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.
The habitat suitability model for yellow-breasted chat contains six parameters:
- 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
. 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;
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
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
Yellow-breasted chats invariably occupy sites with high small stem densities (SI4). Therefore, we fit a logistic function
to data from Annand and Thompson (1997) relating relative yellow-breasted chat density to small stem densities
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