Autumn
2003 raptor migration at Chumphon, Thailand: a globally significant
raptor migration watch site.
By Robert DeCandido, Chukiat Nualsri, Deborah Allen and Keith L. Bildstein |
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Note:
This article was originally published in Forktail 20 (2004) the journal
of the Oriental
Bird Club (OBC) and was kindly submitted by Robert
DeCandido.
Please support the OBC's conservation
work by visiting
the OBC website and becoming a member. |
ABSTRACT
Daily counts of migrating raptors were made on 43 days between 27
September and 9 November 2003 near the city of Chumphon in south-east
Thailand. Overall, 170,665 migrating raptors of 15 species were counted
during 378 hours of observation (452 birds/hour).The counts of five
raptor species (Black Baza Avecida leuphotes, Oriental Honey-buzzard
Pernis ptilorhyncus, Eastern Marsh Harrier Circus spilonotus,
Chinese Sparrowhawk Accipiter soloensis and Grey-faced Buzzard
Bustatur indicus) represent some of the highest totals reported
to date. Winds from the north to west and cloud cover were positively
associated with the number of raptors seen. We recommend that counts
be continued at Chumphon in the future and that the site is used to
promote raptor conservation in Thailand. |
INTRODUCTION
Fifty-five species of diurnal raptors occur in Thailand, of
which 41 undertake partial or long-distance movements within
or through the country (Zalles and Bildstein 2000, Robson 2002).
Thailand is an important migration crossroads for east Asian
raptors that over-winter in Malaysia, Singapore, Bali, Sumatra,
and elsewhere in Indonesia. Since the 1960s, biologists have
looked for areas on the Thai-Malay Peninsula from which to count
migrating raptors. Most prior research comes from field studies
in Malaysia (Medway and Nisbet 1965, Wells 1990, Wells 1999).
Raptor migration in Thailand remains largely undocumented (see
Melville and Fletcher 1982, Lekagul et al. 1985, Bijlsma 1996).
In September 1997, large numbers of migrating raptors were observed
by C. Nualsri near the town of Chumphon, south-east Thailand
(Fig. 1). Subsequent observations confirmed significant movements
of raptors through the region each autumn. This important coastal-plain
bottleneck in peninsular Thailand had been previously recognised
from observations made approximately 100 km north of Chumphon
by Melville and Fletcher (1982) and by P. D. Round and others
in 1983–1994 at Kui Buri, c.5 km east of Ban Yang Chum
near the Gulf of Thailand (see Zalles and Bildstein 2000). This
apparently important flyway has not been well studied, however,
and the relative numbers of raptors using it in spring and in
autumn, the origin of the migrants, and their ultimate destinations,
are all largely unknown (Lane and Parish 1991, Zalles and Bildstein
2000, Nijman 2001a). In 2003, we conducted a six-week count
to determine the phenology of these movements including the
numbers of species and individuals involved, together with the
daily and seasonal timing of the migration. |
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Figure 1 : Location of Chumphon, Thailand (1) relative
to other important migration watch sites in East Asia: Beidaihe,
China (2); Uchiyama-toge, Nagasaki, Japan (3);
Kohyamacho, Kagoshima, Japan (4); Miyako Islands
(Ryukyus), Okinawa, Japan (5); Selangor Plain, Malaysia (6);
and Bali Barat National Park, Indonesia (7). |
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METHODS
Chumphon (10o28’N 99o13’E; sea level) is a town (population:
16,000) on the eastern coastal plain of southern Thailand, 460 km
south-west of Bangkok, 550 km north of Malaysia, and 55 km east of
Myanmar. The north-south Bilauktaung range of mountains 35 km to the
west funnels many diurnal bird migrants through this 30-km wide coastal
plain adjacent to the Gulf of Thailand (Wells 1999, Zalles and Bildstein
2000). Migration was observed at a site (10o28.40’N 99o13.26’E)
in an unprotected freshwater marsh 4.6 km east-north-east of Chumphon,
and approximately 2 km north-east of the coastal highway at Ban U-Tapao,
Tha Yang subdistrict, Muang district, Chumphon province. The marsh
is composed primarily of emergent aquatic plants, including sedges
Carex spp., cat-tails Typha spp., and common reed
Phragmites australis.Vegetation averages less than 1.5 m
high, and it does not prevent observation of low-flying raptor migrants.
On fair days, it is possible to see 10 km to the north-east, 3 km
to the east and west, and about 1 km to the south.
