COTTAAR F (2014) Migration phenology, biometry and fattening of Barred Warblers Sylvia nisoria in a Dutch dune area. LIMOSA 87 (4): 203-208.

The Barred Warbler is a scarce to rare migrant in the Netherlands that is regularly trapped at ringing stations in the coastal dunes. At Bird ringing station Cornelis van Lennep near Haarlem, Noord-Holland, the species has been ringed nearly annually since 1985, with a total of 85 birds until 2013, all juveniles. Autumn passage occurred between 7 August (2006) and 9 November (1993), with a peak in late August and early September (eight birds in each 10-day period). In two years exceptional numbers were caught: 18 and 13 birds in 2010 and 2012 respectively. In 2010, only two birds were retrapped, shortly after their first capture, but in 2012 six were retrapped repeatedly until 17 days after their first capture. The recaptures showed that the birds fattened up in the area. The mean body mass increase was 0.59 g/day (SD=0.18, N=6) in birds weighing up to 27 g, and 0.06 g/day (SD=0.03, N=3) in heavier birds. This rate of mass gain (2.4 and 0.3 %/day respectively) was high in comparison to observations made elsewhere and to maximum rates expected from interspecific comparisons. Presumably, the birds profited from the abundant fruiting of European Dewberry Rubus caesius in 2012, as was apparent from their blackish-coloured excreta. These observations show that vagrant Barred Warblers can achieve significant premigratory fattening in the Dutch coastal dunes, at least in favourable years.

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