Eastern Towhee - Preferred Habitat

Preferred Habitat

Eastern towhees range from near sea level to as high as 6,500 ft (1,980 m) along the border of Tennessee and North Carolina during the summer. A literature review reports eastern towhees up to 3,000 feet (900 m) in New Hampshire.

Eastern towhees spend the majority of their time near the ground. For instance, in Pennsylvania in spring, observations of eastern towhees below 3 feet (1 m) from the ground occurred significantly (p<0.05) more than expected based on random spatial distribution, and observations above 3 feet (1 m) occurred significantly (p<0.05) less than would be expected. In a Louisiana bottomland forest 62% of eastern towhee observations were within 2 feet (0.6 m) of the ground, and only 4% were observed above 25 feet (7.6 m). In the spring this changed, with detections of eastern towhees below 25 feet (7.6 m) declining from 70% to 65% and detections in the canopy (>25 ft (>7.6 m)) increasing from 4% to 7%.

Eastern towhees occur in many habitats, from tallgrass prairies and marshes to mature forests. However, eastern towhees are most common in early successional stands, habitat edges, and areas with similar vegetation structure throughout eastern forests.

In most communities eastern towhees are more abundant in young successional stands. Several studies found increased eastern towhee abundance on early successional sites compared to later-successional sites. Mean number of breeding eastern towhees (0.70 bird/50-m radius) and nest success rate (58%) were higher in a 15-year-old clearcut in West Virginia, than in other treatments, including a stand of yellow-poplar (Liriodendron tulipifera), black cherry, red maple, sugar maple (Acer saccharum), and white ash (Fraxinus americana) that was not harvested. In a southern Missouri oak-hickory forest, eastern towhees were not present before clearcutting or in the nearby uncut forest after cutting, but occurred at a mean density of 9.3 birds/10 ha in a 3-year-old clearcut. A study of stands of varying ages in central New York found that eastern towhee density peaked in early successional stands.

Although eastern towhees generally prefer young successional sites, variation between habitat types and years has been observed. Krementz and Powell found higher relative abundance of eastern towhee in young (2–6 years old) stands of loblolly and longleaf pine than mature (32–98 years old) stands when investigated in 1995. However, in stands compared in 1996, the 95% confidence intervals of eastern towhee relative abundance on the 2 sites had a substantial degree of overlap. The degree to which eastern towhee responds to succession is influenced by habitat. For example, in Pennsylvania there was a significant (p<0.05) difference between eastern towhee densities (number/10 ha) between mature mixed-oak forest and stands that had been clearcut about 5 years previously. However, eastern towhee densities did not differ significantly between a 1-year old mixed aspen (Populus tremuloides, P. grandidentata) clearcut, a 5-year old aspen clearcut, and a mature aspen stand. Eastern towhee abundance has been shown to peak at different times in different habitats. For instance, although in central hardwood forests eastern towhees were most abundant in regenerating stands, in loblolly and shortleaf pine forest they were most common in pole timber and mature stands. In addition, Bell and Whitmore concluded that early successional is likely too broad of a term for describing optimal towhee habitat, since high density of small trees was negatively associated with eastern towhee density in the eastern panhandle of West Virginia.

Eastern towhees seem to prefer sites with characteristics generally associated with early successional vegetation, such as low canopy cover and dense understory. Negative correlations between eastern towhee abundance and various measurements of overstory density have been found in several studies. Average density of eastern towhees across 6 habitat types in Pennsylvania was significantly (p<0.05) negatively correlated with density of overstory trees and basal area of overstory trees. Number of eastern towhees in a western Virginia hardwood forest was also significantly (p<0.05) inversely correlated with total percent canopy cover. In a loblolly pine forest in South Carolina, the average number of eastern towhee breeding territories per experimental unit was significantly (p≤0.008) negatively correlated with mid-story (10–46 feet (3–14 m)) pine (Pinus spp.) and deciduous volume.

Many studies have demonstrated a positive correlation between eastern towhee abundance and understory density. In a loblolly pine forest in South Carolina, understory (0–10 ft (0–3 m)) pine volume was significantly (p<0.001) positively correlated with the average number of eastern towhee territories per experimental unit. Yahner found the average density of eastern towhees over 6 habitat types was significantly (p<0.05) positively correlated with density of short (2–5 foot (0.5–1.5 m)) shrubs. In east-central Florida slash pine (P. elliottii) flatwoods with understories dominated by myrtle oak (Q. myrtifolia) and sand live oak (Q. geminata) and in scrub sites with scattered slash pine and cabbage palmetto (Sabal palmetto), eastern towhee densities were significantly (p=0.01) negatively correlated with mean shrub height.

Eastern towhees may associate with and avoid certain plants. In riparian vegetation in Iowa, eastern towhee density was significantly (p≤0.01) positively associated with total plant and vine species richness and negatively correlated with forb and deciduous tree species richness. In West Virginia, eastern towhees were associated with plant species that occurred on drier ridgetops, such as blackberry (p<0.02), black cherry (p<0.002), and black locust (p<0.04). These sites tended to have open canopies and low tree density. Eastern towhee density was negatively associated with plants of the moister parts of this study area, such as black tupelo (Nyssa sylvatica, p<0.006), red maple (p<0.001), and witch hazel (p<0.03). In central New Jersey eastern towhees were significantly (p=0.03) more abundant in gray dogwood (Cornus racemosa) shrubland than either eastern redcedar (Juniperus virginiana) or multiflora rose (Rosa multiflora) shrublands.

