Dark morph Marsh Harriers

Since the start of the count we have seen a lot of Marsh Harriers. At least 16 of them were adult males of the rare dark morph. In former years only a handful of dark birds passed the stations. Little is known about this morph, e.g. where it originates from and what percentage of the population shows this plumage. Forsman (1999) noted that this morph comes from more eastern populations and migrates through the Middle East.
Adult males can be rather easily distinguished from the Western European plumages of the species. They show a dark brownish colour, a distinct white distal part of the remiges and a dark greyish area in the upper secondaries. Second calendar year males can be sometimes tricky to identify, but they show a more light brownish colour, yellow crown and less contrast in the secondaries. Females and juveniles of this morph are expected to be hard to distinguish.
Compared to the numbers that has been reported from Israël (on average 2-3 every autumn), our number of this autumn is already interestingly high. Do we have a lot of eastern birds this year, has the morph been overlooked previously? There is still a lot to figure out.
written by Albert de Jong – 10/9/2012