and abundance of Grey-faced Buzzards Butastur indicus and
other raptors on northbound migration in southern Thailand, spring
By Robert DeCandido
& Chukiat Nualsri
This article was originally published in Forktail 25 (2009) the journal
of the Oriental
Bird Club (OBC) and was kindly submitted by Robert
Please support the OBC's conservation
work by visiting
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We provide the first extensive migration data about northbound migrant
raptors in Indochina. Daily counts were made at one site (Promsri
Hill) in southern Thailand near the city of Chumphon, from late February
through early April 2007–08. We identified 19 raptor species
as migrants, and counted 43,451 individuals in 2007 (112.0 migrants/hr)
and 55,088 in 2008 (160.6 migrants/hr), the highest number of species
and seasonal totals for any spring raptor watch site in the region.
In both years, large numbers of raptors were first seen beginning
at 12h00, and more than 70% of the migration was observed between
14h00 and 17h00 with the onset of strong thermals and an onshore sea
breeze from the nearby Gulf of Thailand. Two raptor species, Jerdon’s
Baza Aviceda jerdoni and Crested Serpent Eagle Spilornis
cheela, were recorded as northbound migrants for the first time
in Asia. Four species composed more than 95% of the migration: Black
Baza Aviceda leuphotes (mean 50.8 migrants/hr in 2007–08),
Grey-faced Buzzard Butastur indicus (47.5/hr in 2007–08),
Chinese Sparrowhawk Accipiter soloensis (22.3/hr in 2007–08),
and Oriental Honey-buzzard Pernis ptilorhynchus (7.5/hr in
2007–08). Most (>95%) Black Bazas, Chinese Sparrowhawks and
Grey-faced Buzzards were observed migrating in flocks. Grey-faced
Buzzard flocks averaged 25–30 birds/ flock. Seasonally, our
counts indicate that the peak of the Grey-faced Buzzard migration
occurs in early to mid-March, while Black Baza and Chinese Sparrowhawk
peak in late March through early April. Oriental Honey-buzzard migrated
throughout the observation period, with a peak in mid- to late March.
In the last decade, there has been increasing interest in raptor
migration in Indochina (DeCandido et al. 2008). Scientists
investigating this East Asian Continental Flyway have used satellite
telemetry to follow Oriental Honey-buzzards Pernis ptilorhynchus
to determine migration timing, stopover sites, and differences between
routes selected by males vs females vs immatures (Higuchi et
al. 2005, Shiu et al. 2006). Others have established
‘watch sites’ to assess the numbers of migrants and
species seen in Thailand and Malaysia (DeCandido et al. 2004,
2006, Lim and Cheung 2007, 2008). Yet our knowledge of raptor migration
through Indochina, particularly during northbound migration, is
limited. Here we provide the first extensive spring migration data
for the region, including the number of raptor species and individuals
involved, and their seasonal timing while heading north through
Figure 1. Map of south-central Thailand showing
the Promsri Hill raptor migration watch site in relation to Chumphon
City, the main road (Route 4), and the autumn raptor watch site
used since 2000.
March 2003, large numbers of northbound migrating raptors were first
observed by CN west of the town of Chumphon on the Isthmus of Kra
in southern Thailand (Fig. 1). Periodic observations by CN in February
through April 2004–2006 confirmed a significant migration pathway
in the area. These raptors are returning to breed in eastern Russia
and southern China, west through parts of Siberia, Nepal, Mongolia
and Korea, as far east as Japan (Fig. 2).
2. Map of East Asia showing the two primary continental
spring raptor migration count sites: (1) Promsri Hill (Thailand)
and (2) Tanjung Tuan (West Malaysia). Also shown in the primary
oceanic migration corridor of northbound Grey-faced Buzzards in
spring: (A) Philippine Islands, (B) Taiwan, and (C) Japan.
were particularly interested in documenting the abundance and passage
timing of Grey-faced Buzzard Butastur indicus. Previous
research focused on the segment of the population that migrates
by island-hopping through the East Asian Oceanic Flyway via Japan
and Taiwan to winter in the Philippine Islands to Sulawesi and New
Guinea (Kugai 1996, Shiu et al. 2006, Germi et al.
