This is an adult male. Usually males are solid blue, but here in East Asia, the distinctive race M.s.
philippensis has chestnut underparts. Formerly classified with the true thrushes, the rock-thrushes have been
moved to the Muscicapidae (Old-world Flycatchers and Chats) family. Canon PowerShot SX60. References:
Clement, P. & Hathway, R. (2000) Thrushes. Princeton Univ. Press, Princeton.
Collar, N. (2019). Blue Rock-thrush (Monticola solitarius). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/58415 on 26 March 2019).