of Black Drongo Dicrurus macrocercus in southern Thailand
in autumn 2003
By Robert DeCandido,
Chukiat Nualsri and Deborah Allen
This article was originally published in Forktail 20 (2004) the journal
of the Oriental
Bird Club (OBC) and was kindly submitted by Robert
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The Black Drongo Dicrurus macrocercus is a
mediumsized passerine of temperate and tropical Asia. It breeds
in south-east Iran, Afghanistan, India, south-east Tibet, and from
northern China discontinuously south through south-west Thailand,
to Bali and Java. Northern populations migrate, wintering at lower
altitudes and latitudes, reaching as far south as central India
in the west, and Malaysia and Sumatra in the east, where they occur
in tropical savanna, grassland and agricultural areas (Jeyarajasingham
and Pearson 1999).
Little has been published about Black Drongo migration. Historically, the species
was considered an ‘extremely abundant’ migrant in September
at Beidaihe, China, occurring in ‘huge noisy parties’
(La Touche 1920). In an autumn migration survey of the same area
from 1986–1990,Williams (2000) counted a maximum of 452 in
1986, but only 196 in 1990. Melville and Fletcher (1982) counted
1,444 flying west in less than two hours of observation on 14 October
1980 near Bangkok, Thailand. Numbers migrating through, and wintering
in, Thailand appear to have declined in recent years (P. Round verbally
2003, D. Wells in litt. 2004).
As part of a study of raptor migration through southern Thailand in autumn 2003
(DeCandido et al. 2004), we also counted the number of migrant Black
Drongos passing the watch site.
Chumphon (10o28’N 99o13’E; sea level) is a town on the
coastal plain of southern Thailand.The north-south Bilauktaung range
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). The study site (10o28.40’N
99o13.26’E) was in a freshwater marsh at Ban UTapao, Tha Yang
subdistrict, 4.6 km east-north-east of Chumphon, and approximately
2 km north-east of the coastal highway. The vegetation comprises primarily sedges Carex
spp., rushes Juncus spp. and cat-tails Typha spp.
with lone, scattered trees. In clear weather, 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 location of our watch site was approximately
435 km to the south-south-west of the one used by Melville and Fletcher
were counted using 10x binoculars by RDC, assisted at times by CN
and DA. Count protocols followed those described in Bildstein and
Zalles (1995) for raptors.We scanned primarily north for approaching
migrants. A bird was counted if it passed across an imaginary east-west
line at the watch site. Observations typically began at 07h00 local
time and usually ended at or before 17h00.Weather conditions (wind
speed, barometric pressure, temperature, humidity) were measured
hourly throughout the day with a hand-held ‘weather station’,
the Kestrel 4000 (Nielsen-Kellerman Corporation, USA). Wind direction
was assessed with a compass.We counted migrants during late September
to early November because this period corresponded to the peak of
the diurnal bird migration observed in previous years by CN.
During 378 hours of observation between 27 September and 9 November
2003, we counted 11,290 migrating Black Drongos (29.9 birds/hour).
Drongos migrated throughout the day, primarily between 07h45 and
17h45 (Fig. 1). Between dawn and c.07h30, Black Drongos made short
flights from overnight roosts to foraging areas. Most birds began
migrating soon after,along with bee-eaters Merops spp.
and swallows Hirundiniae, but before the onset of most
raptor migration. The daily peak of migration was at 08h00–10h00,
when 28% (3,129) of all individuals were counted (37.2 birds/hour).
Numbers fell by early afternoon, but increased again in the late
afternoon. There was often a large movement at 17h00–18h00,
presumably of birds heading to roost. We rarely saw drongos migrating
after 18h00. In contrast, Crowbilled Drongo Dicrurus annectans was frequently mist-netted at
night in autumn 1965–1973 at Fraser’s Hill, Malaysia
(Medway and Wells 1976, McClure 1998, D.Wells in litt. 2004).
Migration peaked in late October, with 2,089 birds (97.1 birds/hour) on 17–18
October following two days of heavy rains throughout much of Thailand,
and 2,766 birds (55.3 birds/hour) on 26–30 October (Fig. 2).
By early November, there were fewer migrating drongos, and we assumed
that many of those we saw had settled on their winter territories.
Further north at Beidaihe, Williams (2000) estimated that drongo
migration peaked on 6–17 September. Our highest single hourly
count (618) on 17 October was similar to the 825 birds/hour seen
in the late afternoon of 14 October 1980 by Melville and Fletcher
There was no significant difference between the number of Black Drongos
counted when winds were from the north to north-west compared to the
east or south (P²=0.13, P<0.05). The vast majority of migrant
drongos passed the watch site at a height of <35 m, and usually
<8 m. Early in the season, drongos occurred as singles, but formed
loose flocks from 5 October onwards. Often, 5–20 birds would
pass the watch site, sometimes across a 30 m front. The species did
not appear to be an obligate flocking species (sensu Kerlinger
1989) like, for example, the Blue-tailed Bee-eater Merops philippinus.
1 : Daily pattern of Black Drongo migration (totals seen
per hour) at Chumphon, Thailand in autumn 2003.
Figure 2 : Seasonal pattern of Black Drongo migration
(totals seen per day) at Chumphon, Thailand in autumn 2003.
We sincerely appreciate the encouragement and thoughtful advice of
Phil Round of Mahidol University. Uthai Treesucon of Bangkok provided
helpful ideas and suggestions to the migratory bird monitoring team.We
also appreciate the kindness shown to us by our colleagues of the
Malaysian Nature Society including Cheang Kum Seng, Liew Siew Lan
and Ooi Beng Yean, Audrey and Laurence Poh, Regina Anthony and Chiu
Sein Chong. Martin Williams called to our attention his work with
migratory birds at Beidaihe, China. William Duckworth read a version
of this manuscript and provided many erudite suggestions for improvement.
Desmond Allen provided GIS coordinates of the watch site. Jevgeni
Shergalin alerted the authors to obscure information about the Black
Drongo in Asia. We thank David Wells for information derived from
his many years of field work and research on the birds of the Thai-Malay
peninsula for access to his unpublished information. This research
was supported by grants from the Bobolink Foundation and the Oriental
Bird Club, plus a Hawk Mountain Project Soar Award.
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Mountain Sanctuary, 1700 Hawk Mountain Road, Kempton, Pennsylvania
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Correspondence: 1831 Fowler Avenue,The Bronx, New York 10462-3708,
U.S.A. Email: email@example.com
Nualsri,Thayang Administrative Organization, 135-1 Kromluang Chumphon
Road, A. Muang Chumphon
86000,Thailand. Email: firstname.lastname@example.org
Allen,The Linnaean Society of New York, P.O. Box 1452, Peter Stuyvesant
Station, New York 10009, U. S A.