sgbeachbum: whimbrels

April is when the visiting shorebirds fly up North back to their summer breeding grounds. They will not be back until September-October as part of their annual cycle. In the videoclip, the birds appear to be rather plump as they fly past. Looks like they had a successful Winter stayover at SBWR.

All that feeding on the Mandai mudflats at low tides has paid off to restore the energy stores on these long range birds. They have to make the flight back up North. This is no easy task. This last weekend may be their last or rather our last opportunity to see the flock of whimbrels (numbering about 165 at the highest count this year) fly to, fro and about the Sungei Buloh Wetland Reserve along with about 60 greenshanks and up to about 250 redshanks for companionship. The counts vary every few days from September through April as the birds may alternate between roost sites.

Their reliance on the coastal mudflats is absolutely crucial and the birds' flight out from SBWR to the Mandai mudflats everyday in expectation of the best low tide window to feed is indicative of the importance of the mudflats for the birds. Without the rich feeding grounds presented by the mudflats and the safe open roosting sites nearby at SBWR, these birds would have disappeared from our skies in search of the right combination of feeding and roosting grounds elsewhere. Indeed, the numbers of shorebirds at SBWR ten years ago were in the thousands. In recent years, the number has reduced to just a few hundred and with a reduction in the number of species also. The reduction could be explained by the shorebirds preferring alternative roosting sites instead of SBWR.

Given that most of the shorebirds prefer open roosting grounds, it is possible that recent (within the last 4 years) mangrove land development across the Johor Straits has made open grounds temporarily available and the birds have flocked there instead. When the builders move in on that cleared land, the birds may choose to roost back at SBWR's open controlled water level ponds. It takes about 4 minutes for the birds to fly between SBWR and the Mandai mudflats and this short flight enables the birds to burn only a small amount of calories allowing them to stock up on their reserves without expending too much energy each day flying to and fro. Each day, they may get about 5 to 6 hours of feeding at the mudflats or more depending on how low or high the tides for the day were. The moon's effects on the tides nevertheless plays an intrinsic part as to how much the birds can feed each day. They even feed throughout the dark of night at Mandai if suitable low tides present themselves overnight.

Given that the SBWR birds often roost within the controlled ponds and do not have sight of the receding tides, the birds must have an innate sense for knowing when to fly out for the low tides. Generally, they fly out about 2 to 3 hours before the lowest tide and they fly back in about 3 hours after the lowest tide. The timing depends on how fast or slow the tides move. Sometimes, the birds are a little delayed in their departure out from the controlled water level ponds (where the water level does not change with the tides). This could be due to the 'leader' birds themselves losing track of tides and delaying their flights out.

Flying back is necessarily dictated by the rising coastal waters and the average length of the whimbrel's legs. Usually, the smaller plovers (eg. mongolian, pacific golden) take off first with the rising tide followed by the redshanks, then greenshanks. The whimbrels leave last. The whimbrels and greenshanks were not seen on 22 April 2017. It is possible they finally flew North sometime during the week. There were still about 30 redshanks and handful of pacific golden plovers seen at SBWR on 22 April 2017. Last chance to see them before they too fly North this year.

Flight of the Whimbrels @ Sungei Buloh Wetland Reserve - 16Apr2017 from SgBeachBum on Vimeo.

Interesting links :
https://www.facebook.com/AWSG.sat.tag/?hc_ref=PAGES_TIMELINE&fref=nf

https://www.youtube.com/watch?v=W95SJ6BLdG0 - An Interview with a Bar-tailed Godwit.
https://www.youtube.com/watch?v=MRPZYjsMUZ0 - Oh My Godwit, The longest bird migration in the world.
https://www.youtube.com/watch?v=Q-mMMpl_T80 - TedEd - Bird Migration, A Perilous Journey
https://www.youtube.com/watch?v=Ahm9x8QTQJk - the physics of bird migration
https://www.youtube.com/watch?v=4JUYyMHOHb8 - how do birds know where to go when they migrate?
https://www.youtube.com/watch?v=CwIT9pv4kh
https://www.youtube.com/watch?v=WhwBDjfWr_M
https://www.youtube.com/watch?v=8FcCJIpsH0U

http://www.worldmigratorybirdday.org/news/2017/stopping-habitat-loss-china-proposes-yellow-sea-be-added-world-heritage-tentative-list-0

http://www.birdlife.org/worldwide/news/chasing-ghosts-how-technology-helping-track-bird-mysteriously-disappeared

A flock of about 35 whimbrels flying off from Eagle Point (Singapore) across the Straits of Johor (Malaysia) towards Sungei Danga/Sekudai in Johor. The incoming tide chased the birds off for the evening. Eagle Point (part of the Sungei Buloh Wetland Reserve) is at the western edge of the Mandai mudflats which is a rich coastal mudflat area which the shorebirds feed at during the lower tides. As the incoming tide rises, the shorebirds fly off to roost at either the Sungei Buloh Wetland Reserve nearby or across the Straits of Johor towards the Sungei Danga/Sekudai mangroves. Time : 6.36pm Tide : 0.9m @ 3.30pm, 2.9m @ 9.30pm The clip was shot at 96fps and played back at 24fps. Certain sections were sped up (especially where the focus starts to suffer and the birds are far away enough to start merging into the background.)

Whimbrel Flock flying towards Sungei Sekudai - 12Nov2016 from SgBeachBum on Vimeo.

The red lines show some of the routes taken by various groups of shorebirds to and from the Mandai mudflats from roosting sites at SBWR and the Danga-Sekudai rivers. There may be other roosting areas (eg. Sungai Melayu) closeby too. (Music : Symphony No. 4 in B-Flat Major : Op 60 IV. : Allegro ma non troppo)