Pairs may mate for successive years, but some also ‘divorce’ between seasons or choose a new mate when one dies. Pairs generally stay together year-round but are not necessarily monogamous. DNA studies of two methods of cardinals found that between 9 and 35% of nestlings weren’t fathered by the female’s mate. Mated pairs sometimes sing together before nesting. 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. If the mating is successful, this mate-feeding may continue throughout the period of incubation.
Males sometimes bring nest material to the female, who does most of the building. She crushes twigs with her beak until they are pliable, then turns in the nest to bend the twigs around her body and push them into a cup shape with her feet. The cup has four layers: coarse twigs (and sometimes bits of trash) covered in a leafy mat, then lined with grapevine bark and finally grasses, stems, rootlets, and pine needles.
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