analysis of records of three passage migrants in Thailand: Tiger Shrike
Lanius tigrinus, Yellow-rumped Flycatcher Ficedula zanthopygia
and Mugimaki Flycatcher F. mugimaki
By Philip D. Round
of three passage migrants in Thailand are analysed to show seasonal
and geographical differences in their distribution. While two of these,
Tiger Shrike Lanius tigrinus and Yellow-rumped Flycatcher
Ficedula zanthopygia, are early autumn migrants, the third
species, Mugimaki Flycatcher F. mugimaki, is a much later
autumn migrant and, in contrast to the other two, comprises birds
that winter in Thailand as well as passage migrant individuals that
winter beyond the country’s southern border. Disproportionately
more Mugimaki Flycatchers are recorded on spring migration than the
other two species. Definitive-plumaged males of both flycatcher species
were recorded earlier on spring and autumn migration than others (grouped
female or immature birds). Although in recent decades the numbers
of migrants reported have increased due to increased ornithological
recording, the numbers of Tiger Shrikes have not increased in proportion
to those of Yellow-rumped Flycatchers, possibly indicating a decline
In the late 1960s and early 1970s, the journal British Birds
presented a series of papers analysing the patterns of occurrence
of scarce migrant birds in the British Isles. These were eventually
compiled in book form (Sharrock 1974). The clear and straightforward
graphical analyses therein were invaluable in giving a much wider
and easily comprehensible picture of seasonal occurrence patterns,
and differing geographical distributions of the species covered, inspiring
ornithologists and providing the stimulus for future fieldwork and
data synthesis. Similarly detailed analyses for an Asian site (Hong
Kong, probably one of the most heavily watched sites anywhere on the
East Asian flyway) were provided by Chalmers (1986) and Carey et
al. (2001) who gave seasonal breakdowns of records for most migrant
Increased field observation and submission of ornithological records
for Thailand and other South-East Asian countries are now also beginning
to generate datasets large enough to examine better the distribution
and seasonality of many migrant birds. Roughly one in three of all
bird species in Thailand is at least partly migratory. Precise patterns
of occurrence differ widely among species, and in some are undeniably
complex. Thailand may be host to three or four discrete populations
of (e.g.) Black Bittern Dupetor flavicollis and Chestnut-winged
Cuckoo Clamator coromandus: passage migrants, non-breeding
winter visitors from countries to the north, summer (wetseason) breeding
visitors, and possibly some year-round residents as well (Lekagul
& Round 1991).
However, the overwhelming majority of migrant species, both landbirds
and waterbirds, are non-breeding visitors from countries to the north
that spend the Palaearctic winter in tropical South-East Asia. For
many of these Thailand marks the southern limit of their South- East
Asian winter range. Even here, however, the situation is complicated
by the country’s c.14° latitudinal span, and its range of
habitats, from seasonally dry monsoon forests to rainforest. Many
Palaearctic migrants, although common in ‘continental Thailand’
(north of c.12°N), scarcely enter the Thai-Malay Peninsula (e.g.
Siberian Rubythroat Luscinia calliope). Others, e.g. Arctic
Warbler Phylloscopus borealis and Eastern Crowned Warbler
P. coronatus, appear not to winter much north of c.14°
or 15°N, and indeed the peninsular provinces may be their major
wintering area in the country.
The present paper seeks to examine the patterns of occurrence of three
Palaearctic migrant visitors which are unusual in that they occur
chiefly as spring and autumn passage migrants: Tiger Shrike Lanius
tigrinus, Yellowrumped Flycatcher Ficedula zanthopygia
and Mugimaki Flycatcher F. mugimaki. These species are easily
identified and, though not scarce, are sufficiently noteworthy to
be recorded by amateur observers, yielding a reasonably large dataset.
The principal sources of data were records submitted by local or visiting
birdwatchers from 1980 onwards; my own sight records and mist-net
captures; published records or major compilations where dates and
localities were given (e.g. Robinson & Kloss 1921–1924,
Riley 1938, Deignan 1945, Meyer de Schauensee 1946); the small number
of specimens held in the Centre for Thai National Reference Collections,
Environment and Resources Department, Thailand Institute of Scientific
and Technological Research, Bangkok, and in the Boonsong Lekagul collection
stored in the National Science Museum, Bangkok.
Although specimens and ringing records (mainly from Laem Phak Bia,
a coastal site in the Gulf of Thailand: Round & Kongtong 2009)
distinguished among sex and age classes of the three taxa, these contributed
only a small proportion of records, most of the rest being sightrecords.
