But this individual cannot for certain be considered as a proven heuglini as there seems not to be any characters diagnostic for heuglini and even the late primary moult associated with heuglini can even occasionally occur in graelsii as well. The problem of separating graellsii and heuglini is complicated by the recent discovery that graellsii occur occasionally in Finland. This has been proven by the arrival in Finland of birds ringed as pulli in England, the Netherlands and Norway. Thus, only on range it is most likely to be a heuglini.
Features suggesting heuglini in these pictures are upper-parts grey-tone, the state of primary moult and general structure. The bird is obvious paler than typical fuscus and the primary moult has not yet started: P1-P10 still present, but primaries still in relative good condition in June. The primary moult of graellsii and intermedius usually commences in May and continues until November/December whereas heuglini moults later, commencing in June/July and often not being completed until January/February. The general structure, especially slender, long-legged and “elongated” look together with head-shape and bill is often a good clue for heuglini.