Species: Setophaga ruticilla

BREEDING POPULATION DENSITY: Published information on bird densities from breeding bird censuses in the southeastern U.S. between 1947 and 1979 were summarized by Hamel et al. (1982). Mean (standard error) density was listed as 8.7 (2.8) pairs per 40 ha with a density range of 2.7-87 pairs per 40 ha. In northern New Hampshire (White Mountains), Sabo (1980) recorded average densities of 40 pairs per sq km in subalpine habitats, and 9 pairs per sq km in virgin spruce groves. Sherry and Holmes (1988) reported a range of 2.5-6.75 male territories on 10-ha sites at the Hubbard Brook Experimental Forest, New Hampshire. When population trends for the month of June (mid-breeding period) at Hubbard Brook were analyzed for the period 1969-1986, Holmes and Sherry (1988) found the mean (standard deviation) number of adult to be 28.67 (8.84) birds per 10 ha. In Maryland, Whitcomb et al. (1981) reported territorial densities to be 71 males per sq km. <br><br>Two studies of bottomland hardwood forests provide data from similar censusing techniques: Mitchell and Lancia (1990) found densities to be the highest in edge habitat (an average 0.14 birds per 25 m radius 10-min point count) in South Carolina. On the Roanoke River National Wildlife Refuge in North Carolina, R. Sallabanks (unpubl. data) found densities to be highest in the interior of wide levee forest patches (an average 0.57 birds per unlimited radius 10-min point count). Between 1986 and 1988, Sherry and Holmes (1989) found the number of yearling males to be low (0-1 males per 5 ha) compared with older males (6-8 males per 5 ha). <br><br>WINTERING POPULATIONS: Solitary in winter (Stiles and Skutch 1989). Defends winter territory (Jamaica, Holmes et al. 1989, Marra et al. 1993; Mexico, Rappole and Warner 1980); individuals commonly return to the same territory in successive years. Density in winter in Jamaica was 10-51 per 10 ha, comparable to breeding densities reported for eastern U.S., but greater than densities reported for other sites in the Caribbean and Mexico (0-17 per 10 ha) (Holmes et al. 1989; see also Bennett 1980). Winter densities were listed by Hamel et al. (1982) as a mean (standard error) of 2.5 (1.5) pairs per 40 ha with a density range of 1-4 pairs per 40 ha. <br><br>TERRITORY SIZE: Little information exists on territory size. Freemark and Merriam (1986) listed territory size as less than 2 ha near Ottawa, Canada. Based upon 14 birds, Sabo (1980) found territory size to be 0.6 ha. <br><br>COMPETITION: Several studies have addressed habitat selection and territory occupancy in response to both intra- and inter-specific competition (Ficken and Ficken 1967, Sherry 1979, Sherry and Holmes 1988, 1989, Secunda and Sherry 1991). In New Hampshire, Sherry and Holmes (1988) found the density of redstart territories to be slightly higher when a dominant competitor, the least flycatcher (EMPIDONAX MINIMUS), was absent (approximately 4.4 territories per 4 ha) than when present (approximately 4.0 territories per 4 ha). Least flycatchers locally excluded after second year redstarts from best patches of habitat within a heterogeneous array of such patches (Sherry and Holmes 1988). <br><br>MORTALITY FACTORS: Weather accounted for most nest losses during the building stage and caused starvation of nestlings in some years at Hubbard Brook (Sherry and Holmes 1994). Widespread starvation in 1984 was probably caused by a series of heavy rainstorms during the nestling period that depressed insect abundances, or reduced foraging time or success, or both (Sherry and Holmes 1992).