For the two flycatchers, sight-records distinguished only between
birds in definitive adult male body plumage (with black upperparts)
and ‘others’ (brown-plumaged, female/immature individuals).
While male and female Tiger Shrikes in spring differ in plumage (females
with much reduced black on forehead: Wells 2007), few field observers
distinguished between the sexes. Additionally, Tiger Shrike is unusual
in that adults have two complete moults per year (Prys-Jones 1991).
Adults undergo a post-nuptial moult on the breeding grounds into a
brown, juvenile-like plumage, so that many autumn adults are difficult
to separate reliably from juveniles. Accordingly, in this analysis
no distinction was made between sexes or age-classes in Tiger Shrike,
while the two flycatchers’ age and sex classes were given as
definitive males and ‘others’.
Records for each species were grouped by ten-day period throughout
the year in order to standardise the nationwide pattern of occurrence.
Maps were used to illustrate the geographical scatter of records,
based on the six regions first proposed by Kloss (1915) and subsequently
depicted in King et al. (1975): North (alternative name North-West),
North-East, South-East, West (South-West), Central and South (Peninsula).
Over 720 records for the three species were subjected to analysis.
Although these covered a span of years from 1896 to the present, more
than 90% of the records for each of the three species post-dated 1980
(Fig. 1). Although initially it was assumed that the overwhelming
majority of records would be from the Central Region, which includes
the city of Bangkok, where most observers are concentrated, sightings
from the Central Region only contributed 39.7% of records of the three
species combined. A major surprise was the paucity of records from
the Northern Region (only 4.4% of records of all three species), even
though this includes Chiang Mai, Thailand’s second largest city,
which supports many resident birdwatchers. The North-East, the largest
region in terms of land area, was expectedly little-watched, with
the exception of Khao Yai National Park (at the extreme south-west
of the region, and the major source of records).
1. Records of three study species according to decade.
A total of 202 records involving 324 individual birds was compiled
(Fig. 2), of which 259 were in autumn and 56 in spring. Only nine
individuals (2.8%) were from the midwinter period (November to mid-March),
indicating that this species was almost exclusively a spring and autumn
passage migrant. The earliest autumn record was 11 August and the
latest 18 October, though almost all (98.8%) occurred before 10 October
(median date 13 September: Table 1). Although the peak autumn passage
period overall was the second week of September, disproportionately
more of those after the first ten days of September were from the
South, reflecting a geographical shift in the population. The peak
period of occurrence around Bangkok and elsewhere in continental Thailand
appeared to be during the last week of August and the first week of
1. Occurrence of Tiger Shrike Lanius tigrinus,
Yellow-rumped Flycatcher Ficedula zanthopygia and Mugimaki
Flycatcher F.mugimaki on
passage in Thailand.
Figure 2. Seasonal distribution of records of Tiger
Shrike Lanius tigrinus by ten-day period.
Figure 3. Seasonal distribution of records of Yellow-rumped
Flycatcher Ficedula zanthopygia by ten-day period.
Figure 4. Seasonal distribution of records of Mugimaki
Flycatcher Ficedula mugimaki by ten-day period.
5. Distribution of records of Tiger Shrike Lanus
tigrinus by region.
6. Distribution of records of Yellow-rumped Flycatcher
Ficedula zanthopygia by region.
earliest apparent spring passage record was 12 March, although since
no others were recorded until 6 April there is a possibility that
this was an aberrant wintering bird. The latest date was 6 June, although
the peak spring passage was in the last ten days of April and the
median date was 30 April (Table 1).
For both passage seasons combined proportionately more records were
obtained from the South (46.3%) relative to the Central Region (27.9%)
than in the other two species examined (Fig. 5). Additionally, five
of the nine midwinter records of Tiger Shrikes were from the South,
suggesting the possibility that a small population may genuinely overwinter
in the provinces adjacent to the Malaysian border.
The dataset comprised 395 records of 457 individuals. This species
was similarly almost exclusively a spring and autumn passage migrant,
with only seven individuals (1.5%) recorded during the midwinter period,
from mid- November to mid-March. More than twice as many individuals
were recorded in autumn (306) than in spring (144).
Autumn passage was recorded from 1 August onwards to early November,
although 71% of all autumn records were in the last ten days of August
and the first twenty days of September, and only 20 individuals (6.5%
of autumn records) were obtained after the beginning of October (Fig.
