The Acrocephalus Issue

When talking about Little Brown Jobs or those small birds that are difficult to identify, most birders in Thailand would immediately think of the Phylloscopus warblers because there are so many species of them. They’re definitely one of the birders’ ultimate nightmares. But for me, I’d say there are something even more frightening than identify the Phyllocs, the Acrocephalus warblers!


Oriental Reed Warbler is the commonest and most widespread Acros in Thailand.


Mostly seen foraging along scrubs and grassy area near water.



Frequents perching in the open to dry itself up in the morning. Note pale tip to tail feathers.


Can be rather showy and perch on grass top for a look out or to sing before spring migration


Note long and pointy primary projection


Often shows hint of greyish streaking on breast (more prominent in spring)

There are 8 species of Acrocephalus warblers, or generally called “reed warblers”, in Thailand. They can be divided into 2 main groups, the large and the small reed warblers. Only 2 species are considered as large reed warblers; the Oriental Reed Warbler and the Clamorous Reed Warbler. These two are approximately 20 cm in length or about the size of a bulbul. The latter is an extremely rare vagrant OR a highly overlooked species in Thailand with very few accepted records, while the former is the commonest and most widespread reed warbler in the country. The identification of these two species is extremely challenging (definitely more challenging than what it seems in the guide books!). I still haven’t been able to scrutinize all the large reed warblers that I’ve seen, so I assume that all of them are Oriental Reed Warbler for the meantime.


Among the small reed warblers, the Black-browed Reed Warbler is the commonest species.


It’s about the same size and at times can resemble a Phylloscopus warbler like Dusky Warbler or Radde’s Warbler.


Most of the time, the black eyebrow is thick and obvious enough to separate it from other similar species.


But other times, the black eyebrow can appear faint and thin.


But that might depend on the angle!


Or the angle plus lighting

What about the other 6 species of reed warblers in Thailand? They’re all small-sized reed warblers which are approximately about the same size as a sparrow, or just a little larger than most Phyllocs. The commonest and most widespread species among these small reed warblers is the Black-browed Reed Warbler.

With a prominent black eyebrow over the pale supercilium, you might think that it’s quite straightforward to identify this species. Most of the time, it is indeed, but every once in a while, you’ll come across odd individuals that look like it might be a different species.


Manchurian Reed Warbler is listed as Vulnerable by the IUCN Red List. I photographed this bird in my local patch in Mae Taeng, Chiang Mai on 18 September 2004. It is still by far the only record of this species in the north.



Note completely pale tip to lower mandible (mostly blackish in Black-browed RW). For Manchurian RW, this can turn blackish only in spring and summer.


Structurally, it is more similar to Paddyfield Warbler (which was once treated as the same species) than Black-browed RW. The tone of plumage is also warmer and more rufous-tinged like Paddyfield Warbler rather than Black-browed RW as well.

The species that is most often confused with Black-browed RW is the globally threatened Manchurian Reed Warbler. It is a  range-restricted breeder in China that winters in South-East Asia. In Thailand, it is reported to be a passage migrant in the north and central part of the country and spend winter along the eastern coast of southern Thailand. Recently, it was also found to be wintering in Malaysia and Cambodia too.

When compared to Black-browed RW, the Manchurian RW generally shows a different structure by having longer tail and longer bill. The lower mandible also lacks dark tip unlike in Black-browed RW which shows dark tip to lower mandible throughout winter. In Manchurian RW, the dark tip is only developed in spring and summer. The plumage is also warmer and more rufous-tinged similar to Paddyfield Warbler, which it was once treated as the same species. The black eyebrow is often faint and thin and the pale supercilium tend to be thinner and more pointy at rear end than in Black-browed RW.

Note: be aware that some Black-browed RW can also show faint/thin black eyebrow too! Better photos and more identification notes on Manchurian/Black-browed RW can be read from Dave Bakewell’s post here.


Paddyfield Warbler is a rare winter visitor to small areas of northern Thailand.


This adult bird was ringed at Nam Kham Nature Reserve in February 2014 and was found to be a regular visitor at the Rubythroat Hide in 2016.



Bill is rather short and shows prominent dark tip to lower mandible throughout winter.


