Cold, winter months often give way to large winter flocks of cardinals, which travel close to home in groups of 70, or more, and live within a close proximity to each other. Cardinals are probably most well-known for the whistling. Pairs of birds can often be seen spitting out loud, clear whistling noises year round. It is not uncommon for females to counter sing with a male, whistling a duet of sorts. Some variations in song, such as accent, have been noted in cardinals living in different regions.
Cardinals survive on a diet made up mostly of insects.
Because of this, cardinals are often introduced into areas in North America to help control insect populations. Cardinals also eat seeds, wild fruit, leaf buds, berries and flowers. Almost one-third of the cardinal's summer diet consists of insects, and 90 percent of its winter diet is made up of vegetable matter. Cardinals live in nests, which are made from small collections of twigs, pieces of bark, roots, and lined with grass. Their natural habitats include thickets, bushes, woodlands, parks, and residential areas.