sampling interval owing to technical limitations of the equipment available in earlier years, telemetry studies have provided the first evidence of site fidelity, reported on the land cover composition where the species occurred during the pre-breeding period (Mellone 2013a), and revealed important information on the ranging behaviour of the species during the breeding period, highlighting the importance of inland areas for foraging (Mellone 2012b).…”
Summary
Eleonora’s Falcon Falco eleonorae is a migratory raptor, well-known for its delayed breeding period. Owing to its great mobility, current information on its distribution pattern during the pre-breeding period is rather sporadic, mainly based on field observations and only one telemetry study. Likewise, the species’ ranging activity during the breeding period has not been thoroughly investigated due to methodological limitations of the approaches implemented in previous studies, again amounting to only two telemetry studies in recent years. In this study we aimed to provide a comprehensive overview of the species’ ranging activity at its breeding grounds based on telemetry. Utilizing GPS data from six adult females originating from the core of the species’ breeding range we explored broad- and fine-scale activity patterns while at their breeding grounds. Our results indicated that during the pre-breeding period the falcons visited high biodiversity areas lying hundreds of kilometres away from their colonies, exhibiting site-fidelity, as shown for falcons from other breeding colonies in the past. During the breeding period the falcons roamed at an average distance of 17 km from their nesting sites, but their ranging activity could be observed up to 130 km. In accordance with the species’ breeding biology, the falcons tended to perform longer trips as the nestlings became more independent. The temporal pattern of ranging activity fitted well with the diurnal variability of the autumn migration flux. Furthermore, nest attendance tended to decrease in windy conditions and as the season progressed, and to increase when southerly winds blew. Despite the low number of tracked falcons, our study set a reference basis for future studies highlighting the importance of specific (protected) areas during the pre-breeding period and providing the first assessment of the movement ecology of the species during the pre-breeding and breeding period in Greece.
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