3). Spring passage was recorded from 19 March to 9 May (Table 1),
with over three-quarters of those sighted during March being male
(Fig. 3). Most observers did not distinguish between brown-primaried
first-year males and black-primaried adult males. The median date
for spring males (10 April) was one week earlier than that for females
(17 April; Table 1).
Adult males also constituted a significantly higher proportion of
earlier-arriving birds in autumn: 42.3% of August birds were adult
males, compared with only 25.5% of September birds (?2 = 7.44; p <
0.01; Fig. 3). The median date for adult males in autumn was 4 September
compared with 10 September for other age/sex-classes combined (Table
1). Four of seven midwinter birds were black-bodied males. The winter
sample is too small to draw any firm conclusions and does not necessarily
imply that proportionately more adult males overwinter, since some
could have been first-winters that had completed their body moult.
The proportion of black body-plumaged males in spring was exactly
50%, all first-year males having by then acquired black upperparts.
Fifty percent of records of Yellow-rumped Flycatchers were from the
Central Region compared with only 21.2% from the South (Fig. 6). Records
from the South did not figure disproportionately among the few Yellow-rumped
Flycatchers recorded in midwinter, so there was no evidence of a significant
wintering population anywhere, including in the extreme southernmost
provinces, even though Yellow-rumped Flycatcher winters in Malaysia
The pattern of occurrence of Mugimaki Flycatchers differed markedly
from the other two species. It was in general less frequently
recorded: there were only 127 records of 139 individuals for
analysis. Mugimaki Flycatcher was also a much later autumn migrant.
Apart from one (atypically early) report on 22 September, all
records spanned the period 2 October to 30 April. There was
a consistent and more frequent midwinter presence: 47 individuals
(33.8%) were from the period 1 November to 8 March. Relatively
few were found in autumn, but in most cases it was not possible
to distinguish reliably between autumn passage and wintering.
The marked spring passage was considered to span the period
27 March to 30 April. Of 83 individuals throughout the month
of April, nearly half (42%) were in the middle ten days of the
month (Fig. 4). Median spring passage dates were 10 April for
adult males and 16 April for ‘brown’ birds that
included both females and firstyear males (Table 1).
The geographical spread of records also differed markedly from
the other two species, with many more (34%) from the North-East
than any other region. This compared with 26.8% from the Central
Plains and 23.6% from the Peninsula, a relatively more even
geographical spread among regions (Fig. 7). Mugimaki Flycatcher
showed a greater affinity for forest and taller trees than Yellow-rumped
Flycatcher and was not usually recorded in coastal mangrove
scrub, and other relatively open habitats where most watching
and ringing of migrant birds is undertaken. It also has a greater
affinity for upland habitats. Although most Central Region records
were at or near sea-level, the headquarters area of Khao Yai
National Park, the source of most of the North-East Thailand
records, lies at 700–800 m elevation.
Figure 7. Distribution of records of Mugimaki
Flycatcher Ficedula mugimaki by region.
All three species considered have breeding ranges in the Eastern Palaearctic,
with the smallest range being found in Tiger Shrike, breeding mainly
in Ussuriland, the Korean Peninsula, Japan and north-east China (Brazil
2009). Two of the three breed in smaller woodlots and parks (including
in urban areas: J. W. Duckworth in litt.) in addition to
forest. The third, Mugimaki Flycatcher, is the most restricted to
forest on the breeding grounds (Brazil 2009) and also tends to be
more restricted to taller woodland on passage in South-East Asia than
the other two. Although both Tiger Shrike and Yellow-rumped Flycatcher
winter commonly in Malaysia (Wells 2007), neither does so regularly
or widely in peninsular Thailand (apart from a few Tiger Shrikes that
possibly winter in the extreme southern provinces, immediately adjacent
to the Malaysian border). Mugimaki Flycatcher is a winterer and passage
migrant in both seasons in Malaysia but commonest above the montane
ecotone (Wells 2007). In Laos this species is also mainly associated
with hill-slope and montane habitats, both on passage and in winter
(Duckworth et al. 1998, J. W. Duckworth in litt.).
It is highly likely, therefore, that many more might be recorded during
winter if the little-covered southern Thai mountains were more accessible.
As passage migrants, Tiger Shrike and Yellow-rumped Flycatcher showed
overall many more records in autumn than in spring, while the reverse
was true in Mugimaki Flycatcher. The relative scarcity of both Tiger
Shrike and Yellow-rumped Flycatcher in spring is unlikely to be an
artifact of coverage as, in general, more birdwatchers and bird photographers
are searching for birds at that time than in autumn.