Nesting habitat: Eastern towhees typically nest on or near the ground. Several literature reviews note the predominance of eastern towhee nests below 5 feet (1.5 m). In a study of cowbird parasitism on Sanibel Island, all 5 eastern towhee nests located were within 6 feet (2 m) of the ground. Nests as high as 18 feet (5.5 m) have been reported in literature reviews. Nests higher off the ground in mixed aspen stands of varying ages in Pennsylvania had significantly (p<0.001) lower nest success. Of 13 unsuccessful eastern towhee nests, 11 were greater than 1 foot (0.5 m) above the ground.

In West Virginia, there were no significant (p>0.05) differences in habitat surrounding successful and unsuccessful nests. Large snags (≥9 inches diameter at breast height (≥22.9 cm)) did not have an effect on nesting success. Nesting success was not significantly (p>0.05) affected by stand age or distance to edge in even-aged mixed-aspen stands in Pennsylvania.

Eastern towhees nest in a variety of species including grape and blueberry (Vaccinium spp.). The majority of nests observed in South Carolina loblolly and longleaf pine forests and clearcuts were located in grape, tree sparkleberry (V. arboreum), and oak (Quercus spp.). On an oak-hickory site in West Virginia, 27% of 41 eastern towhee nests were found in grape, 17% in blackberry (Rubus spp.), 12% in greenbrier (Smilax spp.), and 12% in mountain-laurel (Kalmia latifolia). Nests also occurred in Virginia creeper (Parthenocissus quinquefolia), spice bush (Lindera benzoin), and azalea (Rhododendron spp.). In a power line right-of-way in Pennsylvania, the 6 eastern towhee nests observed occurred in Allegheny blackberry, witch-hazel (Hamamelis virginiana), blueberry (Vaccinium spp.), white oak (Q. alba), eastern hayscented fern (Dennstaedtia punctilobula) and sweetfern (Comptonia peregrina) combined, and on ground level. According to literature reviews, eastern towhee nests located on the ground are embedded in litter in dry areas and typically occur at the base of grasses, forbs, low shrubs, or small trees.

Foraging habitat: Selection of forging habitat by eastern towhees has been investigated in Massachusetts and New Jersey. When gleaning in a southeastern Massachusetts pitch pine barren, eastern towhees preferred species such as pitch pine, bear oak (Q. ilicifolia), and other deciduous trees, mainly oaks. Ericaceous species were avoided. Use differed significantly (p<0.001) from availability. On 2 New Jersey sites, eastern towhee foraging preference switched over the course of the breeding season. On a site dominated by oaks, primarily black oak (Q. velutina), eastern towhees used oaks in May, as would be expected due to their density. However, in June and July, as relative arthropod biomass declined in oaks, use of oaks was less than would be expected. On a pitch pine-dominated site, use of oaks (primarily bear oak and blackjack oak (Q. marilandica)) was greater than would be expected in May, but was proportionate to availability in June and July. These negative correlations between date and oak use were significant (p<0.025) for both sites. Use of the oak-dominated site also decreased significantly (p<0.05) through the summer.

Effects of spatial area: Eastern towhees appear to prefer edge habitats in many areas. For instance, the mean abundance of eastern towhees in a baldcypress (Taxodium distichum) in northern Florida was 18, while eastern towhees did not occur in either the baldcypress forest or the clearcut. At the interface of the baldcypress stand and a 13-year-old planted slash pine stand, mean abundance of eastern towhees was 22 breeding birds, while in the planted slash pine stand the average abundance was 15 breeding birds. Density of eastern towhees was found to decline with distance from the edge of a power line right-of-way and an oak-hickory forest in eastern Tennessee. At the edge eastern towhees occurred at a density of just over 10 pairs/40 ha, while 197 feet (60 m) from the edge eastern towhee density had dropped to 1 pair/40 ha. In addition, in experimentally clearcut Pennsylvanian forests composed of white oak, northern red oak (Q. rubra), chestnut oak (Q. prinus), scarlet oak (Q. coccinea), red maple, quaking aspen, bigtooth aspen, and pitch pine, male towhees were detected significantly (p<0.05) more often than expected in the areas where the spatial arrangement of clearcuts was most patchy.

Several studies have addressed the effect of the size of habitat patches on eastern towhees. In mixed-oak forest in New Jersey, eastern towhee frequency generally increased with patch size, although eastern towhees were detected in all plot sizes (0.5–59 acres (0.2–24 ha)) except 0.02–acre (0.01 ha) plots. On a site in South Carolina, eastern towhee frequency of occurrence increased as clearcut size increased from <2.5 acres (<1 ha) to clearcut sizes from 21 to about 32 acres (8.5–12.8 ha). On another site eastern towhee frequency declined as clearcut size increased from 19 to 33 acres (7.6–13.2 ha) to 48 to 62 acres (19.5–25.2 ha). Eastern towhees only bred in riparian vegetation patches in Iowa that were at least 650 feet (200 m) wide. In southern and eastern Pennsylvania eastern towhee nest success was not significantly (p≥0.10) different on sites with gradual edges and those with more distinct edges between "wildlife habitat openings" and oak-hickory forest.