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Nu staat in het engelse onderzoek dat 98% van alle Glanskoppen dit vlekje hebben. Maar het Engelse onderzoek noemt geen percentages Matkoppen die het óók hadden
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"Of the 27 live Willow Tits, pale marks were found on the upper mandible of just two birds (7.4%), with one showing pale marks on one side of the bill only and this being attributed to abrasion. The remainder all had dark, unmarked upper mandibles (Fig 1b). Live Willow Tits did show a very narrow pale cutting edge to the lower mandible that was visible when the bill was open, and similar to Marsh Tit, but this was not possible to check on skins due to the bills being rigidly closed; accordingly, only pale marks on the upper mandible were considered in analyses. Abrasion was also found on the upper mandible of one Willow Tit skin (race P. m. montana), again on one side only, although a further three (P. m. kleinschmidti) displayed obvious pale marks similar to Marsh Tit, and a further two (also P. m. kleinschmidti) showed diffuse marks, resulting in these six skins being scored as ‘1’. The other 106 Willow Tit skins (94.6% of skins examined) showed no pale marks and were scored as ‘0’."
Broughton, Hinsley & Bellamy
Separation of Marsh Tit Poecile palustris from Willow Tit Poecile montana using a bill criterion
Ringing & Migration (2008) 24, 101–103
"97% of Marsh Tits showed a pale mark on the upper mandible, on the bill sides below the nostril, which was lacking on 96% of Willow Tits (fig. 3). This characteristic mark appears to be the single most reliable and objec-tive physical feature for separating Marsh Tits and Willow Tits, although it may be very diffi-cult to see in the field. It is often readily apparent in photographs, however, although note that reflected light may obscure or mimic the feature."
Richard K. Broughton
Separation of Willow Tit and Marsh Tit in Britain: a review
British Birds 102 • November 2009 • 604–616