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For heuglini, the most detailed analysis is probably by Buzun, published in BB. Last March, in Scotland, we presented some data from the colony Moerdijk, the Netherlands where graellsii and argenteus breed in several 1000’s. Chris Gibbins asked to say something about heuglini as well, just to compare the available data. I will copy the figures from that talk below in this mail.
Figure 1: Grey tone on Heuglini, compared to argenteus and graellsii from the colony Moerdijk, the Netherlands (2006-2007).
Figure 2: Heuglini black on primaries. Heuglini data Buzun 2002; Graellsii data Moerdijk. Heuglini has a tendency to show on average more primaries with black; but the overlap with graellsii is complete.
Figure 3, 4, 5: Pattern on P9 for graellsii (Moerdijk), heuglini (Russ Zavorot) and heuglini (Ob).