Abstract
The migration strategies of smaller, south European, Mediterranean birds are less well known than those of northern and central European birds. We used geolocators to map individual spatiotemporal migration schedules of three species breeding in the Iberian Peninsula: the White-rumped Swift Apus caffer, rufous-tailed Scrub-robin Cercotrichas galactotes and Bluethroat Cyanecula svecica. The three species crossed the Sahara desert with a westward detour, to reach West African winter grounds in the Sahel (Bluethroats and Scrub-robins) or the rainforest belt (Swifts). Despite the proximity of the breeding grounds to the desert barrier, all but one individual stopped over before the desert crossing during autumn migration. After spending six months on average in sub-Saharan Africa with variable itinerancy, spring migration was faster overall and more direct than in autumn. Autumn migration was of similar duration to that found in related northern European migrants and therefore slower in southern birds. Spring migration was completed in less time than in the northern migrants (data only for Swifts and Scrub-robins). The shorter migration distance and proximity to the barrier potentially allow south European trans-Saharan migrants to migrate more slowly than northern migrants but only when less time-constrained in autumn.—Lomas vega, M., Willemoes, M., Arizaga, J., Onrubia, A., Cuenca, D., Alonso, D., Torralvo, C., Tottrup, A.P. & Thorup, K. (2019). Migration strategies of Iberian breeding White-rumped Swifts Apus caffer, rufous-tailed Scrub-robins Cercotrichas galactotes and Bluethroats Cyanecula svecica. Ardeola, 66: 51-64.
Highlights
Timing of migration is largely determined by breeding latitude, presumably because climatic conditions limit food resources towards the North (Holmes, 1971; Conklin et al, 2010; Briedis et al, 2016)
We used geolocators to map the spatiotemporal schedule of three southern European, long-distance migrants: Whiterumped Swift Apus caffer, rufous-tailed Scrub-robin Cercotrichas galactotes and Bluethroat Cyanecula svecica, from breeding sites in the Iberian Peninsula
Because migration often occurs close to the equinox, when latitude estimation using geolocators is impossible, we restricted our identification of spatiotemporal migration-strategy measures to (1) timing of arrival and departure on breeding and winter grounds, (2) stopovers before barrier crossing, (3) detours when crossing the barrier, (4) duration, distance and speed of spring and autumn migration, and (5) itinerancy during winter
Summary
Adult males and first-year birds of the southern species were fitted with archival light-level loggers (geolocators) on breeding grounds in central and southern Spain. The return rates of birds fitted with geolocators were 0.16 for Swifts, 0.20 for adult and 0 for first-year Scrub-robins, and 0.12 for Bluethroats. No control sample was available for the Bluethroats For another Spanish population, the return rate ranged from 0.05-0.3, depending on year, site and sampling effort (Arizaga & García, 2013). One set of the Bluethroat light data was only used for timing of migration analysis since the migration periods were well defined but the location estimates were highly imprecise, possibly due to a high degree of shading. Another Bluethroat logger did not record data. Due to high variability in the light data, especially at the end of the battery life, it was not possible to determine the number of stationary winter periods and wintering duration for Bluethroats and one Swift (Supplementary material, Figures S1– S3)
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