Thursday, April 14, 2011

Harrier identification revisited!

In the light of Teruaki Morioka's comments, I think it is worth revisiting one particular bird seen on 24 March at Ulu Dedap.

At the time I identified this bird as a subadult male Eastern Marsh Harrier, mainly on the basis of the underwing pattern, particularly the practically unbarred remiges. However, it's now clear that I got this wrong!

Teruaki Morioka's comment: This bird is enigmatic. Its pale lesser wingcoverts suggest adult female Pied Harrier. Its underwing-coverts fit with adult female PH. Its whitish face doesn’t fit with adult male EMH, but with adult female PH. On the other hand, the blackish wing tips fit male EMH. This bird could be an older female PH. I suppose that the reduction of the female hormone could cause the bird to develop male-like features, diminishing the barrings on remiges and rectrices, and making the wing tips blackish. I believe that no adult male EMHs have anchor patterned upperwing coverts and whitish face like this bird.

This photo shows the 'anchor pattern' Mr Morioka talks about - the pattern is formed by the rather dark median coverts and the last row of lesser coverts, and upper body.

Here's the same female Pied alongside a 3rd winter male Eastern Marsh:

The first thing I notice is that the structural differences I have pointed out between Pied and Eastern Marsh are much less evident when comparing female Pied with male Eastern Marsh. The female Pied here appears large-billed and to have a prominent head. The differences in breadth of wing base and trailing edge shape are subtle, even when we have the advantage of comparing still images side by side!

Secondly, the underwing pattern of this female Pied is rather similar to that of the Eastern Marsh, and it would require close views to see the differences.

All of which makes the issue of identification rather more tricky than I had appreciated!

Note Mr Morioka's comment about the upperwing coverts and face colour.

More pics of these birds here


Unknown said...

Super complicated...hehehe..i'm learning..thanks a lot for effort putting this on your blog. Means a lot to a beginner like me.

PP said...

could understand the trickiness of this. i had a harrier shot from ulu dedap with 2 birders voting for pied harrier female and 2 voted for EMH. I am quite clueless despite all conversations.

digdeep said...

Hi Poh Peng

If you send the shot to me I'll add my vote!