"Is er een verband tussen de traagheid van de rui en de late verschijningsdatum? M.a.w.: zouden dit vogels kunnen zijn van een populatie die laat broedt?"
Waarschijnlijk niet. Dit staat alvast in BWPi.
"By October–November, still mostly in worn juvenile, even when in winter quarters, except for some pale grey feathers with white margins on lower mantle or scapulars (adults at this time of year mostly in non-breeding); abraded upperparts with traces of pale buff fringes, crown black, inner upper wing-coverts fringed pale buff. Later in winter attains full non-breeding (probably except for some inner upper wing-coverts), but further data conflicting: either replaces all juvenile plumage including flight-feathers from mid-winter, and upon arrival in breeding area in 2nd calendar year not distinguishable from adult (Stresemann and Stresemann 1966; Hildén and Vuolanto 1972), or attains none or limited breeding in spring and retains heavily abraded juvenile flight-feathers throughout summer (Prater et al. 1977), usually staying in winter quarters; both probably occur, strategy varying with individual and locality. "
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