Difference of Large Hawk Cuckoo and Dark Hawk Cuckoo

Adult	Large Hawk Cuckoo	Dark Hawk Cuckoo
Other name	Brain-fever Bird	Bock’s Hawk Cuckoo
Upperpart	Brown with white on bend of wing	Back and rump slaty gray Wing brown and white on bend of wing
Underpart	Belly white with brownish black bars Prominent dark streaked  on breast	Breast rufous often unstreaked or lacking of streaked. Where there is, streaking only restricted to breast. Belly white with black bar
Tail	Undertail covert white, Long tail with barred brownish gray and black with broad black terminal bar tipped white	Undertail covert white Broad gray and black bar with broad black terminal bar tipped white
Head	Crown, face and necked slaty gray Face paler in front of eye Chin black, Prominent dark streaked  on throat Iris orange to buff with eye-ring yellow lemon Bill black	Crown, face and neck slaty gray, Chin, throat unstreak. Iris orange to buff, eye ring yellow lemon Bill black above greenish below

Juvenile	Large Hawk Cuckoo	Dark Hawk Cuckoo
Upperpart	Barred rufous and brown	Brownish black
Underpart	Buffish-white with broadly streaked black on breast shape of drop like	Breast slaty brown Lower breast white with dark bar
Tail	Barred rufous and black	Undertail covert with with dark bar
Head	Gray forehead Nape pale rufous with brown streak	Slaty brown with white feather on naped. Chin slaty brown

Reference

Ben F.King & Edwards C.Dickson, 1989, A Field Guide To The Birds of South-East Asia, Collins, Grafton Street, London

Craig Robson, 2017, A Field Guide To The Birds of South-East Asia, Bloomsburry, London

Del Hoyo, J., Elliott, A & Sargatal,J eds, 1997, Handbook to Birds of The World Vol 4 Sandgrouse to Cuckoo, Lynx Edicions, Bercolona, Collins, Grafton Street, London

Susan Myers, 2009, A Field Guide To The Birds of Borneo, Talisman, Singapore

Boonsong Lekagul & Philip D.Round, 1991, A guide to the Birds of Thailand, Saha Karn Bhaet Co., Ltd Bangkok

David R Wells, 1999, Birds of The Thai Malay Peninsula,Academic Press, London UK

James A. Eaton, Bas van Balen, Nick W. Brickle & Frank E. Rheindt, 2016,  Birds of the Indonesia Archipelago Greater Sundas and Wallacea, Lynx Edicion, Bercelona

Salim Ali & S. Dillon Ripley, 1981,  Handbook of the Birds of India and Pakistan Volume 3 Stone Curlew to Owl ,Oxford University Press , London