The preferred seashells of C. variabilis include Babylonia, Nerita, Phasianella, Thais, Tonna and Turban seashells.
The taxonomy of the Slender-billed Cuckoo-Dove is disputed, and some authorities split it into two species: M. amboinensis (Slender-billed Cuckoo-Dove) of eastern Indonesia and Papua New Guinea, and M. phasianella (Brown Cuckoo-Dove) of eastern Australia from Weipa and Aurukun in the north to Bega in the south, and most inland at Atherton and Toowoomba.