Statistically, extralimital wildfowl will always have the potential to have ‘escaped from captivity’. Markers of captivity – rings and flight feather damage only point to the most obvious of escapees.
Logic would suggest that extralimital species like the Mandarin, which migrates southwards in the winter , may over shoot in the Autumn and end up in HK.
As always, first winter birds are less good at navigating and a first winter Autumn Mandarin is going to be your best candidate for vagrancy – I am unaware of any identification criteria that point towards a 1st winter bird and I think they basically look like a female.
Spring birds will be birds moving back North but would have had to have wintered further South, which statistically is less likely. Naturally, captive birds which have been transported further South and then escaped, will be among the most likely group of Mandarins to turn up in Spring.
As always, there are things that some birds do that seem totally unpredictable; this is probably more to do with our understanding of the weather systems and circumstances that go with the individual bird rather than them being totally random events.
There is hope with isotopes studies on birds feathers to determine the origin of where the bird was feeding when it produced its latest batch of feathers.
Much of this is 'work in progress' , but it won’t be too long before ( and may actually be possible already) stable-hydrogen isotope analysis in feathers can be used to work out whether this Mandarin spent its winter feeding in Thailand or China! All you need is a feather for analysis and a large wallet.
Many of you will be aware of the usage of these scientific techniques in European Baikal Teal records to show a Siberian origin of individual bird/s.
http://www.surfbirds.com/forum/showthread.php?t=6201
Here are some articles you may find of interest.
http://blx1.bto.org/pdf/ringmigration/24_3/coiffait.pdf
http://www.americanbirding.org/p ... l36no2p142to145.pdf
If you have problems downloading them, drop me an e mail and I can send you the pdf.
eric
