DOI: 10.5061/dryad.1rn8pk0zp
title: A trans-African migrant shows repeatable route choice in males and repeatable timing in females

description: Migrant bird populations often show substantial variation in route choice
 and timing. Determining whether this population-level variation is driven
 by between-individual differences and/or flexibility within individuals is
 key to identifying drivers of migration patterns. ‘Repeatability’ (R, the
 proportion of population-level variation attributable to
 between-individual variation) has become a central metric for the relative
 consistency of individual behaviour. Individual repeatability in migratory
 route choice and timing is often reported to vary between seasonal and
 regional contexts and may also differ between demographic groups (e.g.
 sexes), but interpreting repeatability requires careful consideration of
 the underlying changes in between- and within-individual variation. We
 GPS-tracked repeat migrations for eight male and five female Eleonora’s
 falcons Falco eleonorae and quantified the magnitude of within- and
 between-individual variation and the individual repeatability of their
 seasonal routes and timing at 100km intervals all across Africa. We did
 this across both sexes and then separately for males and females. We found
 greater between-individual variation in spring routes, albeit with
 substantial regional fluctuations in both seasons. The greatest
 between-individual variation in routes occurred during the spring
 desert-crossing, but this coincided with high within-individual variation,
 and thus only low repeatability of route choice. Route repeatability
 instead peaked (R = 0.6–0.8) through the Horn of Africa in spring and
 during the rainforest-crossing in autumn. Variation and repeatability of
 timing were stable across regions, with generally higher
 between-individual variation and repeatability in spring. Sex-specific
 analyses suggest males exhibit higher route repeatability, while females
 exhibit stronger seasonal contrasts in timing repeatability. Such sex
 differences were unexpected, but overall, between-individual variation and
 repeatability in routes and timings appear greater where environmental and
 annual cycle constraints are weaker. Route repeatability is especially
 high where falcons show fidelity to stop-over sites, or individual
 barrier-crossing preferences. Individual routines may be acquired through
 early-life exploration-refinement.
description: <em><strong>Tracking
 falcons</strong></em> Since
 2012 we have tagged 40 Eleonora’s falcons with UvA-BiTS GPS-trackers
 (7.5g, www.uva-bits.nl,
 Bouten et al. 2013) on Alegranza Islet (29°24'N, 13°30'W,
 1050 ha, max 289 m a.s.l.). GPS-trackers were attached using a
 backpack-style harness made from 6.35 mm wide Teflon. Device and harness
 weighed ~8 g, corresponding to max. 2.63% and 2.42% of the mass at capture
 for males (min. 304g) and females (min. 330g), respectively. Data was
 downloaded locally through a custom-built antenna network, and up until
 the summer of 2020 we retrieved data for 19 falcons, and repeated tracks
 for 13 of these, Further details on return rates and apparent survival are
 provided in Vansteelant et al. (2021). All birds were sexed using
 molecular methods (see Gangoso & Figuerola,
 2019, for further
 details).
 Falcon trapping and tagging were approved by the Dirección
 General de Protección de la Naturaleza (Viceconsejería de Medio Ambiente),
 Canarian Government (permits n° 2014/2224, 2015/3835, 2017/6829,
 2020/10521). <strong>Processing migration
 data</strong> Because
 tracking data were collected at variable time intervals (depending on e.g.
 dynamic measurement schemes, battery power) we resampled individual tracks
 to hourly intervals prior to further analyses. Next, we identified the
 start and end date of each migration trip based on a combination of daily
 movement statistics and geographical criteria. We first calculated the
 great-circle distance between the first to the last fix on each bird-day
 and classified days on which falcons covered a distance &gt;100km as
 travel days. Days on which falcons covered shorter distances were
 considered as ‘stationary’ days. Tracks were then partitioned into
 ‘travel’ and ‘stationary’ segments, and we defined the end of autumn and
 the start of spring migration as the first and last day, respectively, on
 which falcons remained stationary for at least three days in Madagascar.
 Determining the start of autumn and the end of spring migration is more
 complicated because falcons spend up to two months at pre-breeding sites
 on mainland NW Africa before returning to the colony to breed. Because the
 focus of this study is on repeatability of directed long-distance
 movements, we considered that spring migration ended on the first day that
 falcons either reached the Atlantic Ocean or stopped-over in Morocco or
 the Western Sahara. Finally, we considered that autumn migration started
 on the day that falcons last visited the colony, thus including short
 stop-overs in NW Africa prior to the desert-crossing in the autumn
 migration.<br> <strong>Literature
 cited</strong> Bouten, W.,
 Baaij, E.W., Shamoun-Baranes, J. <em>et al.</em>
 <strong>2013</strong> A flexible GPS tracking system for
 studying bird behaviour at multiple scales. <em>J
 Ornithol</em> <strong>154</strong>, 571–580. https://doi.org/10.1007/s10336-012-0908-1 Gangoso L, Figuerola J. <strong>2019</strong>. Breeding success but not mate choice is phenotype- and context-dependent in a color polymorphic raptor. Behav Ecol 30(3):763-769. doi: 10.1093/beheco/arz013.
description: This tracking dataset can be processed using the R code provided
 at the GitHub repository of Wouter Vansteelant: https://github.com/Wouter-Vansteelant/Vansteelant-etal-2023-JAvianBiol The repository contains all the code necessary to replicate our analyses and includes links to third-party online accessible datasets that were used for visualizing and analysing the data.