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Harrier roosts in North Thailand

By Mick Davies and Dowroong Danlamajak.

copy right - Mick Davies.

Table of Dates 2005 - 2007.

Harrier Roosts - Arrival routes - Nong Lom

I have been prompted to write this article, earlier than I would have liked as I have not completed my studies in this area. In response to fears of destruction of this site by land drainage.

Yonok Wetlands - The combined total of the 3 roosts makes these the largest roosts in Thailand are therefore of National importance: All 3 roosts are home to Grass Owl, these are the only known roosting and breeding areas in Thailand and have only recently been discovered. It is therefore imperative that these sites are fully protected. For this reason I instigated the Yonok Wetlands Project.

We need your help to make sure this area is kept safe, Yonok is a Wetland of Nation importance to Thailand and still has pristine habitat. The wetland bogs of Chiang Saen and in particular Little England must be afforded protection before this precious habitat is lost forever. I used the name Yonok Wetlands as the area is distinct from Chiang Sean Lake (Nong Bog Kai - Non hunting Area), although I believe the area as a whole is protected.

There are no roost around Chiang Sean Lake and few birds are ever seen flying over. The approach route is from the south and birds can be observed from the south western edge of the lake, however this area is difficult to access and one will only achieve small counts.

The complex of lakes is  bordered by the two roads that run north east from Mae Chan; to the west the road runs to Chiang Sean, although the Wetland and lake in not visible from the road, however the entrance road to Nong Bog Kai (NHA) is located on the right some 6 kim before Chiang Sean. And the Head Quarters are located here, take a right turn as you approach the lake. However you will not find information regarding the Harrier roosts. If you wish to visit the roost please contact me at:

The road on the east side runs roughly north east to Chiang Klong and the roost is located due west of the Temple with a huge Buddua overlooking the seen. The roost is not really visible from any road.

History: On the evening of December 19th 2005 we were birding the south side of CSL when Dowroong noticed a couple of Pied harrier flying over, a futher 17 were seen to disappear far to the south east in the space of 10 minutes.

The following evening we watched from our crake pool site, which incidentally holds 14 white-browed Crakes, and has a good selection of wetland birds, also 2 Spotted Eagles and peregrine have been wintering in this area. That evening total of 37 Harriers were seen flying to roost in the direction of the south west.

The next day was again spent searching the area for the likely roosting site and once again we positioned ourselves in the evening, this time in the rice fields and situated near the center of the floodplain, on the NE side. We were rewarded with amazing close views of 127, mostly pied harries and more than 60 adult males passing very close to us. The roost itself was still a kilometer or more to the south and was only just visible.

The subsequent days and Xmas night were spent counting and locating an access track to the roost and more important a counting watch point. This has been difficult, Dowroong and myself have spent many an evening attempting to get an accurate count of this roost.
One might think you can stand at the roost and count them all, forget it. Birds arrive from two main directions the North and West and a few from the South and SE.
With the bulk of birds arriving so late and confused with the early arrivals all getting to say hello to each other, is amazing site to see, but very difficult to get accurate counts.

Our method is  to count on the north side and the west side on consecutive nights, we can be fairly sure that a constant number of birds arrive from both areas a the counts are off similar numbers.
The North side count is always, between 120 & 138 on 5 counts between 21st December 2005 and 14th February 2006. On the first evening we counted here when we probably got them all, subsequently the line has drifted west and I feel we have been undercounting as close to dark they are to far away to see.

I reiterated the discovery of these new roosts to Phil Round and the BCST and we were delighted to show Dr Mong and his Lanna Birding Group the roosting birds arriving on the 14th Jan 2006. We also had visist from a number of interested Thai Birders including Chaiyan Kasorndorkbua on the following Saturday. Also it was a privileged to meet with Jeffery Boswell who we were able to show the roost of Little England and Ba Mak No, in January 2007.

The west side count has been increasing, only for the reason that we have gradually found better locations to observe there arrival. I think we are probably seeing about 90% as there a are more birds to the north of this stream which is on broad front.
It would be useful to have counters on the North side counting, but for the west side you will run the risk of double counting.

Maps: The pink area points in the direction of approaching birds. The stronger color denotes that this is the main route. The orange area is to show the direction of birds that over fly roosts and moving in a south westerly direction. Yellow dots are the roosting sites. The Blue arrow indicates the progressive drift of the harrier stream over a period of 3 months. The green question mark is the rice field watch point which is at present flooded out and often impossible to access.

Comparison of maps: shows that during the period of second half of January 2007 a noticeable change in the roost has taken place and this has continued with the arrival of this autumns Harriers. If you total the counts for the january 2007 period it comes close to 400. I don't know why this has happened but it may be that the roost had got to large.