Some other migrant shrikes (e.g. the Western Palaearctic-breeding,
African-wintering Red-backed Shrike L. collurio and Lesser
Grey Shrike L. minor) are noted ‘loop migrants’,
and take a more easterly route on northward (spring) migration than
on southward (autumn) migration (Moreau 1961, 1972). There is no obvious
reason, however, why there should be any parallel among the Eastern
Palaearctic–South-East Asian migrant species. Additionally,
Tiger Shrike is very rare in Hong Kong, with only nine records, all
of which were in autumn (Carey et al. 2001), so it is unlikely
that spring migrants take a more easterly northwards route. Nor are
there many records to the west (see below). Because Tiger Shrike is
a relatively late spring migrant, with northwards passage extending
well into May (latest Thai-Malay Peninsula date 17 May: Wells 2007)
some may be overlooked. The most likely explanation, however, is that
most northbound spring migrants, having fattened in Malaysian or Indonesian
wintering areas, overfly Thailand (and southern China). This interpretation
is corroborated by the scarcity of records from Laos in spring, even
though coverage by visiting birdwatchers in Laos probably reaches
its annual peak at that time (J. W. Duckworth in litt.).
The depiction of differing geographical distributions among the three
species is still tentative as even now some regions (especially the
South-East) are much less-visited than others, and would surely contribute
many more records if better covered. In the case of Yellow-rumped
Flycatcher the disparity between the 50% of records from the Central
Plains region compared with only 21.2% from the South may to some
extent be due to a proportionate disparity of (especially autumn)
coverage between the two regions. However, Wells (2007) suggested
that the species was less common in the Thai peninsular provinces
in autumn than in spring, and this is borne out by the present analysis.
The apparent scarcity of Yellow-rumped Flycatcher records from the
North (which contributed just 2.8% of records for both seasons combined)
might be partly due to inadequate coverage of favoured lowland garden
or parkland habitats in that (mainly hilly or mountainous) region.
But such a pattern might also occur if Yellow-rumped Flycatcher had
a slightly more north-east/southwest migratory orientation that caused
it largely to miss the North on both migrations. North-East Thailand
contributed 15.3% of spring records, while Yellow-rumped Flycatcher
is also regular in Laos in spring (J. W. Duckworth in litt.).
This would tend to rule out spring overflight as a cause for scarcity
in the North. In Tiger Shrike by comparison, overflight is a more
likely explanation as there were equivalently few spring records from
both the North and North-East.
The Yellow-rumped Flycatcher in Hong Kong has a pattern of occurrence
similar to that of Tiger Shrike. It is very scarce in spring (only
one record: Carey et al. 2001), suggesting that it either overflies
southern China or follows a route that bypasses the coast. Although
more frequent in autumn, it is still much less common there than in
Thailand. The peak passage in Hong Kong, in mid- September, more or
less corresponds with that 8º latitude further south, in Thailand’s
In autumn, Mugimaki Flycatcher was a much later migrant, with passage
peaking over one month later than the other two. This made it difficult
to distinguish between migrants and winterers. The late timing of
passage in this species is also corroborated from night-time interceptions
in Malaysia (Wells 2007). The predominance of spring passage records
almost certainly accurately reflects a genuine greater abundance then,
especially since the chances of encountering any individual passage
migrant should be lower in spring than in autumn. Not only is the
total population of any given Palaearctic migrant in spring smaller
than that in autumn, owing to winter mortality, but spring migrants
in general may also make shorter migration stop-overs, owing to the
imperative to return to the breeding grounds to take up territory.
In Hong Kong, where the Mugimaki Flycatcher is similarly a scarce
winter visitor and passage migrant, it is also recorded more commonly
in spring than in autumn (Carey et al. 2001).
In general, the broad correspondence between Thailand and Hong Kong
in records of the three species gives no reason to speculate that
autumn and spring migratory routes differ in major respects for any
of them, other than in possible spring overflight of northern South-
East Asia and southern China. Nor does any species pass much to the
west in either season. Yellow-rumped Flycatcher is a vagrant to peninsular
India, while neither Tiger Shrike nor Mugimaki Flycatcher have been
recorded there (Rasmussen & Anderton 2005). In Burma, Yellowrumped
Flycatcher and Tiger Shrike are known from the extreme east of the
country and Tenasserim only, while there are no records of Mugimaki
Flycatcher (Robson 2008).
The Mugimaki Flycatcher showed a generally more eastern distribution
in Thailand than either Tiger Shrike or Yellow-rumped Flycatcher.