2009). However, little is known about the continental migrant population
we observed in spring 2007–08. Though Grey-faced Buzzards
are common October migrants in Thailand (DeCandido et al.
2004), further south in the Thai-Malay Peninsula this species is
a rare to uncommon migrant in either season in Singapore and at
Tanjung Tuan on the west coast of Malaysia (Wells 1999).
From a broader
perspective, we had specific research questions about spring raptor
migration in South-East Asia. (1) What raptor species migrate through
the region in spring vs autumn? (2) What is the daily pattern of
raptor migration at our Promsri Hill watch site in southern Thailand:
is there a late morning peak with declining numbers seen for the
remainder of the day, similar to that observed during southbound
migration in autumn 2003 at a watch site some 20 km east-south-east
(see DeCandido et al. 2004)? (3) What is the seasonal pattern
of spring migration for raptors commonly seen here including Black
Baza Aviceda leuphotes, Oriental Honey-buzzard, Chinese
Sparrowhawk Accipiter soloensis and Grey-faced Buzzard?
(4) How do weather variables, such as wind direction, affect the
migration observed at our watch site? By addressing such questions,
we hope to provide information to biologists, conservationists and
birdwatchers interested in understanding a crucial time in the life
history of Asian migratory raptors.
In late February through early April 2007–08, we made daily
counts of migrant raptors, two bee-eater species and other land
birds from a site 15 km west of Chumphon City (10°28’N
99°13’E, sea-level), known locally as Promsri Hill or
Khao Klai. The watch site (10°30’N 99°04’E)
sits on the crest of a hill, c.5 km west of the main N–S highway
(Phetkasem Road, Highway 4) and 475 km south-west of Bangkok (Fig.
1). The site afforded an unobstructed 360º view of northbound
migrants. The hill is the southern terminus of a low S–N ridge
on military land, and is accessible by permit only. Much of this
ridge is comprised of seasonal grasses, scrub and second growth,
on average less than 2 m in height. Most of the surrounding area
and nearby hills have been developed for pasture and agriculture
(banana, oil palm), with second-growth forest occupying perhaps
the upper 10% of these hills. On clear days it was possible to see
east c.25 km to the Gulf of Thailand; south c.5 km to a tall hill
(Khao Thai Dang); west c.10 km to a hill (Khao Nam Lod) that is
part of a south to north ridge system; and north c.3 km.
migration watch site (Promsri Hill) is c.15 km west-north-west of
the autumn watch site used since 2000. Observations by CN each spring
from 2004 through 2006 suggested that few migrants pass the vicinity
of the autumn watch site. Instead, Promsri Hill was selected for
spring migration research because it afforded the best combination
of height above the surrounding lowlands, proximity to significant
numbers of migrants, and ease of access. Earlier in the day, from
about 08h00 until 10h00, the migration is best observed at the intersection
of Highway 4 and Highway 41 (Fig. 1). However, overall more migrants
pass to the west of this intersection, and these are more easily
seen from Promsri Hill.
In both years,
we measured hourly the wind speed and direction, temperature, humidity
and barometric pressure with a hand-held weather station (Kestrel
4000, Nielsen- Kellerman Corporation, U.S.A.). Wind direction was
determined with a compass. Weather conditions typically were hazy
and humid with little wind in the morning until 09h00, then becoming
clear with cumulus clouds. Until c.09h00 to as late as c.11h00 each
day, light westerly winds (less than 10 km/hr) prevailed, then switching
easterly due to the interaction of the north-east low pressure monsoon
(Guo et al. 2002) combined with a sea-breeze from the nearby
Gulf of Thailand (Khedari et al. 2002). However, the exact
timing of the wind switch varied greatly in 2007 compared to 2008,
as did the intensity of these easterly winds.
counted with binoculars by RDC with help from CN. Others visited
the site after 14h00 most days and helped to locate distant flocks
of migrants. We made daily counts during two spring seasons: in
2007, from 28 February through 3 April (35 days; 388 hours of observation);
and in 2008, from 28 February through 31 March (32 days; 343 hours
of observation). Observations usually began by 07h00 local time,
and ended by 18h30 each day. During inclement weather such as thunderstorms,
we remained in the area of the watch site looking for migrants.