However I think that the more likely explanation is that the orange stream has continued to shift west and these Harriers have now chosen to change their roost to Ba Mak No. If this is the case it is fortunate as we can protect the Ba Mak No roost more easily than Knong Lom and I hope will also solve the difficulty of counting.

November 2007: Migration and roosts

Harrier Roost counts post migration; are as follows: Raptor migration at Chiang Saen is light, this autumn was better than usual due to heavy periods of rain. The first migrants were noted on 19th September at Yonok, when 11 Honey Buzzards and 4 Chinese Sparrow Hawk flew South.

Peak migration was observed between the 27th October and 5th November, this short period was dominated by heavy rain. The rain cleared on the 6th and since that date very few raptors have been seen. It was noticeable that Harriers were seen to be moving over Yonok on the clearance of rain on the afternoon of the 4th November. On that afternoon we toured the whole perimeter of Yonok and Little England, all the concentrations of Harriers were centered around Yonok South. The Harriers were moving South in singles and I would estimate that we saw about 20. A few individuals were also seen hunting the fields around that area.

Counts were then made at all three Harriers Roosts over the following Days in early November; Little England 14 on the 7th, Ba Mak No 48 on the 8th and 62 on the 9th, Oranges contained 129 on the 12th. Total for all 3 roost is around 200, whereas the peak counts for late October were 348.

These figures clearly demonstrate that the roosts are used as migration stop over's.

Identification; It is difficult, if not impossible to be accurate in separating the numbers of Pied’s from Eastern Marsh, much less juv’s and transitional's, as most of the birds arrive in almost darkness, so I tend to just count and asses percentages of adults. One could count the earlier arrivals, but these are mostly Marsh, the birds arriving close to dusk are dominated by pied harriers.

Crake Pool site: also has a small roost of Pied Harriers varying in numbers from 7 to 16 and is located in the same area as the Ba Mak No roost, however it is a separate roost and for a number of months I was unaware of a larger nearby roost as it was out of site and hidden by a line of trees. This site is also used a sort of pre roost by some of the Harriers of the main roost (Knong Lom ), particularly if they arrive early, they just sit about and fly around.

We had an amazing site on January 16th seeing a line of 67 Pied Harries flying over from the northwest and heading for the main roost and joining a group of 50 harriers, sky pre-roosting just east of this little roost.
Having been watching roost for many years this is a rarely witnessed. I guess that it occurs when birds arrive to early to roost, or have been disturbed from the pre-roost. Or maybe it’s some sort of friendship greeting, I never witness any antagonistic behavior, the birds just circle around gaining height similar to buzzards to I guess to several hundred feet. There are at times some playful encounters

A similar event was seen at sob ruak when Dowroong counted in 47 birds, they all sat around on the hillside and small trees, at approx 10 minutes before total dark all got up and circled high into the sky, wheeling around together and literally one by one dropped into the roost, this roost is almost completely made up of pied Harriers and a max of 2 marsh Harriers.

It is noticeable that on clear skies the birds arrive late almost all arrive in the last 20 minutes before dark, whereas on dull cloudy days, the arrival period is over one to one and a half hours.

List of roost we have found in Thailand;

14 Dec 2001 - Little England: The first roost was discovered to the south Sob Ruak in December 2001 and contained about 35 birds. Harriers were again using this site in December 2005, with a maximum count of 49. This site has been given the name of Little England.

17 12 2002 - Knong Han; Lake Kamawapi (Udon Thani): a very large and beautiful lake, and a lot of birds, so we camped there overnight . There were a few Harriers hunting the area in the afternoon and towards dusk we noticed harriers coming in  from the north. A total of 325 were counted in during a period of the last 40 minutes of daylight until absolute dark, The birds were roosting in the far distant south west area of the lake, were a large reed bed was situated.

20 Dec 2005 - Knong Lom & Ba Mak No: are the Yonok Wetlands Harrier Roosts: totals should be combined with those of little England as there is interaction between all 3 sites.

22-Jan 2007 Nong Kai (marsh close to Laos border crossing): 40 birds came into roost, this area is a likely Grass Owl site as a grass/barn owl sat close to us while we camped. From our experience and it's behavior it was probably Grass Owl. This site is also of interest for the following record published by the BCST: - Most remarkably, a flock 300 of what were thought to be Common Cranes was seen in flight in Muang District, Nong Khai, on the evening of 22 January (DD, MD).  The birds approached from the north before continuing westwards up the Mekong Valley.

Table of Dates 2005 - 2007.

I am still working on this document. I will be updating both the text and tables in the near future.

In mid december 2005 we discovered a roost route

Please do not copy or publish, without my permission. This document is the original work of Mick Davies and Dowroong Danlamajak.