Saturday, July 13, 2019

Shibden Park

As I approached the lake at 0945 I saw a Great Egret flying above the water. It did a couple of circuits below tree height, then departed over the trees to the southwest.


 The white cygnet has pale legs, and a pale bill (contrast bill of the normal cygnet at top of first picture). But it has some brown in the plumage, so does this mean it's not a Polish Swan?   Note: Thanks Andy for the reference to the BB article on Polish Swans ( britishbirds.co.uk/article/polish-mute-swans/  ); the photo with this article shows a bird with a similar amount of brown to ours, so ours looks good.

4 comments:

charlie streets said...

Fantastic find in the most unlikliest of settings!

Dave Franz said...

Well done with the Egret Peter.

David Sutcliffe said...

Later seen at Cromwell Bottom then flying off towards Elland at 16:10

Peter Smith said...

Thanks very much Charlie and Dave. Re the swan, Andy's 2016 article mentioned that Moss Taylor in Norfolk was compiling a national survey of Polish swans, and wanted records. So I sent my photos to Moss, and he has kindly replied and confirmed that ours is one. However, his survey has finished, with the results in a very detailed BB paper on Polish swans: British Birds 111:10-24 (Jan 2018). The sex chromosomes in birds are W and Z (not X and Y), and contra to mammals it is the male that has 2 the same, ZZ. A gene on the Z chromosome controls melanin production. If this gene is faulty - and the bird does not have another normal one - melanin production is impaired: the Polish variant. Therefore, a Polish swan with normal parents will be female, with a father having one faulty Z chromosome.