In January, male cardinals sing from tall trees to establish their few acre territories. Cardinals will defend their territories and even mistake their own reflections for another cardinal invading their territory. If fighting against themselves occur, cover the object that the reflection is in for they may fight until they die from exhaustion. Both the male and females sing, which is unusual for birds, and will often counter sing between themselves. The cardinal is a persistent singer throughout most of the year which is unlike most birds.
Most ornithologists believe cardinals mate for like.
Mates are chosen for their breeding site but it is known that the cardinal with the best song and one that is a great looking beautiful cardinal is likely to be bonded up first. Female cardinals begin building their nests in early April with a little help from the males, usually raising two to three broods. Their nests are located between three to twenty feet about the ground in dense thickets, spruce and deciduous small trees and thick shrubbery. You will find the nests mostly in the lower ten feet. Cardinals never nest in nest boxes.