Locomotion and Self-Maintenance
The Northern Cardinal exhibits varied locomotion, including hopping on the ground and in vegetation, as well as undulating flight in open areas. Foraging often involves short flights between branches. During courtship, males perform a distinct “Song-Flight Display” with rapid wingbeats while descending slowly.
In terms of self-maintenance, Northern Cardinals bathe year-round and engage in preening while perched. They also exhibit “anting” behavior, where they rub ants on their feathers, likely for parasite control. Bills are cleaned and sharpened by wiping them on hard surfaces. Roosting occurs late in the evening, sometimes with pairs roosting in close proximity. Before roosting, loud call notes are typically emitted. Sunbathing is common in cooler months, with individuals fluffing their feathers while perched in exposed locations. Time budgets in non-breeding captive flocks indicate a significant amount of time spent perching (74%), followed by feeding (13%) and flying (5%). Data on time budgets for wild birds is limited.
Agonistic Behavior
Agonistic interactions are prevalent in Northern Cardinals and occur in various contexts, including maintaining distance within winter flocks, defending territories, and protecting nests from brood parasitism. These interactions involve displays, chases, vocalizations, displacements, and physical attacks.
Aggressive displays include a lowered crest and specific call notes. The “Head-Forward Display,” characterized by a low crest, vibrating wings, and gaping mouth, indicates a higher level of aggression and may precede lunging. Opponents may respond by departing or exhibiting submission through raised crests and upward-pointing bills. Displacement-feeding and bill-wiping are common during aggressive encounters. Physical fights, though rare, involve grappling with feet and striking with beaks, typically lasting only a few seconds. Prolonged chases between individuals are also observed.
Song plays a significant role in territorial defense. Both males and females engage in intrasexual and intersexual aggressive interactions. While intruding males often sing and move conspicuously, intruding females tend to be silent and less obvious. Territory defense involves song, postures, pursuit, and combat. Territory sizes vary, with documented ranges from 0.21 to 2.60 hectares. While active defense of territory boundaries ceases in late summer/early fall, it resumes in late winter to early spring. Established territory boundaries tend to remain consistent year after year, though changes can occur. Both sexes leave their territories to feed and bathe, sometimes traveling considerable distances.
Simulated territory or nest intrusions elicit strong responses from cardinals. Males react to intruders with song matching, over-singing, intense chipping, flights over the intruder, and physical attacks. Interestingly, testosterone levels in males do not consistently co-vary with aggression, though they can increase during aggressive interactions. Females also defend their nests aggressively against simulated intrusions, with behaviors ranging from returning to incubate to direct physical attacks. Ornamentation, particularly face mask brightness in females, has been linked to aggression levels in some populations, potentially related to nest defense against brood parasites.
Sexual Behavior
Northern Cardinals are socially monogamous but can exhibit polygyny, sometimes due to unmated females remaining on a male’s territory or a male taking over a territory after a neighbor’s disappearance. While slight female biases in sex ratios are observed, these do not consistently explain polygynous pairings.
Pair bonds can persist through winter, though “divorces” between and within seasons have been documented. Courtship involves various male displays, such as the “Lopsided Display” and “Song-Dance Display,” where the male twists his body, sings, and sways. The “Song-Flight Display” involves the male singing while descending towards the female with rapid wingbeats. Females also engage in courtship displays, including an “open wing display” and swaying movements. Male feeding of the female during courtship and incubation is common, with females sometimes adopting a begging posture.
Ornamentation plays a role in sexual selection. Studies have focused on plumage color, crest length, bill color, and face mask characteristics. While some studies suggest redder plumage in males correlates with territory quality or reproductive success in rural areas, this relationship is less consistent in urban environments. Female preference for more colorful mates has not been definitively proven, and ornamentation does not always predict parental care behavior, such as nestling provisioning rates.
Extra-pair fertilizations (EPFs) occur in Northern Cardinals, with rates varying between populations. Mate guarding by males is observed during fertile periods, and less guarding may be associated with higher EPF rates. Females on food-supplemented territories may make more movements off their territories during fertile periods.
Intraspecific brood parasitism, where a female lays eggs in another’s nest, is rare and can vary between populations. Females exhibit nest defense behaviors against such attempts, and ornamentation may correlate with aggression levels in nest defense in some populations.
Social and Interspecific Behavior
Northern Cardinals are territorial during the breeding season and, in some populations, during the non-breeding season. Winter flocks are not strongly cohesive, and birds exhibit varying levels of tolerance towards conspecifics at feeders. Males typically dominate females and adults dominate juveniles at feeders. Flocks form after the fall molt, initially as family groups, and may enlarge by incorporating other birds. Flock membership is fluid, with individuals moving between flocks and temporarily leaving to feed.
Flocks generally consist of roughly equal numbers of males and females, with a mix of age classes. While individuals may travel considerable distances, sustained flock association is often limited. Flocks gradually disband in late winter as birds establish territories for the breeding season.
Northern Cardinals compete with other species for resources. They may give way to American Robins for nesting positions and drive smaller sparrow species away from feeding stations. They are also subject to brood parasitism by cowbirds. While generally not aggressive towards Pyrrhuloxias, male Pyrrhuloxias have shown aggressive responses to recorded cardinal songs. Interspecific nest sharing has been observed.
Occasionally, male Northern Cardinals have been observed feeding nestlings of other species. Conversely, other bird species have assisted Northern Cardinals with incubation and feeding young. Cardinal flocks may associate with various other species, such as juncos, sparrows, titmice, and goldfinches.
Predation
Adult Northern Cardinals are preyed upon by domestic cats and dogs, various birds of prey like the Cooper’s Hawk, shrikes, and mammals such as eastern gray squirrels. They are also found in the pellets of owls.
Predators of eggs and nestlings include snakes, various mammals, and other birds. Specific egg predators include milk snakes, racers, blue jays, squirrels, domestic cats, and chipmunks. Brown-headed cowbirds are known to remove cardinal eggs. Nestlings and fledglings can be taken by chipmunks, snakes, and raccoons. Video monitoring of nests has identified a wide array of predators, with Brown-headed Cowbirds being the most frequent in some studies.
Northern Cardinals exhibit anti-predator responses. Females, particularly at the egg stage, are more responsive to predator models than males, emitting chip calls and approaching the threat. Both parents show similar responses at the nestling stage. Ornamentation does not appear to be a factor in nest defense against predators. Cardinals in urban habitats show greater tolerance to humans and shorter flight initiation distances compared to those in rural areas. They react to interspecific predator alarm calls but may show reduced anti-predator behavior in noisy urban environments. Presence of predators can influence foraging behavior and territorial singing.
