"An active bird of the mid- and upper tree canopy, where it gleans for insects and spiders, the Northern Parula (“little titmouse”) seems to prefer riparian vegetation. In the northern part of its breeding range, it is found in moist deciduous, coniferous, or mixed woodlands where it builds its nest in beard moss (Usnea lichen). Southern populations nest in the pendulous Spanish moss (Tillandsia) which is abundant in hardwood bottomlands along rivers and swamps. Other nesting sites and materials are used where neither lichen nor moss are found."

http://bna.birds.cornell.edu/bna/species/215/articles/introduction