The weather in late summer–early autumn is determined by the
interaction between a monsoonal low-pressure system in the Pacific
Ocean to the east, and a high pressure system in the Andaman Sea to
the west. In September and early October, the high pressure system
prevails, and most winds are from the west or north-west. By mid-October,
the low pressure system predominates, and winds are easterly. Heavy
rain is common in mid-October as low pressure replaces high pressure
in the region. The bulk of the migration occurs during the ‘south-west’
(April–October) rather than ‘north-east’ monsoon
(November–January).
We counted migrants from 27 September to 11 November, which correspond
to the peak of the raptor movements in the area. Migrating raptors
were counted by RDC using 10x binoculars, assisted at times by CN
and DA. Count protocols followed those described in Bildstein and
Zalles (1995). Most observations began at 07h00 local time and usually
ended at 17h00. Most raptors (>95%) were readily identified to
species using Porter et al. (1986), Clark (1999), Jeyarajasingham
and Pearson (1999),Wells (1999) and Robson (2002). Weather conditions
(wind speed, barometric pressure, temperature, humidity) were monitored
hourly throughout the day with a hand-held Kestrel 4000 ‘weather
station’ (Nielsen-Kellerman corporation, U.S.A.). Wind direction
was determined with a compass.
Observers scanned primarily north for approaching migrants. An individual
was considered a migrant if it passed north-to-south across an imaginary
east-west line at the watch site, and continued south out of sight.
No attempt was made to determine the relative proportion of males
versus females, or of adults versus immatures.Totals for large flocks
(>300 individuals) of Black Baza Avecida leuphotes, Chinese
Sparrowhawk Accipiter soloensis and Grey-faced Buzzard Bustatur
indicus were estimated to the nearest 25 individuals. |
RESULTS
Table 1 : Raptor species, numbers counted, and seasonal peaks
at Chumphon, Thailand, in autumn 2003. |
Species |
No.
counted (% of total migrants) |
Dates
seen |
Seasonal
peak (highest count) |
OSPREY Pandion haliaetus
BLACK BAZA Aviceda leuphotes
ORIENTAL HONEY-BUZZARD Pernis ptilorhyncus
BLACK KITE Milvus migrans
EASTERN MARSH HARRIER Circus aeruginosus spilonotus
PIED HARRIER Circus melanoleucos
CHINESE SPARROWHAWK Accipiter soloensis
JAPANESE SPARROWHAWK Accipiter gularis
GREY-FACED BUZZARD Butastur indicus
COMMON BUZZARD Buteo buteo
GREATER SPOTTED EAGLE Aquila clanga
BOOTED EAGLE Hieraaetus fasciatus
COMMON KESTREL Falco tinnunculus
EURASIAN HOBBY Falco subbuteo
PEREGRINE FALCON Falco peregrinus
UNIDENTIFIED HARRIER Circus spp.
UNIDENTIFIED ACCIPITER Accipiter spp.
UNIDENTIFIED BUZZARD Buteo spp.
UNIDENTIFIED FALCON Falco spp.
UNIDENTIFIED RAPTORS
Total |
31 (<1%)
68,219 (40%)
15,972 (9%)
124 (<1%)
178 (<1%)
11 (<1%)
57,667 (34%)
5,811 (3%)
14,962 (9%)
10 (<1%)
3 (<1%)
8 (<1%)
4 (<1%)
3 (<1%)
8 (<1%)
66 (<1%)
1,168 (1%)
5 (<1%)
4 (<1%)
6,411 (4%)
170,665 |
5 Oct–9 Nov
21 Oct–9 Nov
10 Sep– 9 Nov
27 Sep–9 Nov
27 Sep–9 Nov
27 Sep–2 Nov
27 Sep–9 Nov
9 Sep–9 Nov14 Oct–9 Nov
8 Oct–9 Nov
18 Oct–23 Oct
10 Oct–5 Nov
18 Oct–23 Oct
15 Oct–24 Oct
8 Oct–18 Oct |
18 Oct (6)
23 Oct (42,046)
1 Oct (3,021)
10 Oct (29)
23 Oct (25)
11 Oct (10,389)
23 Oct (606)
23 Oct (9,985)
23 Oct (56,101) |
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In
total, 170,665 raptors of 15 species were counted migrating during
378 hours of observation (averaging 452 birds/hour;Table 1). Black
Baza was the commonest migrant (68,219 individuals), representing
40% of the 163,020 individuals identified to species (Table 1). The
largest flock of this species, estimated at 1,300 birds, passed on
23 October. Chinese Sparrowhawk (57,667 individuals) made up 34% of
all individuals identified, with 550 individuals in one flock on 11
October. We also observed large numbers of Grey-faced Buzzard (14,962
individuals; 9%; largest flock = 500 individuals on 23 October) and
Oriental Honey- Buzzard Pernis ptilorhyncus (15,972 individuals;
9%; largest flock = 91 individuals on 7 October).
