Main article | Peak High Tide Counts
part 1, part 2 |
Comparison of selected
species | Day Peak
Counts
Summary
Shorebirds from the Scolopacidae and Charadriidae were counted regularly in Sungei Buloh Wetland Reserve
between January 2000 and December 2006. A total of 23 species was recorded during
the census sessions. Total shorebird numbers peaked in October, November or
December for all years. The most abundant bird was the Pacific Golden
Plover Pluvialis fulva
with counts consistently exceeding 1,000 for all years since 2001 with a
maximum of 2,000.
The counts have revealed information on the composition of shorebird
species, their numbers and their presence in different months over the past
seven years. More specifically, the relative importance of Sungei Buloh as a shorebird
site in Singapore is reinforced. Data collected will help to improve the
conservation work and management practices at Sungei
Buloh for the next few years.
Introduction
This article is based on an earlier paper submitted by the same authors and
published in The Stilt No.48 Oct 2005. It is an update of the shorebird
count data obtained from monthly wader census conducted at SBWR with a
brief analysis. It is also the intention of this update to prime people to
take a greater interest and appreciation in the shorebirds of Singapore.
Results
A total of 23 species was recorded during the census sessions. Seven of the
23 species dominated with counts of at least 100 birds at any one session
during the study period. Count data for these seven species for the period
January 2000 to December 2006 are listed in Table 1. Note that the totals
as given in the tables refer to the highest count for a given month and are
not average counts.
For all years, maximum shorebird counts were in either November or December
with the exception of 2006 when it peaked in October. Peak counts of
shorebirds did not exceed 3,200 birds in any year. Only the Pacific Golden
Plover had counts exceeding 1,000 birds. This occurred fairly regularly
during both the periods for southward and northward migration. The only
other shorebird with numbers exceeding a thousand was the Mongolian Plover Charadrius mongolus (1,003 on
January 2000). Common Redshank Tringa totanus and Whimbrel Numenius phaeopus were the
only two species noted in the boreal summer for 2001 to 2006 where they
were present in very low numbers (below 20 birds) except in June 2003 when
no shorebirds were observed.
To generalise, the species with the highest numbers recorded during the
southward migration (Sep/Oct/Nov) relative to their numbers throughout the
year were Common Redshank, Mongolian Plover and Curlew Sandpiper. Species
with the highest numbers recorded during the northward migration (Mar/Apr)
were Pacific Golden Plover and Whimbrel. Species
with the highest numbers in the northern mid winter (Dec/Jan) were Common
Greenshank and Marsh Sandpiper.
Species Account
A comparison was made of the seven most common shorebird species at the
reserve with the maximum counts recorded by the Asian Waterfowl Census
(AWC) for Singapore between 1991 and 2001 (Perennou
& Mundkur 1991, 1992; Mundkur
& Taylor 1993; Lopez & Mundkur 1997; Li
& Mundkur 2004). Direct comparison is
possible for counts taken in January since the AWC counts are consistently
conducted in that month at low tide. The percentage of each species of
shorebird that can be found in the reserve against the Singapore population
is at best a rough estimate but still an indicator of the relative
importance of the reserve with respect to other sites in Singapore. The
relevant data are given in Table 2.
Common Greenshank
Tringa nebularia
Trend: Increased numbers during both
southward and northward migration The maximum count at the wetland was 364
recorded in Nov 2005. It seems likely that during high tide about half the
population of Greenshanks in Singapore use the wetland as a roost.
Common Redshank
Tringa totanus
Trend: Increased numbers during both southward and northward migration
The maximum count was 683 recorded in Sep 2000. The peaks in September
followed by a 60% to 70% drop the following month in 2000, 2001 and 2002
provide some indication of turnover rates for Redshanks on passage.
Curlew Sandpiper
Calidris ferruginea
Trend: Erratic numbers during the
southward migration. Avoidance of the wetland during the northward
migration since the spring of 2001 The maximum count was 519 in Oct 2006.
