thinfor

Hi all,

As the subject shown, I would like to get some ideas from experienced birders about the impact of the climate to migrating birds.  Not sure whether I have put my thread into a correct place.  Please be moved to a more appropriate one if necessary.

Recently, I was quite shocked by the bird species being seen;  Oriental Stork, Greylag Goose and Ferruginous Duck.  They are quite rare and even more surprising that they have been seen in summer.

I remembered that around early July, there was an anticyclone developed in Mainland China, bringing strong wind from North or North East.  This was not so common indeed because from my understanding strong anticyclones in Mainland China are usually developed in winter.  Supposing that those 3 species appear commonly in Mainland during summer, would that be the case that they were drifted by the anticyclone when they migrated (or whatever purpose they flew)?

This idea is stimulated by Geoff as he has been doing so much great work on observing and studying the impact of the weather in southern Hong Kong that may influence our HK bird counts.  Maybe the uncommon anticyclones or strong gust from Mainland in summer has contributed recent birds found in MPNR?

Just a wild guess and welcome for comments from the experienced.

wcaptain

When considering the occurrence of rarities in HK, I think we should not focus on one assumption first.

We should explore reasonable theories and pick up the likely one to further investigate.

If you have an assumption first, it is easy to have an answer before any examination of facts and observations.

My initial thought is wandering of young or immature birds. Pls note that some of the birds you mentioned are large waterbirds. their range of movement is really great and out of expectation.

thinfor

Thanks for your comments and guidance.

Actually I don't think I assume anything.  If I did, I thought I assumed that the weather system might somehow divert or drift the bird migration route, which was highly likely, especially during high migration season.  Instead of putting rare bird records as the consequence and the strong anticyclone as the only reason behind, what I think is the other way round.  Any consequences may result if there is any strong wind like anticyclone in Mainland during summer time?

That's why I said it's an idea.  If we collect enough weather information and birding records in the past history, we might discover some correlation between the weather and the birding reports that we had (here, of course the weather just narrows down to the strong weather system in summer like the anti-cyclone I've mentioned).

A pity that we may lack data and time to do further investigation.  Also, no birding reports do not mean the birds have not come.  They were just not being seen.

wgeoff

Hi Manson, an interesting thread.

These days when looking at the origins for rare birds, we usually go first to the Backward Trajectory Maps produced by HKO (on their website, under the heading 'Weather Monitoring Imagery'). You can quickly scan through the daily images for July under 'Past Backward Trajectory Map'.

There is nothing here for to suggest a wind assisted northern origin for these recent arrivals, all the daily trajectories for July are coming from the south, as you would expect at this time of year. I think as Captain says, wandering immature birds is a more likely explanation, that is assuming they are all wild birds which they may not be.

ajohn

I think that if the occurrence of these birds was weather-related we could expect to see a change also in commoner bird species. There have been no arrivals of e.g. Teal or Garganey associated with these birds. This suggests to me that it is not due to the weather.

Both the Oriental Stork and the Greylag Goose appear to be adults. I'm not sure about the duck. This would seem to go against Captain's theory (although perhaps not entirely - they could be young adults).

I suspect a different origin for all three birds, with their occurrence at a similar time being partly coincidental and partly the result of increased observers at Mai Po compared to previous Julys. The duck was only seen by an observer who had come to Mai Po to see the stork.

Vagrancy by storks in late summer is an established phenomenon elsewhere I think. (European) White Storks that have not bred will wander widely, away from the usual breeding range. There seems to be no real reason that Oriental Stork should not do the same. With a breeding population now in the Yangtze Valley, I suspect that this is a bird from that population that has not bred (perhaps too young or could not find a mate) and has wandered around south China.

Geese should now be moulting a long way to the north of Hong Kong. Theb Greylag Goose seems to be an unlikely vagrant at this time of year, especially an adult which should know its migration route. Of course, there was a known escape in Deep Bay last winter - I suspect that this is the same bird, which has subsequently moulted feathers back and has healed on the bill.

That just leaves the duck, which I am still puzzling about. There is a previous mid-summer record of Baer's Pochard. The first sighting of Red-crested Pochard was also mid-summer - this is currently treated as an escape, but with a breeding range similar to Ferruginous, could there be a possibility of both bineg wild?

brendank

I think the rectrices were damaged on the Greylag. That points to captive origin. There was a Red-crested Pochard found a few summers ago at Mai Po which was badly damaged. So even though I would like to believe otherwise, I would bet the Ferruginous Duck was not wild origin. This species I believe is also relatively commonly kept in waterfowl collections.

thinfor

Thanks Geoff for the links provided, so that I could examine the exact weather before I did the proposition.

And many thanks to Captain, John and Brendan also.  I've been known that for having this kind of idea, we should firstly get the birding records that are widely spread to many common species and immature rarities have to be fully considered.  Learnt much from you all!

Knowing how birds migrate and come from and to Hong Kong are still one of my most interested topics in birdwatching.