Well-watched forest sites in Western Thailand, such as Kaeng Krachan
National Park, which covers a similar altitudinal range to Khao Yai,
have yielded many fewer records than the latter site, while there
were only two records from the very heavily watched mountains in Chiang
Mai Province, in the western part of the North. Definitive male Mugimaki
Flycatchers accounted for 42% of spring records, proportionately fewer
than in Yellow-rumped Flycatcher. Although this might be expected,
since male Mugimaki Flycatchers may not attain black upperparts until
their second year, the difference in the proportions of recognisable
males was not statistically significant.
Although the numbers of all three migrant species recorded increased
markedly after 1980, owing to greatly increased coverage by birdwatchers
and to better collation of records, the numbers of Tiger Shrikes recorded
did not increase in proportion to those of Yellow-rumped Flycatchers,
and indeed there were fewer Tiger Shrike records post-2000 than in
the preceding decade (Fig. 1). Given the fact that the peninsula contributed
most records of Tiger Shrike overall, one possible reason for this
disparity might be that coverage increased more in the Central Region
post-2000 than it did in the South (where either coverage, or record
submission, may have actually declined). Another possibility is that
the decline in records reflects an ongoing global decline in numbers
of Tiger Shrike that was reported by BirdLife International (2009).
This analysis shows how records collected mainly by amateur birdwatchers
may make a contribution to the scientific record in Thailand and South-East
Asia as they have long done in Europe and North America. Although
the present paper has drawn on records spanning a roughly 110-year
period, over 80% of the records of each species post-dated 1990 and
therefore provided a reasonable ‘snapshot’ of present
patterns. Studies on the phenology of breeding and migration have
assumed added urgency owing to the weight of evidence that climate
change is having major impacts on birds and biological systems (Crick
& Sparks 1999, Butler 2003, Coppack & Both 2003, Sanderson
et al. 2006). Migrant birds may be at elevated risk from
climate change because their annual cycles are adapted to cope with
the vicissitudes of climate in widely separated wintering and breeding
areas, which may differ in the extent to which they are affected by
climate change. Additionally, clearance of forest for agriculture
has impacted the status of both resident and migrant birds, removing
large swathes of habitat for inhabitants of forest, while simultaneously
opening up huge areas for those that favour open country. Wells (2007)
has documented a gradual southwards expansion of the winter range
of migratory Black Drongos Dicrurus macrocercus, an open-country
winterer, in Malaysia, and range shifts among a suite of other migrant
species might be expected.
Migrant birds additionally face a number of other threats including
direct persecution, and indirect disturbance. Mortality during nocturnal
migratory flights due to collisions and disorientation caused by communications
towers, other man-made structures, and gas flares from offshore oil-fields
has also been demonstrated and could cause population declines (Lid
1977, Morris et al. 2003). Improved understanding of migrant
bird ecology, and a capacity to monitor changes in the numbers and
distribution of migrant birds, are therefore of great importance.
Although this paper establishes a rough baseline on seasonality and
distribution for the three species considered, more intensive and
systematic monitoring, from a greater and more even spread of sites,
for a greater range of species, and comparing seasonal patterns decade
by decade, or by five-year period, into the future would refine and
improve understanding. This could be done through better collation
of records from local birdwatching groups (several of which already
exist for the Thai regions), university bird clubs, and possibly in
future even formally established bird observatories, including those
in neighbouring countries. Round & Kongtong (2009) recommended
the establishment of a bird observatory at one coastal site, the Laem
Phak Bia Environmental Research and Development Project, Phetchaburi,
where ringing has already been implemented for a decade, and which
contributed a number of records to the present analysis.
I am grateful to the many birdwatchers and bird photographers who
contributed their sightings to this analysis. I should also like to
thank Des Allen, Robert DeCandido, Will Duckworth, David Pearson,
Andrew Pierce, Stephen Rumsey and David Wells for their comments on
drafts of this paper. I am grateful to the staff and director of the
Laem Phak Bia Environmental Research and Development Project for permission
to ring birds there. I thank the directors of the Thailand Institute
of Scientific and Technological Research and the National Science
Museum, Thailand, for permitting access to specimens. I also thank
Niti Sukumal and Supatcharee Tanasarnpaiboon for kindly preparing
the distribution maps. My work is supported by The Wetland Trust (UK).
BirdLife International (2009) Species factsheet: Lanius tigrinus.
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Philip D. Round, Assistant Professor and Regional Representative,
The Wetland Trust, Department of Biology, Faculty of Science, Mahidol
University, Rama 6 Road, Bangkok 10400, Thailand. Email: email@example.com