For one day in 2008 (10 March), when it rained all day, no count
was made. CN also made periodic observations of up to three days
per week from late January through February 2003–2006, and
again in April to mid-May 2009.
To locate migrating
raptors, observers scanned from the west-south-west to the east.
To identify migrants, we consulted Lekagul et al. (1991),
Wells (1999), Herremans and Louette (2000), Robson (2002) and Kasordorkbua
et al. (2008). Scientific names follow Inskipp et al.
(1996, 2001). Raptors were considered migrants if they passed
south to north across an imaginary east–west line at the watch
site, and continued north and out of sight. We did not attempt to
age or sex migrants. We defined a flock of migrating raptors as
any group of at least two individuals passing the watch site within
c.3 minutes of one another. Most raptors were observed migrating
within 3 km of the watch site. Beyond c.5 km it was very difficult
to detect and identify a lone migrant, or small flocks of certain
species such as Chinese Sparrowhawk.
the daily and seasonal pattern of raptor migration, we pooled the
data of all individuals we counted at the site, including migrants
we could not identify to species. To determine the seasonal peak
for the commonest raptor species in 2007 and 2008, we used the highest
ten-day average in each year. In Table 1, for the highest daily
count of individuals for species for which we saw only one migrant
on two different dates, we chose the first date as the peak. We
also calculated a median date (the day at which 50% of the individuals
of a particular species had been counted) of peak passage for the
four commonest raptors by pooling 2007–08 data for each of
that more raptors would pass the watch site when winds had an easterly
component (NE to SE), than when winds were from other directions,
usually west to south. We used a chi-square test with one degree
of freedom (Preacher 2001) to analyse the effect of wind direction
on the number of raptors passing the watch site when winds from
these two general directions prevailed.
In spring 2007–08, a total of 98,539 raptors of 19 species
was counted, averaging 112.0 migrants/hr in 2007, and 160.6 migrants/hr
in 2008 (Table 1). Four species comprised >95% of the migration
in 2007–08: Black Baza (38%), Grey-faced Buzzard (35%), Chinese
Sparrowhawk (17%) and Oriental Honey-buzzard (6%). Three of these
were primarily seen in single-species flocks: Black Baza, Grey-faced
Buzzard and Chinese Sparrowhawk. In spring 2008, we counted 8,954
(63%) more Black Bazas and noted three additional raptor species
vs our spring 2007 count (Table 1).
1. Raptor species, numbers counted, and seasonal peaks
at Promsri Hill, Chumphon, Thailand, in spring 2007–2008.
counted (% of total migrants)
peak (highest count)
OSPREY Pandion haliaetus
23 Mar 08 (8)
Mar 08 (4,334)
BAZA Aviceda jerdoni
Mar 07 (1)
HONEY-BUZZARD Pernis ptilorhyncus
Mar 07 (285)
Mar 08 (4)
MARSH HARRIER Circus aeruginosus spilonotus
Mar 08 (2)
SPARROWHAWK Accipiter soloensis
Mar 07 (1,391)
SPARROWHAWK Accipiter gularis
Mar 08 (169)
Mar 08 (1)
BUZZARD Butastur indicus
Mar 08 (3,126)
BUZZARD Buteo buteo
SERPENT EAGLE Spilornis cheela
Mar 07 (4); 1 Mar 08 (4)
SPOTTED EAGLE Aquila clanga
Mar 08 (2)
EAGLE Hieraaetus fasciatus
Mar 08 (1)
KESTREL Falco tinnunculus
Mar 08 (1)
HOBBY Falco subbuteo
HOBBY Falco severus
Mar 08 (1)
FALCON Falco peregrinus
Mar 07 (1); 29 Mar 08 (1)
Mar 08 (258)
Mar 08 (5,805)
both years, large numbers of raptors began to pass the watch site
beginning at 12h00 (Fig. 3), with most (>70%) migrants observed
between 14h00 and 17h00. From c.08h00 to 09h30 the migration passed
c.5 km to the east of Promsri Hill following the route of the main
road (Highway 4), and gradually shifted further west throughout
the morning (Fig. 1). In 2007, the highest hourly count (1,686)
occurred between 14h00 and 15h00 on 29 March. In 2008, the highest
hourly count (2,768) occurred between 16h00 and 17h00 on 30 March.