Plumage is warm rufescent-brown with rather short primary projection

Things get even more confusing with the small reed warblers that lack black eyebrow. Let’s start with the Paddyfield Warbler, a bird that is quite widespread in Europe and Asia but is a rare winter visitor in Thailand. The Manchurian Reed Warbler was once treated as a subspecies of Paddyfield Warbler and it’s no surprise. They share many similar characteristics like warm rufescent-brown plumage and very similar wing formula and length of primary projection. The Paddyfield Warbler can often show a hint of dark eyebrow over the pale supercilium as well, but never as black as in Manchurian/Black-browed RW. However, unlike in Manchurian RW, the Paddyfield Warbler always shows dark tip to lower mandible throughout the winter. The bill is also shorter and more pointy at tip than in Manchurian RW. In Thailand, it can only be found in several locations in northern part of the country including Nam Kham Nature Reserve in Chiang Rai where these photos were taken.


Blunt-winged Warbler is one of the trickiest birds to see and even trickier to identify!


It’s one the small reed warblers that lack any trace of dark eyebrow, which makes it look rather plain-faced.


I probably wouldn’t be able to identify this bird without this lucky, even though blurry shot that shows the wing formula.



Note the long P1 that extends beyond primary coverts


Structurally, it’s a small Acros with long tail.


Supercilium is short and not as prominent as in Paddyfield Warbler.

But the most challenging group of all reed warblers, or probably all LBJs, is the plain-faced small Acros! There are 3 species recorded in Thailand; the Blunt-winged Warbler, Blyth’s Reed Warbler and Large-billed Reed Warbler. All three species share some very similar characteristics including the lack of dark eyebrow, long bill and shortish supercilium which is not so prominent making them look rather plain-faced.

The commonest and most widespread species among the 3 is the Blunt-winged Warbler which is a winter visitor to wetlands throughout northern and central Thailand. Despite its abundance, it’s never easy to see one because it’s a very shy and skittish bird. Even though you finally get to see it, the bigger challenge would be to identify it!

It’s almost impossible to identify these small plain-faced reed warblers without seeing the wing formula.


Left: Blyth’s Reed Warbler; Right: Blunt-winged Warbler


Left: Blunt-winged Warbler; Right: Blyth’s Reed Warbler. Note the short and blunt primary projection as suggested by the name in Blunt-winged Warbler.


The long P1 which extends beyond the primary coverts is another main ID feature for Blunt-winged Warbler.


Blyth’s Reed Warbler is a rare winter visitor in Thailand. Note the much shorter P1 and shorter tail than in Blunt-winged Warbler.


Primary projection is much longer and more pointed than in Blunt-winged Warbler.


Blyth’s Reed Wabler (left) tends to have colder brown and often grey-tinged plumage than in Blunt-winged Warbler (right). The supercilium is also more obscured in Blyth’s RW.


Blunt-winged Warbler in profile; note rather warm brownish plumage and short but distinct supercilium.


Blyth’s Reed Warbler in profile; note cold greyish-brown plumage and less prominent supercilium


When seen in the field, the Blyth’s Reed Warbler is generally a long-billed and short-tailed bird.

The Blyth’s Reed Warbler is a rare winter visitor that has only been recorded several times from 2 locations in Thailand; i.e. Nam Kham Nature Reserve in Chiang Rai and Bung Boraphet in Nakhon Sawan. Compared to the Blunt-winged Warbler, it has colder and overall more greyish-brown tone to the plumage with much longer primary projection and shorter tail. Its P1 is also shorter and doesn’t markedly extend beyond primary coverts like in Blunt-winged Warbler. Behaviour-wise, the Blyth’s RW prefers dryer areas with scrubs or forest edge near wetlands, while Blunt-winged Warbler is a strictly wetland bird that can only be found in reed beds.

Finally, the most challenging identification among all reed warblers (and LBJs, in my opinion) is between the Blyth’s and Large-billed RW. The Large-billed Reed Warbler is an extremely rare and very little known species which has only been recently rediscovered in 2006 by Philip Round at Laem Phak Bia in Phetchaburi and followed by another record from Nam Kham Nature Reserve in 2008. Basically, the Large-billed RW has longer bill and warmer tone to the plumage, but these two can overlap in almost every morphological aspect. There was even one bird at Nam Kham Nature Reserve that we weren’t able to identify even after measuring it in hand, so DNA test was required! In the end, the DNA result revealed that it was a Blyth’s Reed Warbler. I’m not going to touch on how to identify these two, so here’s a photo of a true Large-billed Reed Warbler from Nam Kham Nature Reserve instead.


The second record of Large-billed Reed Warbler in Thailand from Nam Kham Nature Reserve. Photo by Woraphot Bunkhwamdi.


