“The bill of the Blue Whistling-thrush (Myophonus caeruleus dicrorhynchus) has been described as variable from full black to yellow (see Wells 2007 for a full description).
“In my experience I have only ever encountered birds with a yellow-orange bill with black on the culmen-ridge from the base to the cutting edge (see the 3 images provided here).
Dato’ Dr Amar-Singh HSS
Ipoh, Perak, Malaysia
27th May 2018
Location: Ipoh, Perak, Malaysia
Habitat: Limestone outcroppings at outskirts of the city with secondary growth
Wells, D.R., 2007. The birds of the Thai-Malay Peninsular. Vol. II, Passerines. Christopher Helm, London. 800 pp.