Large numbers of Black Bazas accounted for these high totals. In
2007–08, significantly greater numbers of migrant raptors
passed the watch site when winds were easterly (NE, E or SE) than
when winds were from other directions (?² = 1190.5, p <
0.05, df = 1).
Figure 3. Mean number of raptors counted per hour
at Promsri Hill, Thailand during spring 2007–08.
4 shows the daily totals of the four commonest migrant raptor species
observed at Promsri Hill in spring 2007–08. For Black Baza
in 2007–2008, we counted 50.8 migrants/hr. The two-year median
date for peak passage was 25 March. In 2007, the peak ten-day migration
period for Black Baza occurred from 21 March to 30 March (Fig. 4a),
averaging 932.0 migrants/day and 80.0 migrants/hr. In 2008, the
peak time-frame also occurred from 21 March to 30 March (Fig. 4a),
averaging 1,954.5 migrants/day and 176.9 migrants/hr. The highest
single-day count of migrating Black Bazas was 4,334 on 24 March
2008 (Table 1). Fewer than 100 total migrants of this species were
observed at Promsri Hill after 5 April in 2009, and we consider
their migration complete by mid-April in southern Thailand.
Honey-buzzard in 2007–2008, we counted 7.5 migrants/hr. The
two-year median date for peak passage was 19 March. In 2007, the
peak ten-day migration period occurred from 19 March to 28 March
(Fig. 4b), averaging 161.8 migrants/day and 13.9 migrants/ hr. In
2008, the migration peak occurred from 11 March to 20 March (Fig.
4b), averaging 157.6 migrants/day and 14.5 migrants/hr. The highest
single-day count of migrating Oriental Honey-buzzards was 285 on
25 March 2007 (Table 1). In past years, the earliest birds were
seen on 1 February 2004 (CN). In observations during April through
mid-May 2009, CN observed up to 100 Oriental Honey-buzzards per
day in migration as late as 8 May.
Sparrowhawk in 2007–2008, we counted 22.3 migrants/hr. The
two-year median date for peak passage was 26 March. In 2007, the
peak ten-day migration period for this species occurred from 21
March to 30 March (Fig. 4c), averaging 447.5 migrants/day and 38.4
migrants/hr. In 2008, the peak time-frame also occurred from 21
March to 30 March (Fig. 4c), averaging 739.0 migrants/day and 66.9
migrants/hr. The highest singleday count of migrating Chinese Sparrowhawks
was 1,391 on 30 March 2007 (Table 1). In early April 2009, totals
of 200–300 were seen in migration per day. However, numbers
declined rapidly after 5 April, although singles passed the watch
site through early May (CN).
Figure 4. Number of migrant individuals counted
per day during spring 2007–08 at Promsri Hill, Thailand. (a)
Black Baza, (b) Oriental Honeybuzzard, (c) Chinese Sparrowhawk,
(d) Grey-faced Buzzard.
Grey-faced Buzzard in 2007–2008, we counted 47.5 migrants/hr.
The two-year median date for peak passage was 13 March. Over 99%
of all Grey-faced Buzzards were observed migrating in flocks (789
flocks in 2007; 864 in 2008). Most flocks numbered 2–25 individuals
(Fig. 5). In 2007, the peak ten-day migration period occurred from
5 March to 14 March (Fig. 4d), averaging 1,364 migrants/day and
120.2 migrants/hr. During this time, the mean flock size (N = 457
flocks) was 27.6 birds (Standard Deviation [SD] = 26.6). In 2007,the
largest flock (175) passed the watch site between 15h00 and 16h00
on 8 March. In 2008, the peak migration timeframe for this species
occurred from 11 March to 20 March, averaging 1,389.4 migrants/day
and 128.0 migrants/hr. For these ten days, the mean flock size (N
= 551 flocks) was 25.0 birds (SD = 56.3). In 2008, the largest flock
(182) passed the watch site between 10h00 and 11h00 on 13 March.