The highest single day count was 56,101 individuals of ten species
on 23 October (Fig. 2). A peak of 11 species was observed on 18 October.There
were differences between species in their seasonal pattern of migration
(Fig. 3). Of the five commonest species, Chinese Sparrowhawk and Oriental
Honey-buzzard migrated through the area primarily before mid- October,
Grey-faced Buzzard and Black Baza migrated primarily in late October,
and Japanese Sparrowhawk Accipiter gularis migrated through
the area throughout the autumn (Fig. 3).
Raptors at Chumphon typically migrated throughout the day, sometimes
from shortly after 07h00 until shortly before 18h00 (Fig. 4). On most
days, movements of Chinese Sparrowhawk and Grey-faced Buzzard peaked
at 09h00–10h00. Oriental Honey-buzzard migration peaked at 10h00–11h00.
About half of all raptors (53%) were seen from 09h00 to12h00 (Fig.
4). On most days, counts decreased thereafter until 15h00–16h00,
when they again increased. Most of the migrants (72%) were seen when
cloud cover exceeded 70%. Between 12h00 and 15h30, raptors frequently
flew at heights above 600–800 m, especially if winds were <8km/hour.
Entire flocks of certain species (Chinese Sparrowhawk, Grey-faced
Buzzard), and individuals of other species (Oriental Honeybuzzard,
Japanese Sparrowhawk) sometimes disappeared into the bases of clouds
when they soared in thermals. At 19h25 on 1 October 2003, CN observed
a flock of about 50 Chinese Sparrowhawks entering a night-time roost
in a coconut Cocos nucifera grove near the watch site. Several
species, including Black Baza, Chinese Sparrowhawk, and Japanese Sparrowhawk
roosted in coastal mangrove forests 10–15 km north of the site.
We considered four species (Black Baza, Oriental Honey-buzzard, Chinese
Sparrowhawk and Greyfaced Buzzard) to be obligate flocking migrants
at the site (sensu Kerlinger 1989). We also observed mixedspecies
flocks of Grey-faced Buzzard and Black Baza, and of Japanese and Chinese
Sparrowhawk. Individuals of several other species (e.g. Osprey Pandion
haliaetus, Black Kite Milvus migrans and Greater Spotted
Eagle Aquila clanga) were sometimes seen in groups of two
or more individuals. Several researchers (Ash 1993, Wells 1999, Nijman
2001b, Robson 2002) have noted flocks of Japanese Sparrowhawk in South-East
Asia, but we did not see single-species flocks of this species at
Chumphon.
More raptors were counted at the site on winds from the west or north-north-west
than the east or south (P² = 41.7, P<0.05). From 27 September
to 25 October, winds were typically light to moderate for the entire
day. Later in the season, early morning westerly or variable winds
shifted to on-shore, easterly winds by about 10h00. Raptors were then
seen primarily flying north-to-south-west of the site, and after noon
few raptors were observed passing over the site itself.
Three additional raptor species (Black-shouldered Kite Elanus
caeruleus, Brahminy Kite Haliastur indus, and White-bellied
Sea Eagle Haliaeetus leucogaster) were resident in and around
Chumphon and were not counted. Non-raptors seen migrating, or apparently
migrating, at the watch site included Little Cormorant Phalacrocorax
niger, Grey Heron Ardea cinerea, Purple Heron Ardea
purpurea, Oriental Pratincole Glareola maldivarum, Grey-headed
Lapwing Vanellus cinereus, Pale-capped Pigeon Columba
punicea, House Swift Apus affinis, Asian Palm Swift
Cypsiurus balasiensis, Fork-tailed Swift Apus pacificus,
Blue-throated Beeeater Merops viridis, Blue-tailed Bee-eater
Merops philippinus, Barn Swallow Hirundo rustica,
Red-rumped Swallow Hirundo daurica, Sand Martin Riparia
riparia, Ashy Minivet Pericrocotus divaricatus and Black
Drongo Dicrurus macrocercus (see DeCandido et al.
2004). |
Figure
2 : Daily totals of raptors counted on migration at Chumphon,Thailand,
autumn 2003.
