Pre-roosting behavior of the harrier, all age-classes of pied harriers came to land on ground 1-2 kilometers away from its night-roosting site on tall-grass wetlands, for approximately a half an hour to rest and preen itself, then just before dusk they launched the "flight-over-roosting site" phenomenon until the night falls and drop down to the "roosting pit" for each individuals. The roosting pit is formed by the harriers place itself upon the grass stems to make oval-shaped depression. It is unknown, as of now, if the same harrier individual uses its own roosting pit repeatedly. However, on surveys at the roosting site, the roosting pits apparently were used several times through winter, as new and old pellet were observed in the pits. The roosting pits are aggregated in one particular area amongst tall Swamp Rice Grass หญ้าไซ /Leersia hexandra/, and distance between pits are 30 to 300 cm.

.. Observations at two night-roosting sites of Eastern marsh, Pied, Western and Hen Harriers of c.400 birds in Chiang Rai by C. Kasorndorkbua & C. Wongchai.

More information on night roosting of harriers in Harrier E-News 3
http://thairaptorgroup.com/TRG/modules.php?name=publication