First Week in May - Tuesday 5 to Thursday 7 May.
Another week spent looking for seabirds, particularly Short-tailed Shearwaters, and I thought I'd missed out again until ...
very early morning on Thursday. It passed in less than one minute, about 400 yards offshore, typical and good enough for me.
These birds fascinate me since the discovery of their annual spring passage through HK waters in 2006. Why do we see them in Hong Kong in such a focused period, mostly the last week in April and the first two weeks in May, when they should be so far away in the Pacific Ocean somewhere?
The answer can come partly from a paper published in 2014 by CSIRO in Australia, "Trans-equatorial migration of Short-tailed Shearwaters revealed by geolocators". It has long been known that the 20 million birds breeding in southeast Australia migrate across the Pacific to the cold waters north of Japan for their non-breeding season, our summer. But the migration routes and timing were not known, until birds fitted with geolocators in their breeding season in early 2008 were recovered later that year.
20 birds were recovered and their travels during 2008 are given in this diagram
Firstly after breeding, they travel southeast to Antarctic waters south of New Zealand, to fatten up for their long journey. Then they set off, first north and then northwest, to their wintering grounds in the seas off Japan. This journey of 11,000 kms is covered in about 13 days or about 840 km per day, so very quickly. It is unlikely they feed during this migration.
All these movements are very consistent in timing, at least between this 20 birds from one breeding location. Eleven of the twenty arrived in Japan in just two days, on 29 and 30 April.
So how does this compare with what we saw in 2008, and what we consistently see each year for this species?
Firstly, just like the main migration, our birds are very consistent in their timing, more than 40% of HK records occur in the seven days between 10 and 16 May. In 2008 that number was 76%, 25 out of 33 records that year.
But why the delay of about two weeks between our records and the main arrival in Japan? The distance is about the same. But if they are travelling at 840 kms per day, they can travel a long way in that extra two weeks.
Obviously our birds get diverted from the main track somewhere, possibly in the Indonesian islands. Or they may even go the wrong way around Australia, or even up into the Indian Ocean before finding their way back - there are records at this time from the Straits of Malacca between mainland Malaysia and Sumatra. We just don't know the answer to this yet.
Next week should be a good week for this species, and I will be there on Po Toi from Tuesday to Thursday trying to catch the peak passage.
What else this week? Very few seabirds, a few Black-naped and Bridled Terns from local colonies and one Greater Crested.
On land, the southerly winds and lack of rain meant almost nothing arriving. We have had southerly winds non-stop from 24th April to today, and on for at least the next nine days according to the forecast. And with this, on Po Toi at least, no rainfall. So just some migrating egrets, the White-breasted Waterhen still on the South Peninsular, an Oriental Pratincole, a Dollarbird, several Yellow and eight Grey Wagtails, up to five Brown Shrikes, single Grey-streaked and Asia Brown Flycatchers and Little and Black-faced Bunting - poor fare for early May.
No sign of the Fairy Pitta I was hoping for - but the stream it uses is totally dry this year. The biggest surprise was a Hill Myna which spent five minutes in the tall trees by the school
From today (Friday 8 May) to Tuesday 12 May is the Po Toi Festival Week - Opera, Dragonboat Racing and thousands of people in the main Village area.
Here is the revised Ferry Timetable for that period
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Last edited by wgeoff at 8/05/2015 09:23 ]