The highest single-day count was 3,126 on 15 March 2008 (Table 1).
Compared to the hourly pattern of raptor migration at the watch
site (Fig. 3), a greater proportion of Grey-faced Buzzards (Fig.
6) were counted earlier in the day (08h00 to 11h00). In early April
2009, few (<25 total) Grey-faced Buzzards were counted, and none
were seen after 5 April 2009 (CN).
We counted fewer
than ten individuals of six additional species: Jerdon’s Baza
Aviceda jerdoni, Common Buzzard
Buteo buteo, Booted Eagle Hieraaetus pennatus,
Eurasian Hobby Falco subbuteo, Oriental Hobby Falco
severus and Peregrine Falcon Falco peregrinus (Table
1). Individuals of these species are difficult to detect if they
are part of a larger mixed-species group, especially if flying at
moderate to high altitudes. Two raptor species, Shikra Accipiter
badius and Common Kestrel Falco tinnunculus, were
winter residents and/or breeders in the area of Promsri Hill, so
we regarded most sightings of these species to be local rather than
Figure 5. Number and average size of Grey-faced
Buzzard flocks counted during migration in spring 2007–08 at Promsri Hill,
Mean number of Grey-faced Buzzards counted per hour during spring 2007–08 at Promsri Hill, Thailand.
Our research in spring 2007–08 at Promsri Hill documents a
significant northbound migration of at least 19 raptor species through
southern Thailand (Table 1). Our totals represent the highest numbers
of species and individuals reported for any spring watch site in Indochina. We identified two
species as migrants for the first time during spring in Asia: Jerdon’s
Baza and Crested Serpent Eagle. Our counts of Black Baza and Grey-faced
Buzzard are the highest reported to date on the mainland during
spring migration. We also observed more species on migration in
this study than we did in our previous research (16 spp.) during
southbound migration in autumn 2003 (DeCandido et al. 2004).
species accounted for >95% of the migration in spring 2007–08:
Black Baza (38%), Grey-faced Buzzard (35%), Chinese Sparrowhawk
(17%) and Oriental Honey-buzzard (6%). Based upon these data, as
well as on observations made by CN in April to mid-May 2009, we
suggest that most Black Bazas and Chinese Sparrowhawks migrate through
southern Thailand in the last ten days of March and the first few
days of April, and their migration is virtually complete in southern
Thailand by 15 April. Japanese Sparrowhawk Accipiter gularis
is a common southbound migrant in the area of Chumphon (DeCandido
et al. 2004), and observations by CN in 2004–06 suggest
that its spring migration through this area of Thailand occurs primarily
from late January to late February.
counts are consistent from year to year, averaging 17,372/spring
(Table 1), with most migrants travelling in flocks of <25 (Fig.
5). In both 2007 and 2008, our counts of Grey-faced Buzzard exceed
the autumn 2003 count (DeCandido et al. 2004). At Promsri
Hill, we observed a mid-morning (08h00–11h00) peak in the
flight (Fig. 6) suggesting that many Grey-faced Buzzards began their
migration in the area, possibly after roosting nearby overnight.
Seasonally, the first Grey-faced Buzzards have been observed as
early as 1 February 2005 (CN). Grey-faced Buzzard migration peaks
in early to mid-March, c.5–20 March each year (Fig. 4d), and
is completed by 10 April in southern Thailand. In Taiwan, part of
the East Asian Oceanic Flyway (Fig. 2), data show that Grey-faced
Buzzard migration peaks between 15 March and 30 March each spring
(C. Chen 2006). Only one count location in Asia (at BaGuaShan, Taiwan),
has reported more spring migrant Grey-faced Buzzards (c.22,000/spring)
than our 2007–08 counts (see C. Chen 2006, Y.-J. Chen 2006).