Pak Pli: 23 May 2015

I’ve heard of Pak Pli fields in Nakhon Nayok for so long, but haven’t got the chance to visit the place until 23 May 2015. The area holds one of the biggest roost for Black Kites in Thailand including both the migratory lineatus and the nationally endangered govinda races. The place also serves as winter ground for the scarce Rosy Pipit and Thailand’s first Greater Short-toed Lark was also recorded here in 2013.


One of the abundant Oriental Skylarks performing its song flight over the colourful grassland


Asian Golden Weavers were nesting along the small irrigation canal. Here’s a brightly coloured male.



Female lacks the bright golden plumage, but is still a pretty smart bird.

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Male Cinnamon Bittern trying to blend into the surroundings.


Another pair of Cinnamon Bitterns; male on top and female bottom


Soaring male Red Turtle Dove


Bronze-winged Jacanas were quite common along the roadside canals, but proved to be difficult to get good shots of.


I left Bangkok very early in the morning and arrived at the area around 7AM. It was a very birdy morning. Songbirds were singing from literally every direction, particularly the larks. Oriental Skylark was the most abundant species, followed by Indochinese Bush Lark and Horsfield’s Bush Lark being the least abundant. The road leading into the field was aligned by a small irrigation canal which was filled with Asian Golden Weavers‘ nests. They could be photographed extremely easily just from the car.


A pair of Bronze-winged Jacanas; note how small the male (bottom) is compared to the larger female


White-breasted Waterhen was also seen foraging along the canal.


A pair of Lesser Whistling Ducks


Adult Black Kite race M. m. govinda, a rare resident in Thailand


Note the lack of large whitish patch on base of primaries and yellow cere and feet


Another adult govinda Black Kite perching on a Eucalyptus tree.


A flying over Oriental Darter

The dirt road that goes around a large area of grassland, rice fields and Eucalyptus plantation is also aligned by small canals with lush Lepironia grass. Many birds were seen along the canals including many Bronze-winged Jacanas, White-breasted Waterhens, Plain Prinias, Zitting Cisticolas, Javan Pond Herons, Lesser Whislting Ducks and Cinnamon Bitterns.

Several Black Kites were seen perching and patrolling over the fields. They were all M. m. govinda which is a resident and nationally endangered bird in Thailand. Pak Pli is most likely the largest stronghold of this declining taxon. In winter, they come to roost altogether along with the migratory M. m. lineatus of which some authors split as Black-eared Kite. According to the Thai Raptor Group, 1,998 lineatus and 101 govinda Black Kites were counted at this roost on 22 November 2014.


Striated Grassbird was one of the commonest birds and one of the most vocal.


Striated Grassbird proudly performing its loud melodious song in flight



It’s much harder to spot them while foraging through thick grass.


I was glad to come across a lone Long-tailed Shrike race longicaudatus, another endangered bird of the central plains.


Paddyfield Pipit with nesting materials


The least abundant lark in the area, Horsfield’s Bush Lark


Great (or White-vented) Mynas like to follow buffalo herds and prey on insects that are disturbed by the animals.



Little Cormorants were seen easily along the road.


I was really surprised to come across this male Watercock moulting into breeding plumage standing in the open completely unaware of my presence.

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It stood motionlessly for a while, probably undecided about what to do nest, before slowly walked further into the open field and across the road into a small canal on the other side.


Then it behaved like a normal Watercock i.e. always hiding in thick vegetation.

At one point, I felt like there should Watercocks since the habitat looked so good for this species which is one of my favourite birds. Suddenly, I actually came across an unbelievably showy male Watercock standing motionlessly on the open ditch next to the road. It didn’t flush as the car approached but stood still for a moment before walking into a canal on the other side. I have no idea why it was behaving like that since it is normally an extremely shy bird. But as it went into the canal, it began to act more like a normal Watercock and didn’t show up again.


Many Oriental Skylarks were feeding in the newly ploughed fields.

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Most of the birds were in worn plumage.



When birds were quiet, Asian Golden Weavers were always there for me.



Female at the active nest


Oriental Pratincoles were also abundant but difficult to approach.


Juvenile following and begging for food from its parent

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But it was sad to see rows of mist nets over a large fish pond. Many birds were trapped in the nets and they weren’t even fish eaters; for example, this poor Oriental Pratincole.


On the other hand, this fish-eating Whiskered Tern seemed to be well aware of the nets and successfully avoided them. There were some 6-7 of these terns flying around over the pond. They’re probably over-summering in Thailand.


Striated Grassbird singing against the drizzling rain


Intermediate Egret against the many coloured grassland


One of several Oriental Skylarks that decided to forage on the road



There were many lotuses in the canals. Here’s the sweet coloured Sacred Lotus.