VAN DEN BRINK B & KLAASSEN RHG (2019) Migratory fattening of Barn Swallows Hirundo rustica in the Netherlands. LIMOSA 92 (1): 16-23.

Patterns of fueling for autumn migration of Barn Swallows have been described for different European countries but information from the Netherlands is lacking. Barn Swallows were captured on night roosts near Elburg from July-September, in 1999-2014. Biometry and information on body mass and fat score were collected every 10 days for 10-15 juveniles and 10-15 adult birds and for all ring recoveries. Data from 47 - 254 individuals were collected per year. The total dataset comprised 536 adult males, 592 adult females and 1945 juveniles. Barn Swallows increased in body mass from July through September, males were heavier than females, and adults fueled at a faster rate than juveniles. The increase in body mass could be contributed to the accumulation of fat. Heavy birds with high fat scores (4-5) were rare, even in September when the birds were close to departure. This suggests that Barn Swallows leave the Netherlands with moderate fat scores (2-3), weighing between 18 and 22 g. Such fuel loads are insufficient to migrate directly to tropical Africa, but should enable the swallows to reach southern Europe, where they can refuel. Also in other northern European countries moderate fueling for migration was found.

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