The habitat requirements of the painted bunting are poorly understood. The species is generally found in areas of scattered woody vegetation. Kopachena and Crist (2000a) characterize painted bunting habitat in northeast Texas as “wooded areas in otherwise open habitat” as opposed to indigo buntings which occur in “open areas in otherwise wooded habitat.” Painted buntings utilize smaller, more heterogeneous groups of trees than indigo buntings, but microhabitats differ little between the species (Kopachena and Crist 2000b). Painted buntings occur in narrow riparian strips in eastern Texas and their abundance decreases quickly as widths exceed 70 m (Conner and others 2004).
Nests are constructed in low, woody vegetation (Lowther and others 1999), and territory size varies with population density. In Missouri, territories ranged 0.64–6.66 ha and included 80 percent pasture and 20 percent woodland. This species is a common host of both brown-headed and bronzed cowbirds.
The habitat suitability model for the painted bunting contains six parameters:
- successional age class
- distance to edge
- interspersion of open and forested lands
- 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 suitability index scores to these combinations based on relative habitat rankings for vegetation and successional age class associations of painted buntings reported in Hamel (1992). We assigned shrub-seedling age classes higher values than Hamel (1992) based on qualitative descriptions in Lowther and others (1999).
Painted buntings are an early-successional species associated with edges. We used data on territory density from Lanyon and Thompson (1986;
to define an inverse logistic function linking suitability index scores to distance from an edge (SI2;
The presence of both forest and open landcovers in the landscape (SI3) is perhaps the most important component of painted bunting habitat. We maximized suitability index scores for painted buntings in landscapes containing 50 percent forest and 50 percent open habitats based on unpublished data from Kopachena. Norris and Elder (1982; cited in Lowther and others 1999) observed buntings in landscapes with 20–80 percent forest, and we assumed this represented the minimum amount of forest needed for painted buntings to be present
As an early successional species, the painted bunting occupies habitats containing high small stem densities (SI4). We assumed mean stem density values observed by Kopachena and Crist (6400 stems/ha; 2000b) were characteristic of average habitat suitability (suitability index score = 0.500) and optimal habitat required twice as many stems
We fit a smoothed logistic function through these data points
to quantify the relationship between small stem density and suitability index scores for painted bunting habitat.
To calculate the suitability index score for sapling and pole successional age class stands, we determined the geometric mean of SI scores for forest structure (SI1 and SI4) and landscape composition (SI2 and SI3) separately and then the geometric mean of these means together.
SISap-pole = ((SI1 * SI4)0.500 * (SI2 * SI3)0.500)0.500
We assumed shrub-seedling successional age class stands were used irrespective of edge or landscape composition. Thus, we calculated the suitability index score as the geometric mean of forest structure attributes alone (SI1 and SI4).
SIShrub = (SI1 * SI4)0.500
The overall suitability index score is the sum of the two age-class specific SIs:
Overall SI = SISap-pole + SIShrub