Hooded Warbler
Ecoregional Scale Conservation Planning

Made possible through a partnership with the National Wetlands Research Center

Yellow-breasted Chat (Icteria virens)
The yellow-breasted chat is a Neotropical migrant that breeds in early successional habitats across the eastern United States. The species is patchily distributed in the West. Yellow-breasted chat numbers have responded to the loss of early successional habitat and have declined sharply across the northern edge of its distribution (Sauer and others 2005). Within the CH, where the species is a PIF Tier 1 priority, yellow-breasted chat numbers have fallen ~2 percent per year during the last 40 years Table 005 (Table 005) . Conversely, at the southern limit of their range, yellow-breasted chat numbers have increased (e.g., 1.3 percent annual increases in the WGCP, 1966–2005; Table 001 Table 001) .
Relative abundance of Yellow-breasted Chat, derived from Breeding Bird Survey data, 1994 - 2003.
image courtesy of www.whatbird.com

Natural History:

The yellow-breasted chat breeds in low, dense deciduous and evergreen vegetation within forests lacking a closed canopy (Eckerle and Thompson 2001). Habitat associations include forest edges and openings, regenerating forest, powerline right-of-ways, fencerows, upland thickets, abandoned farms, and shrubby areas along streams, swamps, and ponds. Chats are most abundant in 6–9 year old cottonwood plantations in the Mississippi Alluvial Valley (Twedt and others 1999). However, Annand and Thompson (1997) observed similar numbers across stands subject to alternative forest management prescriptions. In east Texas, yellow-breasted chat density is positively correlated with foliage density at 0–3 m, the percentage of saplings that are pine, and the number of shrub species. Yellow-breasted chat densities are negatively affected by increasing vegetation height, percent canopy cover, foliage density at 12–15 m, and pole tree density (Conner and others 1983).

Nest sites in Missouri are in large early successional patches >20 m from an edge and characterized by high small stem densities (Burhans and Thompson 1999). Nest success increases with patch size. Territories range from 0.5–1.6 ha.

Model Description:

The habitat suitability model for yellow-breasted chat contains six parameters:

  • landform
  • landcover
  • successional age class
  • edge, forest patch size
  • small (<2.5 cm d.b.h.) stem density

The first suitability function combines landform, landcover, and successional age class into a single matrix (SI1) that defines unique combinations of these classes Table 157 (Table 157) . We directly assigned habitat suitability scores to these combinations based on data from Hamel (1992). However, we assumed shrub-seedling habitats were optimal (suitability index score = 1.000) and pole stands were non-habitat (suitability index score = 0.000). Further, we ignored landform effects in assessing habitat suitability for this species.

Chats prefer to nest >20 m from the edge of mature forest (SI2; Woodward and others 2001). Thus, we used a 3 × 3 window to identify suitable early successional forest sites immediately adjacent to either pole or sawtimber successional age class forest. We reduced the suitability of these sites by half (i.e., habitat suitability score = 0.500; Table 158 Table 158) .

Although an early successional species, the yellow-breasted chat is associated with large patches of young forest (SI3). We aggregated all grass-forb, shrub-seedling, and sapling successional age class sites to calculate patch sizes for this species. We fit a logarithmic function Figure 092 (Figure 092) to data from Rodewald and Vitz (2005) on the relative abundance of yellow-breasted chats in early successional patches of various sizes to quantify the patch size-habitat suitability relationship Table 159 (Table 159) .

Yellow-breasted chats invariably occupy sites with high small stem densities (SI4). Therefore, we fit a logistic function Figure 093 (Figure 093) to data from Annand and Thompson (1997) relating relative yellow-breasted chat density to small stem densities Table 160 (Table 160) to predict the effect of this habitat characteristic on habitat suitability.

To calculate the overall suitability index score for yellow-breasted chats, we determined the geometric mean of the suitability index scores for forest structure attributes (SI1 and SI4) and the suitability index score for landscape composition (SI2 and SI3) separately and then the geometric mean of these values together.

Overall SI = ((SI1 * SI4)0.500* (SI2 * SI3)0.500)0.500