mystery shelduck at WTP, Werribee, Victoria

Hi, 
  
There is a strange looking shelduck at the Western Treatment Plant (near Werribee, Victoria) at the moment. It was initially found and reported by Gina Hopkins about 4 months ago, and seen by Maarten Hulzebosch who noticed its potential similarity to Cape Shelduck (a South African species). It then escaped notice until Bob Swindley relocated the bird last week and on Tuesday 17th, Richard Loyn and Danny Rogers were able to spend half an hour enjoying good views of it; Rohan Clarke saw it the next day. Others looked for it today with no luck.  Both Danny and Rohan obtained some low quality photos of it. None of the observers have been able to make a positive identification.  The bird does have some features of Cape Shelduck, and other features that do not fit the pictures we have seen of that species.   
  
If you go looking for it, it has been on 145W Lagoon, Pond 18 - after you have crossed the Little River Ford and turned right towards the coast, that's the 4th large pond on your left, before the cattle grid. The bird has been perching on the banks on the north-western corner in company with a large flock of Australian Shelducks, and swims into the middle of the lagoon when disturbed. First impressions are likely to be of a shelduck with a conspicuous light brown head. 
  
On closer examination the bird differs from Australian Shelduck in many ways. While similar in size, it appears to have a longer tail; the bill appears a little shorter and finer, and the head appears rounder, with a steeper forehead. The breast is bright rufous, similar in colour to the breast of male Australian Shelduck, but that's about where the similarity ends. The head pattern is very strange and distinctive: mostly light greyish brown, with a dark brown hindneck and crown; the dark brown of the crown broadens and projects down to surround the eye, and there is a diffuse, very pale brown wash across the upper face, appearing strongest behind the eye. Most of the body is warm brown - not as rusty as a Ruddy Shelduck, but certainly not the blackish colour found in Australian Shelduck. It has deep rufous tertials, and very distinctive rufous undertail coverts and vent, neatly separated from the flanks by an iridescent blackish line that runs down from the rump towards the!
  cloaca. We heard the bird call three or four times (it was the only duck on the wetland that was calling) - it was similar in pitch to female Australian Shelduck, but it was a single note call with a rising inflection "kror". 
  
ID still baffles us, but it is very difficult to reconcile the appearance or call of the bird with Australian Shelduck. The possibility remains that it is a Cape Shelduck, a South African species never before recorded outside Africa.  This is by no means confirmed; most plumage characters seem OK but the head pattern is inconsistent with the better known plumages of that species. However we do not know a great deal about immature Cape Shelduck. Another possibility is that it is a hybrid, perhaps involving Ruddy Shelduck which is kept in captivity. The head is darker than the breast, and several other features rule out Ruddy Shelduck itself (a much more likely species to occur than Cape Shelduck, either as a vagrant or an escapee).  If it is a Cape Shelduck, the brownish head would make it an immature, and we have seen no good photos of immature Cape Shelduck. The species is said to be quite common in southern Africa, and makes regular movements to moulting areas bu!
 t no long-distance migration. 
  
Whatever the duck is (and wherever it came from), it is a good-looking and interesting bird, well worth a look if you are passing that way. Please remember that you need a permit and key to get into the Western Treatment Plant, and try not to disturb the bird unnecessarily, not least as relocating the bird (among the 100,000 waterfowl that occur in the WTP) would be a a tricky proposition. If anyone obtains better descriptions, photos or recordings we would be very interested. 
  
Richard Loyn 
Danny Rogers