Hi Ryu, coincidentally there's an interpretive picture at the corresponding J'bra bird hide (sorry I forget its name) that explains the behaviour as 'anting', in that the bird allows ants to crawl over it and remove ticks, mites etc. A curious behaviour and a first for me. Cheers, Roy.
Yes, 'anting'. A behaviour exhibited by many bird species. I certainly recall seeing it indulged in by Australian Magpies, Pied Currawongs, Australian Ravens, chickens/hens, Magpie-larks, Blackbirds and Red Wattlebirds.