Here we documented brood parasitism by the poorly studied Whistling Hawk-Cuckoo (Hierococcyx nisicolor) on the Rufous-bellied Niltava (Niltava sundara). We describe new information on egg size and incubation and nestling periods for Whistling Hawk-Cuckoo as well as a novel observation regarding cuckoo nestling and host interaction. Whistling Hawk-Cuckoo chicks displayed a vivid-colored gape when host parents were provisioning food. In addition, Whistling Hawk-Cuckoo chicks displayed bright yellow wing patches to their host parents. We observed that host parents tried to place food onto the wing-patch of the nestling instead of into its mouth. We suggest that chicks displaying such wing patches mimicking nestling gapes might be a common strategy for some brood parasite species of the genus Hierococcyx. This behavior also likely occurs in 2 other cuckoos in this genus, H. pectoralis and H. fugax. Finally, we suggest that the bright yellow uropygial gland of young nestlings might also function as an extra gape for the period when the young nestling is not capable of displaying the yellow wing patches.