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Cormorants between Deep Bay and Starling Inlet 到沙頭角海覓食的鸕鶿

Cormorants between Deep Bay and Starling Inlet 到沙頭角海覓食的鸕鶿

Just last Sunday (about 10:00 AM 24 Jan 2010), I saw at least two flocks of Great Cormorants (total about 100 birds) left Starling Inlet and flew towards the Fanling drection.

There were about 270 cormorants in Starling Inlet yesterday. Currently there is no wintering roosting site of Cormorants at Starling Inlet but there was such roosting site on A Chau ten yrs ago.

As the presence of roosting sites of Cormorants between Deep Bay and Starling Inlet are highly unlikely, so the Cormorants were supposed to fly towards Deep Bay.

Not sure whether there are such sightings. It is interest to know that Cormorants at Deep Bay could reach Starling Inlet for feeding. The distance apart is about 20 km. Probably takes about half hour each way.

Mike and I saw such Cormorant flock at Lin Ma Hang in 2004 but not 100% sure the destination.

The tide was high at that time when they left Starling Inlet. It is reasonable to guess that they left Deep Bay at dawn and then return to Deep Bay when the tide at Starling Inlet was tide. So, they may have had about 4 hrs to feed at Starling Inlet.

Questions about this sighting are

1. why these Cormorants did not stay at Deep Bay to feed? reduce competition with other wintering Cormorants? What is the trigger level? i.e. when wintering population reaches to certain number of birds, some will travel to Starling Inlet

2. why they don't stay at Starling Inlet? Not enough food to allow establishment of a wintering pop at Starling Inlet?

3. How often did they travel to Starling Inlet? Every day? or just early morning low tide in Starling Inlet?

4. Did the number of cormorants travel to Starling Inlet vary every day?  

5. What's the energetics of such "long haul" flight? Did they really get more food in Starling Inlet than Deep Bay? Or just a gamble.

昨天 (2010年1月24日上午十時左右水漲時),我在沙頭角海看到二群鸕鶿(共100隻)沿沙頭角路離開沙頭角海。由於沙頭角海至后海灣並沒有鸕鶿的冬天休息點。所以有理由相信這些鸕鶿是回到后海灣米埔一帶的冬天休息點。換句話說在后海灣一帶的鸕鶿,是會到20公里外的沙頭角海覓食。

估計這些鸕鶿於黎明時離開后海灣,所以應有約3-4小時的覓食時間。

有關的問題是

(1)        為什麼這些鸕鶿要離開后海灣到沙頭角海覓食?因為減少競爭?若是的話,后海灣鸕鶿要到哪個數量,才會促使牠們飛到沙頭角海覓食?

(2)        為什麼牠們不逗留在沙頭角海休息?不夠食物去維持一個固定渡冬群落?

(3)        到沙頭角海覓食是否每天定期?或只在沙頭角海早上潮退時?

(4)        到沙頭角海覓食的鸕鶿數量是否穩定?

(5)        飛到「老遠」的沙頭角海覓食是否合乎經濟原則 (從覓食攝取到的能量多過耗用在飛行上?或者這只是場賭博。

[ Last edited by wcaptain at 25/01/2010 15:15 ]

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萬宜水庫也有一群鸕鶿(13隻左右)
在金山的水塘也曾發現過一隻
另在黃昏時間在尖沙咀也可以看到鸕鶿由東至西飛過維港

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Quote:
Original posted by lalan at 25/01/2010 17:01
另在黃昏時間在尖沙咀也可以看到鸕鶿由東至西飛過維港
是! 我也在黃昏見過兩次有一群鸕鶿沿海岸線由紅磡飛越維港上空到尖沙咀海運碼頭,然後轉向北方向西九龍飛去!每次大約十多隻!

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