ajohn

Maybe I've missed something, but I don't see any evidence that the Ferruginous Duck is moulting. In fact, I think the the photos of spread wings show that the feathers are fully grown. The same is true of the Greylag Goose, which also shows fully grown wings with no moult or damage.

Having seen the goose on Saturday, the thing that really struck me was how cautious this bird was. Note that the good quality pictures make this bird seem much closer than was actually the case. It stayed about as far from land as possible, and was scared of everything - even flushed away by a Black Kite flying over. Even when near other birds (egrets) for security, it was constantly on the lookout because it was so nervous. I find it hard to imagine that this bird had spent any time in an enclosure, and it definitely looked wild. I have absolutely no doubt that it would have passed the 'bread test' Jonathan mentions (it would have flown away when you were several hundred metres away, let alone being close enough to throw any bread).

I admit that I had exactly the same thought as Jonathan when these two species turned up in 2012 (coinciding as well with the Oriental Stork...). They ought to be much further north than HK at this time of year. But now that it has happened again, with the same two species, I am siding with them being wild birds. If these are escapes from captivity, then why are the same two species involved both times and why have none of the four birds shown any evidence of captivity (e.g. no damage to plumage or bare parts, no leg rings). Maybe there is something about the weather conditions at this time of year which may force the birds to move - perhaps some of the breeding or moulting sites are drying out and birds are forced to travel to look for food. This has been suggested for potential vagrancy of Marbled Duck and White-headed Duck during July/August in Europe (wandering north as wetlands in Spain/Portugal dry out).

ajohn

Wilson, I think the 'tilting' you refer to is actually fairly normal for a bathing duck. I think they typically lower one side into the water so that the wing can flip water onto the back.

Jonathan, regarding your revised theory, a couple of questions for you to consider.
- If these are from a released of 57,000 ducks in 2013, why would they turn up here in the middle of 2014? They could have turned up at any time over the past few months, but there is no suggestion that they have done so.
- Having turned up at Mai Po, why did the goose leave so quickly - if it has been wandering Guangdong for some time looking for somewhere safe and undisturbed, Mai Po should be a good place to stop. The previous summer Greylag and Ferruginous also stayed for only 1-2 days.
- Why do we not see similar summer records with the other species you mention (Red-crested Pochard, Baikal Teal, Scaup)? Wouldn't obvious escapes also turn up at other times of year? And why do we not see hybrids of the type you mention (Pintail x Falcated)?
- Finally, why do these birds not show any sign of damage to plumage or bare parts? It was very obvious on the winter Greylag a couple of years ago (http://www.hkwildlife.net/viewth ... &extra=page%3D1 and http://www.hkbws.org.hk/BBS/view ... p;highlight=greyleg) and you mention that the geese you have previously seen in the market were in very bad condition. Your theory about recent wing moult may have some validity, but that doesn't explain the lack of damage elsewhere on the bird(s).

I agree that on the basis of range, wild Greylag Goose wouldn't be expected to turn up in HK in summer. But with two birds, neither showing no clear evidence of a captive history, maybe there is something about their migration we don't yet understand.