Thursday, 8 December 2011

Herring Gull (Larus argentatus) with extreme bare part colours

On November 28th, 2011 at least 15 different Herring Gulls of different age classes were seen with abnormal bare part colours among some 700-1000 large gulls checked on Aarhus Harbour. Have they all been eating the same food with high concentration of Carotenoids?















4 comments:

ISCZ-blue said...
This comment has been removed by the author.
ISCZ-blue said...

Dear Kent,

there are several of this kind actually in Eckernförde (baltic coast near Kiel, Germany, 54.28N-09.51E) too.

You can see pictures of them in the birdnet-forum:
http://f3.webmart.de/f.cfm?id=1231426&r=threadview&t=3895089&m=16268787#16268787
http://f3.webmart.de/f.cfm?id=1231426&r=threadview&t=3895089&m=16268929#16268929

Right below my second posting you can find an IMHO plausible guess by "sternabert", that the origin of these gulls could be from areas with fishfarms. Salmons fed with food including beta-carotinoids may have caused this phenomenon.

Kind regards
Thomas Brandt

Martijn Bot said...

Hi,

two days ago, a 3CY Herring Gull kind of like "yours" came to sleep at a gull roost in the city of Groningen, The Netherlands. Never seen something like that before, maybe it is actually one of the Aarhus-birds.
Check: http://forum.waarneming.nl/smf/index.php?topic=172773.0 for a picture.

Kent Olsen said...

Thank for your comments and links to similar extreme coloured argentatus which by now have been reported from all around Denmark, at least southern and eastern Sweden, northern Poland and Baltic Germany. However, individuals are now also reported along their south-western migration route into Western Europe including the Netherlands.

It seems as if these gulls are found most abundant along the coastline of the Baltic Sea and the areas where it drains into such as Kattegat by the way of Øresund, the Great Belt and the Little Belt. Thus the source of origin should most likely be within the eastern part of this area.