Figure 3(a) : Number of Black Baza counted at Chumphon,Thailand,
in autumn 2003.
Figure 3(b) : Number of Oriental Honeybuzzard counted
at Chumphon,Thailand, in autumn 2003.
Figure 3(c) : Number of Chinese Sparrowhawk, counted
at Chumphon,Thailand, in autumn 2003.
Figure 3(d) : Number of Japanese Sparrowhawk, counted
at Chumphon,Thailand, in autumn 2003.
Figure 3(e) : Number of Grey-faced Buzzard, counted
at Chumphon,Thailand, in autumn 2003.
Figure 4 : Pattern of raptor migration through the
day (birds/hour) at Chumphon, Thailand, in autumn 2003. |
DISCUSSION
Our counts demonstrate a significant autumn movement of soaring raptors
at Chumphon, Thailand. The number of raptor species observed (15),
the number of individuals counted (170,665), and the average number
of raptors counted per hour (452) are the highest totals reported
to date in South-East Asia. The numbers of five species (Black Baza,
Oriental Honey-buzzard, Eastern Marsh Harrier, Chinese Sparrowhawk,
and Grey-faced Buzzard) appear to be among the highest single-season
totals reported in Asia (Medway and Nisbet 1964, Lin and Lin 1986,
Severinghaus 1991, Ash 1993, Kugai 1996, Chong 2000, Nitani 2000,
Williams 2000, Nijman 2001b, Tordoff 2002; see Table 2). Based on
our observations, we estimate that as many as 500,000 raptors may
migrate south over Chumphon each year between August and early
December. This makes Chumphon a watch site of global significance
(Yosef et al. 2000, Zalles and Bildstein 2000). |
Species |
Max.
count |
Year |
Location |
Source |
BLACK BAZA Avecida leuphotes |
68,219 |
2003 |
Chumphon,Thailand |
This study |
ORIENTAL
HONEY-BUZZARD Pernis ptilorhyncus |
121,000 |
1963 |
Selangor
Plain, Malaysia |
Medway
& Nisbet (1964),Wells (1999) |
EASTERN
MARSH HARRIER Circus aeruginosus spilonotus |
576 |
1986 |
Beidaihe,
China |
Williams
(2000) |
CHINESE
SPARROWHAWK Accipiter soloensis |
439,276 |
1999 |
Uchiyama-toge,
Nagasaki, Japan |
Nitani
(2000), Chong (2000) |
JAPANESE
SPARROWHAWK Accipiter gularis |
7,835 |
1984 |
Bali
Barat, Indonesia |
Ash
(1993) |
GREY-FACED
BUZZARD Butastur indicus |
31,784* |
1999 |
Kohyamacho,
Kagoshima, Japan |
Nitani
(2000), Chong (2000) |
|
*Unpublished
data indicate that a higher count was made at the Miyako islands (Ryukyus),
Okinawa, Japan: 53,575 individuals in autumn 1980; data from 1973–2003
give an annual mean of 27,859 individuals (Y. Nitani in litt. 2004).
Small numbers of two other raptors (nine Steppe Eagles Aquila
nipalensis and two Imperial Eagles Aquila heliaca) were
seen migrating in early November at a location c.8 km west of the
site (not included in Table 1). Further research may determine if
several other raptor species that are regarded as migrants in Thailand
(Hen Harrier Circus cyaneus,Western Marsh Harrier C.
aeruginosus aeruginosus, Shikra Accipiter badius and
Eurasian Sparrowhawk A. nisus) also regularly pass through
the area.
The raptors counted at Chumphon are thought to follow at least two
migration routes in East Asia: (a) an Eastern Inland Corridor that
extends from southeastern Siberia through eastern China and Indochina
(Laos, northern Vietnam, northern Thailand), south through the Thai-Malay
Peninsula; and (b) a Coastal Pacific Corridor that extends from north-eastern
Siberia, Amurland, and Ussuriland through coastal China, south into
Indochina and the Thai-Malay Peninsula (McClure 1998, Zalles and Bildstein
2000). Movements along these corridors are poorly understood, and
additional study is needed to determine the routes used by different
raptors in the Far East (Ellis et al. 1990, Lane and Parish
1991, Severinghaus 1991, Ash 1993, Chong 2000, Nitani 2000, Williams
2000, Nijman 2001a,Tordoff 2002). Satellite-tracking of two Oriental
Honey-buzzards in autumn 2003 showed that they left their breeding
grounds in Japan in mid-September, crossed to mainland China and headed
south-west across Indochina, then south through the Thai-Malay Peninsula
to Sumatra (H. Higuchi in litt. 2004). Further studies may reveal
the extent to which outbound raptors including Oriental Honey-buzzard,
Chinese Sparrowhawk and Grey-faced Buzzard, follow the Oceanic Pacific
Corridor, before heading west to the mainland, and south into Malaysia
and Indonesia.
