This small warbler is often hard to see as it forages in dense foliage of the treetops. However, it is easy to hear; the male seems to repeat his buzzy trickle-up song constantly from early spring through mid-summer at least. Northern Parulas hide their nests inside hanging Spanish moss in the South, or in the similar Usnea lichens in the North, where they are impossible to spot except by the actions of the parent birds.
Mostly insects. Feeds on small beetles, flies, moths, caterpillars, egg clusters, true bugs, ants, bees, wasps, and other insects, also spiders. Also eats some small berries. May feed nestlings many soft green larvae.
Pairs often return to same nesting site year after year. Males sing during migration and throughout nesting season, even when feeding young. Nest: Placed usually in a hollow excavated in hanging tree lichens (Usnea) or Spanish moss, 4-50' above the ground. When no lichens or Spanish moss available, also constructed of dangling clumps of twigs or pine needles, or placed in rubbish left by floods in branches hanging over stream. Nest is small hanging pouch of lichen and twigs, unlined or lined sparsely with soft shreds of moss, grass, pine needles, and hair. Built solely by female, but male accompanies her on trips to the nest.