Saturday 19 September 2009

Lesser Black-backed Gull (Larus fuscus intermedius), 1cy, 19.9.2009, Aarhus North Harbor

This bird has initially been identified as a possible fuscus based on the striking plumage. It is a pale, heavy contrasting plumage where the bird has pale face and hind neck, whitish feather edges on a very dark brown blackish mantle and scapulars, and pale unmarked under tail coverts, belly and central breast in combination with whitish underwings. Additionally it has an almost complete juvenile plumage even by late September with only two scapulars renewed which is atypical for an intermedius.

But this juvenile bird has now been seen call for food from a pair of adult intermedius throughout September and it therefore most likely belongs to the local population breeding on buildings in Aarhus. The extreme fresh juvenile plumage by late September would then be explained by the bird being a late fledged individual compared with the standard intermedius.

The bird looks very unlike a typical juvenile intermedius, but it is seen associating with adult intermedius where it beggs for food and so should therefore be an intermedius. So why does it not look like one? Two possibilities exist. The first is that it is a pure intermedius, but a rare variant that is inseparable from Baltic Gull by plumage at this age. Secondly there is the possibility of hybridization as an explanation for the odd appearance of this individual. For the moment, it seems prudent to leave such individuals aside and develop identification criteria based on the more typical birds.










3 comments:

JanJ said...
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JanJ said...

Hi Kent!

Lade märke till till stjärtteckningen på denna fuscus (förm. fuscus fuscus), marinus lik.

Flotta bilder!

Hilsen
Jan Jörgensen

Kent Olsen said...

Hej Jan,

Mange tak for din kommentar, den er værdsat og jeg håber du vil kommenterer om du finder nogle af mine bestemmelser tvivlsomme eller ser gode dragtdetaljer som du ønsker at fremhæve

Jeg tog friheden til at slette din første kommentar da den indholdsmæssigt var identiske med den anden, håber ikke det støder

Havde netop fuglen mistænkt for at være en fuscus fuscus grundet den meget kontrastrige dragt med generelt meget mørke fjercentre og hvide fjerkanter, og grundet det udpræget lyse hoved og den meget lys undersiden som sådan, herunder med umarkeret renhvid undergump, bug og centralt bryst og lyse undervinger. Desuden er fuglen i komplet juvenil dragt med vist kun to skulderfjer udskiftet

Studsede meget over halebåndet, der er underligt i forhold til det jeg kender for arten, og det er derfor forsøgt fremhævet med billederne, du har ret, det minder meget om Svartbag (marinus)

Fuglen er formentlig en han grundet kraftigt næb og kropsstørrelse, relativt stor fugl om end slank og langstrakt

Igen tak, Kent