Weather conditions had a major influence on the number of raptors
migrating. Significantly more raptors were seen when winds were from
the northwest quadrant than when winds were from the south-east quadrant.
Raptors seemed to ‘drift’ to the coast with westerly winds
when skies were overcast and when strong thermals were lacking. With
moderate westerly winds, as many as 10% of the migrants passed approximately
2 km to the east of the site along the Gulf of Thailand. On 23 October,
we counted 56,101 migrants during overcast skies and light to moderate
west to north-west winds. On that day the area <7 km north and
west of the watch site was free of precipitation, but it was raining
throughout much of central and northern Thailand. Although steady
rain at the watch site ended raptor migration there, we believe that
local rains simply diverted migrants around the precipitation cell.
Observers in the Neotropics have also noted migration in light or
intermittent rain and overcast skies (Bildstein and Saborio 2000). |
RECOMMENDATIONS
The raptor migration at Chumphon affords an exceptional opportunity
for research and education. We recommend a season-long autumn count
by experienced observers from mid-August to late November, as well
as exploratory partial season spring counts in mid- March through
mid-May. Several (3–4) observers would be needed in order to
reduce observer fatigue. Training of local people to assist with counts
is needed. Consideration should be given to a coordinated transect
count in the region, including searching for large overnight roosts.
There is no comprehensive guide to flight identification of raptors
for this part of the world, and we suggest that printed and on-line
guides to the different raptors of East Asia be developed as quickly
as possible. A poster depicting raptor diversity in Thailand and South-East
Asia could serve as a keystone visual aid providing information about
Asian raptors. A children’s colouring book of the common birds
of Thailand with basic information about urban and suburban raptors
would create interest at the grassroots level. |
ACKNOWLEDGEMENTS
We sincerely appreciate the encouragement and thoughtful advice of
Phil Round of Mahidol University. Uthai Treesucon of Bangkok provided
many helpful ideas and suggestions to the raptor watch team. We thank
Hiroyoshi Higuchi of the University of Tokyo for sharing some unpublished
information. Yasunori Nitani of the Asia Raptor Research and Conservation
Organization (ARRCN) provided migration count data for Chinese Sparrowhawks
and Greyfaced Buzzards in Japan. Anne Arrowsmith designed the map.
We deeply appreciate the kindness shown to us by our colleagues of
the Malaysian Nature Society including Laurence and Audrey Poh, Cheang
Kum Seng, Liew Siew Lan and Ooi Beng Yean, Regina Anthony and Chiu
Sein Chong as well as Lim Aun Tiah and Lim Kim Chye. Desmond Allen
provided GPS coordinates of the site. David Wells read a version of
this manuscript and provided helpful comments. Those wishing to observe
raptor migration at Chumphon should contact Chukiat Nualsri (bntern@chaiyo.com)
for details about how to reach the watch site, and the annual Raptor
Watch festival usually held in the second week of October. Our research
was supported by grants from the Bobolink Foundation and the Oriental
Bird Club, and by a Hawk Mountain Sanctuary Project Soar Award. This
is Hawk Mountain Sanctuary Contribution to Conservation Science number
108. |
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Kindly
submitted by:
Robert DeCandido, Acopian Center for Conservation Learning,Hawk
Mountain Sanctuary, 410 Summer Valley Road, Orwigsburg, Pennsylvania
17961 U.S.A. Correspondence: 1831 Fowler Avenue,The Bronx, New York
10462-3708. Email: rdcny@earthlink.net
Chukiat Nualsri,Thayang Administrative Organization, 135-1 Kromluang
Chumphon Road, Muang Chumphon 86000,Thailand. Email: bntern@chaiyo.com
Deborah Allen,The Linnaean Society of New York, P.O. Box 1452 Peter
Stuyvesant Station, New York 10009, U.S.A. Email: dallenyc@earthlink.net
Keith L. Bildstein, Acopian Center for Conservation Learning,Hawk
Mountain Sanctuary, 410 Summer Valley Road, Orwigsburg, Pennsylvania
17961 U.S.A. Email: bildstein@hawkmtn.org |
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