VAN NOORDEN B, JANSSEN R & VAN HORSSEN P (2022) The Odyssee of the Icterine Warbler Hippolais icterina: migration routes and wintering areas of a long-distance migrant. LIMOSA 95 (2): 67-79.

Relatively little is known about the migration routes of Icterine Warblers. Ringing data (EURING) provide a fairly good idea of the migration within Europe (Fig. 3), but only eleven recoveries from the African continent are known, six of which are south of the Sahara (Fig. 2). Field observations indicate wintering in Southern Africa (Fig. 1).
To determine where Dutch Icterine Warblers winter and how they get there, we deployed light-level geolocators on 15 individuals, of which two returned and were recaptured (a male and female) in the subsequent year. The total outward and return journey has been recorded for both birds. The birds showed similar migratory patterns, with some minor differences (Fig. 4). The male started autumn migration around August 1 and arrived 5 days later in southern Italy to make a 30-day stopover. From September 7, the bird moved further south although we could not follow the last part of this migration leg because of positioning problems due to equinox. The female stayed for a much longer time in or near the breeding area and only left around 1 September in a south-easterly direction, to arrive along the Croatian coast on 7 September. On October 7, when positions could be calculated again after the equinox, both birds had already arrived in Southern Africa. The male stayed for 149 days in the north of Namibia and the female for 145 days along the Namibian coast, around the border with Angola.
Early March, both birds started spring migration. Due to equinox, no positions could be estimated until April 3, when the male was in northern Angola and the female in southern Cameroon. Here the birds made stopovers of 7 and 38 days, respectively. The male continued to the border area between Nigeria and Benin and the female to Burkina Faso where both birds stopped once more before crossing the Sahara. They arrived in the Mediterranean at the end of April, to arrive in the breeding area at 10 and 13 May (Fig. 5).
The migration speed (including stopovers) of the male was lower in autumn (139 km/day) than in spring (183 km/day). Both birds probably flew non-stop during several days (32-56 hours) when crossing the Sahara in spring, whereas no indications for nonstop flights were found for autumn migration.

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