van Oordt G.J. (1950) Is de Pestvogel (Bombycilla garrulus) een echte trekvogel? ARDEA 37 (3-4): 179-181

During the winters 1946/47, 1948/49 en 1949/50 a small flock of Waxwings (Bombycilla garrulus) was observed at Bilthoven (near Utrecht), where the birds each year, showing exactly the same behaviour, nearly always inhabited the same garden and its near surroundings. It is concluded that the flock always consisted of the same individuals. Therefore these birds must have followed the same route from their breeding range to their winter-quarter. Consequently, the Waxwing is not a species, which leaves its breeding area in different directions, but in a de fin it e direction; hence it must be considered a true migrant.