The eastern lesser whitethroats in Skagen

NYT FRA FUGLESTATIONERNE Skagen fuglestation har netop modtaget DNA svar på de to gærdesangere fra ultimo oktober 2019. De to fugle blev beskrevet i en særskilt engelsksproget artikel (se link til artiklen nederst). Det viste sig at begge fugle tilhørte underarten blythi. I artiklen bliver mulighederne for feltbestemmelse overvejet og diskuteret, og man kan se hvor Skagens fugle er placeret i et cladogram over de forskellige underarter af gærdesanger.

DNA-Results of two Eastern Lesser Whitethroats

In October 2019 two Lesser Whitethroats with characters suggesting one of the eastern subspecies ssp. blythi or ssp. halimodendri were caught and ringed at Grenen, Skagen by the team of Skagen Bird Observatory. Feather samples were sent to Martin Collinson and his team at the University of Aberdeen, Scotland for mitochondrial DNA-analysis.

De to sibiriske gærdesangere ssp. blythi fra Skagen ultimo oktober 2019. Foto: Skagen Fuglestation

The Observatory has now received the interesting answer of the tests. The results showed for both individuals to be ssp. blythi (Siberian Lesser Whitethroat). Below a cladogram of the different Lesser Whitethroat subspecies, with the two individuals from Skagen.

Cladogram showing the two individuals from Skagen, represented as orange squares, matching the taxa of Siberian Lesser Whitethroat (ssp. Blythi). Collinson, J. M. University of Aberdeen, Scotland.

The morphological difference between ssp. blythi and ssp. halimodendri are very slight and currently it is probably not safe to separate these two taxa from each other only by visual appearance in Western Europe. In hand and field the second individual (caught on the 22ndOctober) had measurements and characters pointing towards ssp. blythi. Furthermore, it also had a “check” call and not a rattling call. But the first individual (caught on the 20th October) showed some characters and measurements in favor of ssp. halimodendri – but tail pattern was pointing more towards ssp. Blythi, which witness of how difficult it is to separate these two taxa. In appearance, the second bird resembles another Danish record of ssp. blythi from Anholt in 2012 (confirmed on DNA), where also measurements and coloration pointed towards ssp. halimodendri but tail pattern was pointing towards ssp. blythi.

Even though that the separation of the Lesser Whitethroat subspecies is highly complex, every good documented record in both field and hand will get us more knowledge about the characters and calls. Currently, we probably still need to rely on DNA-analysis for separating ssp. blythi from ssp. halimodendri but this could maybe change with more knowledge. Another relevant question is if we can safely separate birds of the eastern sub-species from our own nominate ssp. curruca in field. For example, late autumn birds documented well with sandy color, short wing, much brown in head, much white in tail or rattling call. In my opinion, I believe we are close to be at that point now where this should be safe in some cases. This is also supported by many recent cases in Western Europe where eastern origin was suspected with the birds in hand/field and later confirmed by subsequent DNA-analysis as either ssp. blythi or halimodendri. It would be interesting to see if there any cases of birds suspected to have eastern origin in hand but turned out to be ssp. curruca on DNA in Western Europe.

Read more about the two birds from Skagen and the current status in Denmark of ‘Eastern’ Lesser Whitethroats in this article from autumn 2019: “Eastern Lesser Whitethroats in Skagen”

Thanks to Martin Collinson and his team for taking care of the DNA-analysis.