Wednesday, 5 June 2013

Hybrid Black Redstart x Common Redstart

One of the most interesting, if not perhaps exciting, birds of the trip was the (presumed) hybrid Black Redstart (svartrødstjert) x Common Redstart (rødstjert) at Næroset in Hedmark. This bird is frequenting a timber cutting plant by a lake surrounded by forest. There are a number of buildings here and the bird was to be found singing from roof tops and the tops of piles of timber. We saw it also feeding on the ground on the edge of the plant searching for insects amongst wood cuttings and on rough ground.

The bird was initially reported as a Black Redstart but pictures showed it to be abnormal. It had reddish underparts and lacked the jet black colours of Black Redstart. The song however was reported as being identical to Black Redstart so many people reported it as a Black Redstart. The question was raised as to whether it could be an eastern race of Black Redstart which show red underparts but these birds have much brighter underparts and also still have the jet black colours of Black Redstart. I was one of a few people who expressed a view that it was a hybrid with Redstart. This hybrid appears to be reasonably regular further south in Europe where both species are common breeders but is not a hybrid form that existed in the Norwegian reporting system indicating that it has not been reported in Norway before. This is not surprising as Black Redstart is such a rare breeder in Norway but I did see a male Black Redstart and female Common Redstart together on the roof tops of Oslo in May 2011.

There seemed to be little agreement from those who had seen the bird in the flesh that it was a hybrid and I was “challenged” on Facebook to go and see the bird live to sort out its identity. Luckily our route on Sunday took us past the site and we ducked under a barrier and made our way into the timber plant.

It seems likely that this bird was actually born on this site. In 2011 twoBlack Redstarts birds were reported as being here throughout the summer and a third bird was found dead there in May. Successful breeding was not reported but birds were present from May until July including a singing male. It is not easy to age this bird. The brown fringes to the flight feathers, lacking the white wing panel of an adult male Black Redstart and a generally subdued plumage suggest 2 cy but given that it is a hybrid I cannot be sure how the influence of either species will play out in the plumage (male Black Redstarts normally do not acquire full plumage until their 3rd cy and are much more female like but male Common Redstarts in their 2nd cy only look only slightly less bright than an adult male). The throat and bib look very black but closer pictures show there to be brown fringes to the feathers which is also a sure sign of 2 cy. No birds were recorded in 2012 but it is possible that female returned in 2012 and went unnoticed due to not singing. There are Common Redstarts in the area (we heard a male singing) so she could have paired with a Redstart and they could have produced young

Another interesting aspect was that we momentarily saw it interact with another Redstart sp. amongst a woodpile. We never saw the other bird properly but appeared to be in female plumage. Maybe it is paired to a female (Common?) Redstart?

Plumage wise it is, to my eyes, closer to Common Redstart. It differs from Common Redstart by having less orange underparts, lacking a clear white forehead (although it does have a white feather on the right hand side) and the black throat extends further down the chest. Generally though the greyness of the plumage on the mantle and nape matches Common Redstart.
Black Redstart would have grey underparts (not the pale orange of this bird) and wouldn’t have such a clear border between the black throat and the paler belly. Adult males of the eastern subspecies would have the black extending further down the belly and then a clearer border to a deeper orange belly. Given that Eastern Black Redstarts are a real rarity in Western Europe and can resemble hybrids there has been some research into how to separate them. The surest way is on wing formula as Black and Common Redstarts have different spacing between the primaries and this can be seen on good pictures. Unfortunately I was not able to take a good enough picture of the wing but I believe that the plumage alone allows an Eastern Black Redstart to be ruled out.
You can judge for yourself in the pictures. The pictures were taken in different lighting conditions and at some distance so note how the plumage colours can vary. I have therefore included a number of pictures with different backgrounds to allow all the subtleties to be seen.
Hybird Black Redstart x Common Redstart. This picture shows the white feather in the crown, the pale orange underparts, grey mantle and a black throat and bib that stretches too far down the chest for a Common Redstart
Here the bird gives a very Common Redstart impression although note that the forehead is burnt out so looks paler than it actually is
Again quite Common Redstart like with the underparts being far too pale for Black Redstart

The extensive black throat and bib are too extensive for Common Redstart

Here it is possible to see paler edges to some of the throat feathers suggesting 2 cy

The white feather in the crown is again visible here

The pale grey as opposed to dark grey/black upperparts give more of a Common than Black Redstart feel

In this picture though it does look very black on the throat and bib but the pale belly is just not right for Black Redstart

The song of the bird can be heard in this video. It does sound very like Black Redstart especially because it contains the scratchy/crackling static element that is not in the song of common Redstart but isn’t the song of Black Redstart also quite similar to Common Redstart except for the scratchy bit? I don’t  know how the song of a hybrid usually is. Will it be influenced (learnt from?) by its father or is it all genetic? In the video you can hear the scratchy bit of the song well when the bird is closest. In the sequence when it is further away you don’t actually hear the scratchy sequence although can see that the bird is singing (this is the same as in the field when the scratchy bit is only audible close up).

Comments as to the ID of this bird would be welcome.

No comments:

Post a comment