A habitat specialist, always found in association with pine, but can occur in mixed forests with as little as 10% pine (Morse 1989). Prefers open stands with a large canopy and little understory (Anderson and Shugart 1974) such as a savannah with many tall, mature trees (Dunn and Garrett 1997). Not often found in pine plantations due to small canopy size of young trees (Nicholson 1997).

Usually places nest in pines, occasionally other conifers (Dunn and Garrett 1997). Nests are 30- 50 feet above the ground (range 10-135 feet), built on a horizontal limb, in needles at the tip of a branch, or in a cluster of cones (Potter et al. 1980). Forages in all heights of pines; generally high, along trunk and branches, but also beneath the tree on the ground (Dunn and Garrett 1997).

NATURE SERVE GLOBAL HABITAT COMMENTS:

This species is strongly associated with presence of pine and pine-hardwood forest during the breeding and winter seasons. It is a common breeder in most pine forests of the southeastern United States and in areas with pines in southeast Canada and the northeastern United States, but usually at lower densities, less common as a breeder in white pine forest areas. In the southeast, does not occur above 900 m elevation (Hamel 1992). The highest numbers seem to occur where pure stands of pine are found; less abundant as the proportion of hardwood tree species increases. Birds are rarely found in deciduous forest, scrub, and thickets, except during migration and winter.

Breeding occurs in a wide variety of pine forest types but not in other conifer forests (e.g., spruce (PICEA spp.), fir (ABIES spp.), larch (LARIX spp.), or hemlock (TSUGA spp.). In the north-central and northeastern U.S. and Canadian provinces, breeding occur in stands of red (PINUS RESINOSA), pitch (P. RIGIDA), jack (P. BANKSIANA) and white (P. STROBUS) pines (white pine also being used in the Appalachians). In southern states, breeding and winter habitat consists of stands of shortleaf (P. ECHINATA), longleaf (P. PALUSTRIS), loblolly (P. TAEDA), Virginia (P. VIRGINIANA), and slash (P. ELLIOTTII) pines. Breeding occurs less frequently in sand (P. CLAUSA) (Stevenson and Anderson 1994) and pond pines (P. SEROTINA) (Schroeder 1985) in the southeastern U.S. All forest types used may be mixed with varying proportions of hardwood species. Nesting may occur in areas of primarily deciduous forest where small groves of pines are present.

Pine warblers adapt well to pine plantations, which are used for breeding throughout the range. In Florida, Repenning and Labisky (1985) did not record breeding pine warblers in 1-, 10-, and 24-year-old slash pine plantations, but recorded 8 birds/sq km in 40-year-old plantation forests. However, they found that the species did use 1-year-old (3 birds/sq km), 24-year-old (20 birds/sq km), and 40-year-old (86 birds/sq km) pine plantations during winter.

In winter, birds commonly forage in large mixed-species flocks in southern pine forests when numbers increase because of birds migrating from farther north. At that time, flocks may forage in forest leaf litter, or in fields and pastures, usually in the vicinity of forest edge.

Density of pine warblers is inversely related to percent of deciduous vegetation within a stand (Schroeder 1985). In a breeding habitat suitability model developed by Schroeder (1985), three main habitat variables of importance were identified: percent tree canopy closure (excluding white, sand, and pond pines), successional stage of the stand, and percent of dominant canopy pines with deciduous understory in the upper one-third layer. Thus, optimal nesting habitat is provided by pure, dense, mature pine stands (excluding pine species mentioned above) that lack a tall deciduous understory. One shortcoming of this model, however, is that pine warblers do use white pine forest types for nesting; they simply tend to be less common in those pine habitats.

Conner et al. (1983) reported that mature pine forests were favored in east Texas, with increasing abundance as the proportion of pole-size pines and vegetation height increased. Tree and shrub species diversity, and foliage density at different heights had little effect. In addition, stands of sapling-sized pines were avoided.

In eastern Tennessee, Anderson and Shugart (1974) found that pine warbler distribution is influenced by several habitat variables, the strongest of which was related to average size of understory vegetation, number of canopy trees, and average size of canopy vegetation. In this area, birds selected areas with sparse understory and a dense canopy. In Ouachita Mountains of Arkansas, Wilson et al. (1995) found significantly higher densities of pine warblers in forests with a more open midstory, lower canopy coverage, lower basal area of conifers and hardwoods, and dense ground cover of grasses, shrubs, vines, and forbs (see MGMT.REQS for additional information.)

Pine Warbler was considered a forest-interior species by Whitcomb et al. (1981). Schroeder (1985) mentions a minimum estimate of 10-15 ha of forest habitat is required to sustain a breeding population. However, Robbins (1979) estimated the minimum area to be 30 ha. Interestingly, Robbins et al. (1989) found no significant relationship between probability of occurrence and forest area for pine warblers. In a old-growth hammock in Florida, Noss (1991) recorded significantly higher numbers of pine warblers closer to edges than in the forest interior during the breeding season, and considered it an 'edge-attracted species.' However, while this species may be attracted to edge habitats in some areas, edge habitats of small forest blocks probably do not support viable populations.