The 1991-2001 counts for Singapore range from 5 to 781. First migrants were
recorded in August. Since 2001, negligible (less than 10) numbers of birds
were present between January and July. The data and observation could be
explained by the possibility that since 2001, Curlew Sandpipers take a
northward migration route that bypass or use other wetlands in Singapore or
the region. Such an alternative route could possibly be along the eastern
coast of Sumatra before crossing over to Malaysia and/or Thailand. Large
numbers of Curlew Sandpiper occur along the east coast of Sumatra at this
time (A. Crossland pers. comm.). Wader counts at
suitable sites in Indonesia and the Malay Peninsula would help to clarify
the actual route taken. The peak counts in October for most years indicate
a strong southward passage in that month before falling sharply in January
for the northward migration.
Marsh Sandpiper
Tringa stagnatilis
Trend: Stable numbers during both
southward and northward migration. The maximum count was 486 observed in
Dec 2001. Counts for Singapore range from 526 and 1294. Birds arrive at the
wetland in appreciable numbers only from October. The data collected are
consistent with the observations in the Malay Peninsula where Marsh
Sandpipers arrive late and depart relatively early with a further peak in
the boreal spring (Wells 1999). This surge was noted in early April 2001
but not in 2000. It may however have happened between count dates and was
therefore unrecorded.
Mongolian Plover
Charadrius mongolus
Trend: Steady recovery in numbers
during the southward migration after a dramatic and steep decrease observed
in 2002 and 2003; Avoidance of the wetland during the northward migration
since the spring of 2003. The maximum count of 1,003 was recorded on 26
January 2000. Another count of 878 was recorded on 10 February 2000. AWC
counts for Singapore have recorded historic peaks of up to 1,000 birds.
Observations in the Malay Peninsula have generally noted decreases in
Mongolian Plover numbers from December to March (Wells 1999). These
observations are consistent with the pattern of counts recorded for all
years when counts are generally highest in December and decrease as the
northward migration progresses. This may indicate a boreal spring exodus
without significant augmentation by passage migrants. High tide counts
taken from a boat in the West Johore Straits on 3
Jan 03 revealed up to 600 Mongolian Plovers resting on floating pontoons.
The following year, on 6 Feb 04, 200 Mongolian Plovers were counted at the
same pontoons during high tide. Thus it would seem, unlike the Curlew Sandpiper, that the main northward migration route of
Mongolian Plovers continues to include the vicinity of Sungei
Buloh. Further monitoring and implementation of
various habitat management measures at Sungei Buloh may help to reveal the reasons for the general
avoidance of the wetland in favour of the pontoons during the northward
migration period.
Pacific Golden Plover
Pluvialis fulva
Trend: General increase in numbers during both the periods of southward
and northward migration. Counts exceeded 1,000 birds in all years except
2000. A mid-winter peak count of 2000 was recorded in Jan 2005 and this
number is unusual as Jan counts for Pacific Golden Plovers in previous
years had never exceeded 1,000 birds. It could however indicate some
disturbance at the Mandai Mudflats where records
of Pacific Golden Plovers exceeding 2,000 birds at low tide have been
recorded. The southward migration in the same year confirmed this number
with a peak of 1,735 birds counted in Nov 2005. The following year also saw
an unusually high surge of Pacific Golden Plovers in Jan 2006 with a count
of 1,321 birds. AWC counts for Singapore range from 908 to 2416. There
appears to be a trend that more Pacific Golden Plovers are making use of Sungei Buloh. The reasons are
not clear but could be due to the loss of previously derelict land in the Kranji area that had been used by the plovers as a high
tide roost area and which was in 2005 and 2006 being redeveloped resulting
in the plovers moving to Sungei Buloh as the next best high tide roost. The count of
1,081 birds in April 2001 suggests staging during northward migration.
