Habitat
Inhabits forest and swamp edges, regenerating clearcuts, open-canopied forests (including deciduous, pine [PINUS], pine-hardwood and spruce-fir [PICEA-ABIES]; particularly those with a well-developed understory), reclaimed strip mines, mid-late successional fields, riparian thickets, overgrown fencerows, shrub/small-tree thickets, and other brushy habitats. Nest is typically constructed on the ground, concealed among dense, woody vegetation. Later nests (renests, second broods) are more likely to be built above the ground (usually to 1.5 m, but up to 5.5 m) than earlier nests (Palmer-Ball 1996, Greenlaw 1996). However, regional differences in nest placement occur. Even early nests are more likely to be above ground in the Southeast than in the Northeast (J. Greenlaw, pers. comm.). Habitat selection does not differ appreciably between the breeding and non-breeding seasons (Greenlaw 1996). Significantly more abundant in open-canopied deciduous forest having relatively dense understory growth than in closed-canopied forest with relatively sparse understory vegetation (Annand and Thompson 1997, Chadwick et al. 1986, Childers et al. 1986, Crawford et al. 1981, DeGraaf et al. 1991, Robinson and Robinson 1999, Yahner 1993).
Ecology
DENSITY: In Massachusetts, density of breeding birds varied from an average of 1.78 individuals/ha in closed-canopy forest stands to an average of 7.41 individuals/ha in selectively-harvested stands (Chadwick et al. 1986). In Pennsylvania, the mean number of breeding individuals ranged from 0.17-0.99/ha in six forest types (Yahner 1986). In Arkansas, the number of territorial males ranged from 0.025-0.23/ha. Lowest densities occurred in a burned field and a dry forest, whereas the highest density occurred along a forest edge (James and Neal 1986). In the Pine barrens of southeastern Massachusetts, breeding bird density ranged from about 1.5-3/ha during a three-year period (Morimoto and Wasserman 1991). In New Jersey, population density varied from 0.5 males/ha in mesic oak forest to 0.8 males/ha in xeric pine-oak woodland (Greenlaw 1996). Territory size can vary inversely with experimentally altered food supplies. However, territories appear to contain more than the minimal food stocks necessary for maintenance and reproduction (Wasserman 1983).
INTRA- AND INTERSPECIFIC AGGREGATIONS: Forms loose flocks during the winter, ranging in size from 8-27 (mean = 17) individuals. These wintering groups often form mixed-species foraging flocks with Dark-eyed Juncos (JUNCO HYEMALIS), White-throated Sparrows (ZONOTRICHIA ALBICOLLIS), Field Sparrows (SPIZELLA PUSILLA), Song Sparrows (MELOSPIZA MELODIA), Northern Cardinals (CARDINALIS CARDINALIS), Tufted Titmice (BAEOLOPHUS BICOLOR), Winter Wrens (TROGLODYTES TROGLODYTES) and Carolina Chickadees (POECILE CAROLINENSIS; Barbour 1941).
SITE FIDELITY: Exhibits breeding site fidelity. In New Jersey, one male returned to the same 24-hectare section of oak forest in 5 of 6 years (Greenlaw 1996). In another New Jersey study, the return rate was 20% the first year after banding and 43% thereafter (Leck et al. 1988).
POPULATION PARAMETERS: Sex ratio data are limited; however, sex ratios determined to date are male-biased (at least temporarily) or no different from parity (Greenlaw 1996). Estimated annual probability of survival among adults is 0.58 (Savidge and Davis 1974 cited in Greenlaw 1996). Oldest known individual was at least 12 years, 3 months old (Terres 1991).
PARASITES: Host to at least 14 species of ectoparasites and six internal parasites (Greenlaw 1996).
Reproduction
Both sexes become sexually mature in second year of life (Greenlaw 1996).
PHENOLOGY: Breeding season varies with latitude. In the southeastern U.S. (Florida and Georgia) nest building and oviposition begin in late March-early April, whereas in New England these activities are delayed until mid-May (Greenlaw 1996, Stevenson and Anderson 1994). In the Midwest, breeding activities begin in mid- to late April (Mumford and Keller 1984).
OVIPOSITION/INCUBATION: Dates of oviposition can vary among habitats at the same latitude. In New Jersey, for example, oviposition began earlier in mesic oak forest than in xeric pine barrens. This difference was attributed to earlier foliage development and the concomitant earlier appearance of additional invertebrates in the oak forest (Greenlaw 1978). Egg-laying generally terminates by mid- to late July, but can extend into mid to late August. Clutch size is 2-6 (usually 3-4 eggs), and incubation begins with the laying of the penultimate or ultimate egg (Greenlaw 1996). Clutch size can vary at the same latitude, with larger clutches being produced in habitats with greater food supplies (Greenlaw 1978). Incubation, by the female only, lasts 12-13 days. Both sexes feed the nestlings and fledglings.
FLEDGING: Young leave the nest when 10-11 days old. Produce 1-2 broods per season; will also renest after nest failure (Greenlaw 1996).
NEST SUCCESS: At two sites in New Jersey, egg success (number of eggs that produced fledged young) varied from 28.3-35.6%. Nest predation rates ranged from 31-73% at these two sites (Greenlaw 1996). In West Virginia, nest success (nests that fledged at least one young) was 36.5% (Bell and Whitmore 1997).