There are three ways to differentiate between male and female canaries: genital inspection, color appearance and early song. Breeder Sebastian Vallelunga considers inspecting a sexually mature canary to be a virtually foolproof method, the male having a pseudo-penis that protrudes from his vent, while a female has a round dome protruding above the vent. Females ready to breed have an even, torpedo-shaped belly that narrows at one end.
The most obvious and reliable indication of gender is whether or not the canary lays an egg. Some breeders prefer to separate the sexes early to promote better song development among the males, even before the chicks fledge. Examining the early song and analyzing based on color are helpful tools.
The early song of the canary, known as the sub-song, is a dreamy trill during which the male's throat inflates, reflecting later adult behavior. During the next song-learning phase, plastic song, the male begins to integrate adult passages and phrases into his song, making it a more reliable indicator of gender.
Color appearance is a less consistent method with variations across species that apply better to canaries that are closely related or belong to the same strain. Generally speaking, Vallelunga believes that the paler canary is female.