The northern cardinal is a mid-sized perching songbird with a body length of 21–23 cm (8.3–9.1 in) and a crest on the top of the head.

Juvenile cardinals do not have the distinctive red-orange beak seen in adult birds until they are almost fully mature.

On hatching, their beaks are grayish-black and they do not become the trademark orange-red color until they acquire their final adult plumage in the fall.

It was once prized as a pet, but its sale was banned in the United States by the Migratory Bird Treaty Act of 1918.

[6][7] The term "northern" in the common name refers to its range, as it is the northernmost cardinal species known.

[6] Northern cardinals are numerous across the eastern United States from the southern half of Maine to Minnesota to the Texas-Mexico border and in Canada in the southern portions of Ontario, Quebec, New Brunswick and Nova Scotia, all the way east to Cape Breton Island.

[1] In 1929, Forbush described the species as rare, and by 1955 Griscom reported the bird to be "pushing northward" when recorded annually at feeding stations.

[10] The adult male is a brilliant crimson red color with a black face mask over the eyes, extending to the upper chest.

[11] The female is fawn-colored, with mostly grayish-brown tones and a slight reddish tint on the wings, crest, and tail feathers.

[17][18][19][20] During winter, cardinals will fluff up their down feathers in order to retain warm air next to their body.

The legs and feet are thin and lack feathers, and are vulnerable to rapid heat loss.

[13] The northern cardinal has a distinctive alarm call, a short metallic chip sound.

[5] The songs of the two sexes of the northern cardinal, although not distinguishable by the human ear, are sexually dimorphic.

[25] The diet of the adult northern cardinal consists mainly (up to 90%) of weed seeds, grains, and fruits.

[10] Other common items include corn, oats, sunflower seeds, the blossoms and bark of elm trees, and drinks of maple sap from holes made by sapsuckers.

The male sings in a loud, clear whistle from the top of a tree or another high location to defend his territory.

DNA studies of two populations of cardinals found that 9–35% of nestlings were not fathered by the female's mate.

During courtship they may also participate in a bonding behavior where the male collects food and brings it to the female, feeding her beak-to-beak.

The cup has four layers: coarse twigs (and sometimes bits of trash) covered in a leafy mat, then lined with grapevine bark (when available) and finally grasses, stems, rootlets, and pine needles (where available).

The female builds a cup nest in a well-concealed spot in dense shrub or a low tree 1–3 m (3.3–9.8 ft) off the ground.

[34] Newly hatched cardinals weigh an average of 3–3.5 grams,[5] are naked, blind, and immobile, and do not have feathers until they are 4–5 days old.

Very young nestlings will beg if the nest is moved, but as they grow older, they start to only respond to their parents' presence or their songs.

They are produced every 3 or 4 feedings, and female cardinals sometimes stimulate defecation by poking the nestling near the cloaca.

[35] It is illegal to take, kill, or possess northern cardinals, and violation of the law is punishable by a fine of up to US$15,000 and imprisonment of up to six months.

[37] A study conducted in 2016 in Atlanta, Georgia, on West Nile virus transmission in the United States found that unlike other species, northern cardinals biologically suppress the disease upon infection.