Further south, fewer than 100 Grey-faced Buzzards are counted annually
in northbound migration at Tanjung Tuan, Malaysia (DeCandido et
al. 2006, Lim and Cheung 2007, 2008), and this species is not
seen every year in Singapore (Ow Yong 2008). We propose that the
primary wintering area of the continental migratory population of
Grey-faced Buzzards is in the highlands of northern Malaysia and
Our counts of
migrant Oriental Honey-buzzards (2,751/spring) are low compared
with recent spring counts at Tanjung Tuan, where c.24,000 were counted
in 2007 (Lim and Cheung 2007), and 32,000 in 2008 (Lim and Cheung
2008). There, the peak of the migration is in mid-March (DeCandido
et al. 2006). Lim and Cheung (2008) report the highest
daily counts occurred on 11 March 2008 (4,102) and 14 March 2008
(4,367). At Promsri Hill, Oriental Honey-buzzards peak around 10–
25 March (Fig. 4b), suggesting that some of these migrants also
passed through the area of Tanjung Tuan, and many probably migrate
to our west, perhaps even through Myanmar. Migrant Oriental Honey-buzzards
continue to pass Promsri Hill in small numbers (up to 100/day) in
April to mid-May, and future studies might reveal how late into
May migrants of this species pass through southern Thailand.
wind direction and speed, played the major role in the number of
migrants we counted in spring 2007–08. Significantly more
raptors were counted when winds had an easterly component from the
Gulf of Thailand than when winds were from other directions. Easterly
winds were strongest from mid- to late afternoon, as thermal activity
increased, and were associated with the greatest number of raptors
seen (Fig. 3). These onshore winds combined with additional easterly
winds generated by the north-east low-pressure monsoon (Guo et
al. 2002, Khedari et al. 2002), causing migrants to
drift inland toward the watch site, particularly in spring 2008.
By comparison, when easterly winds failed on 17–18 March 2007,
more than 3,400 raptors were counted in migration at a site c.5
km to the east of Promsri Hill along the main road (Route 4), while
less than 100 raptors passed the main watch site (K. Termtanan in
litt. 2007). The diurnal pattern of spring raptor migration
at Promsri Hill peaked several hours later in the day than the mid-morning
peak we recorded at a nearby coastal watch site east of Chumphon
during autumn 2003 (DeCandido et al. 2004). There, most
raptors were observed when winds had a westerly component (DeCandido
et al. 2004).
Given the importance
of the area for understanding patterns of northbound raptor migration
in Indochina, we recommend further research at the site since we
observed important differences in the pattern of the migration just
between spring 2007 and 2008. During our study, we received information
that large raptors, including Oriental Honey-buzzards, had been
shot in the area of the watch site. Educational outreach, particularly
bilingual colouring books of local birds for children, and on-line
brochures of the migrants for adults (see van Kam et al.
2008), would greatly benefit raptor conservation locally and regionally.
We dedicate this paper to Asian raptor scholar, Jean-Marc Thiollay.
Our research in Thailand was made possible with strong support from
our family and friends including Aree Nualsri and son, Narathip; Deborah
Allen; Pattaporn Charoenosot; and the Promsri family including Taek,
Jee, Apple, Side, Ying and Ning. Chatuphon Sawasdee of the Thai Raptor
Group designed the two maps. We benefited greatly from the advice
and participation of many colleagues, particularly Nurak Isarasena
and Edmund Pease, Chaiyan Kasorndorkbua, Chaiwat Chinuparawat, Uthai
Treesucon, William Duckworth and Philip Round. In Chumphon, Captain
Narong Pethploy of the Military Police Company, Khetudomsak Camp,
Chumphon Military Province, graciously gave permission and provided
assistance to make Khao Klai (Promsri Hill) a wonderful observation
site in spring 2007–08. Laurie Goodrich of the Hawk Mountain
Sanctuary made many helpful comments that significantly improved this
manuscript. Two referees, Keith Bildstein and Francesco Germi, contributed their knowledge and expertise. We also wish to
thank our friends in Malaysia who introduced us to raptors in South-East
Asia: Ooi Beng Yean, Chiu Sein Chiong, Cheang Kum Seng, Lim Aun Tiah,
Lim Kim Chye and the late Laurence Poh.
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