Whimbrel
Numenius phaeopus
Trend: Increased numbers during both
southward and northward migration A maximum count of 442 was obtained. That
count was taken in Nov 2003 and likely involves birds passing through and
making use of Sungei Buloh
as a stop over site. Significant increases in Whimbrels from the preceding months in April 2001 (219
birds), Mar 2002 (215 birds), Mar 2004 (301 birds), Apr 2005 (320 birds)
and Apr 2006 (268 birds) might indicate staging. The high counts of Whimbrels in Mar and April quickly slumps to generally
20 birds or less in early May. Some Whimbrels may
have over summered in Singapore as small numbers were present throughout
May, June and July in most years. First arrivals were noted in late July or
early August and a large influx of birds was noted in September for most
years.
DISCUSSION
This study of shorebird count data from the years 2000 to 2006 has shown
that generally, for counts between September and March (Table 3), over
1,000 shorebirds may be expected at SBWR during the high tide period. From
May to July, only a few species of shorebirds can be found, usually Common
Redshank and Whimbrel with fewer than 30
individuals. From the census data for the seven years period, the shorebird
community at the reserve is composed of seven main species and sixteen
other species that occur in much smaller numbers. These in descending order
of abundance are Common Sandpiper Tringa hypoleucos, Terek Sandpiper Tringa cinerea, Broadbilled Sandpiper Limicola
falcinellus, Ruddy Turnstone Arenaria
interpres, Bar-tailed Godwit Limosa
lapponica, Little Ringed Plover Charadrius dubius, Great Knot
Calidris tenuirostris,
Pintail Snipe Gallinago sterura,
Eurasian Curlew Numenius arquata,
Grey-tailed Tattler Tringa brevipes,
Grey Plover Pluvialis squatarola,
Red-necked Stint Calidris ruficollis,
and Black-tailed Godwit Limosa limosa, Little Curlew Numenius
minutes, Greater Sand Plover Charadrius leschenaultii and Asian Dowitcher
Limnodromus semipalmatus.
Other shorebird species, for example Black-winged Stilt Himantopus
himantopus observed at the reserve in 2005 (Tay
2006) were not recorded during the actual census sessions.
Preliminary data obtained through the counts and observations suggest that
the wetland is favoured by perhaps more than 80% of the Singapore
population of Whimbrel, Mongolian Plover (except
during the northward migration period when they completely avoid the
wetland) and Pacific Golden Plover. The data also suggest that about 50% of
the Common Greenshank and 30% of the Marsh Sandpiper and Common Redshank
population use the wetland as a high tide roost. About 10% of the Curlew
Sandpiper population is thought to use Sungei Buloh as a high tide roost. Further studies would be
required to confirm these hypotheses. More frequent counts over a longer
period would help to establish patterns of seasonal abundance, distribution
and movements of shorebirds in Singapore. A limitation of the data obtained
during the study period is that a substantial influx of passage waders
might last only a few days and might be missed through slipping between
counts that are spaced at wider intervals. Closer-spaced counts during
migration periods would refine our knowledge of the exact magnitude and
timing of passage peaks. The data presented, though limited by resource
constraints, is however sufficient to give an indicative picture of the
seasonal abundance of shorebirds at Sungei Buloh. It is clear that the Sungei
Buloh wetland area is an important site for these
shorebirds. Similar sites in Singapore and around Singapore may possibly
reveal similar species, similar monthly counts and composition of species.
Acknowledgements
The counts were possible through the assistance of the Conservation
Officers and Rangers at Sungei Buloh Wetland Reserve. In particular we would like to
register our appreciation to Abdul Khalid Hamid, Mustaffa Hajar, Charles Lim Sim Moh, Patricia Phua Lee Kheng, Lim Yew Soon,
Jack Wong and the late Ong Hai
Chwee for logistical assistance.
References
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R.K. 2002. Shorebird Monitoring in Sungei Buloh Wetland Reserve in 2001, Wetlands Vol 9, No. 1, Pp13. Publication of SBWR, National Parks
Board, Singapore
Gan, J. and Ramakrishnan,
R.K. 2005. Notes on shorebird numbers in Sungei Buloh Wetland Reserve in 2000 and 2001. The Stilt
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distribution of waterbirds and wetlands in the
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Li, Z.W.D. et. al. 2007. Numbers and distribution of waterbirds
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