Cardinals, also called "redbirds," do not migrate and have traditionally been more common in warmer climes such as the U.S. southeast. However, in recent decades they have expanded their common range north through the United States and even into Canada. This population growth may be due to an increase in winter birdfeeders and to the bird's ability to adapt to parks and suburban human habitats. Only males sport the brilliant red plumage for which their species is known. The color is a key to mating success—the brighter the better. Females are an attractive tan/gray.
Cardinals are active songbirds and sing a variety of different melodies. Males can be aggressive when defending their territory, and they frequently attack other males who intrude. This tendency sometimes leads cardinals to fly into glass windows, when they charge an "intruding bird" that is really their own reflection.
Cardinals are fairly social and join in flocks that may even include birds of other species. During mating season, however, groups dissolve into pairs. Male birds feed their monogamous partners as they incubate clutches of eggs—typically three per season.