The eastern wood-pewee is a familiar species of woodlands throughout eastern North America (McCarty 1996). All woodland types (deciduous, mixed, and evergreen) are utilized by eastern wood-pewees; however, the species consistently selects open park-like conditions on xeric sites with limited canopy cover and low shrub densities (Robbins and others 1989, McCarty 1996). Eastern wood-pewees are positively associated with increasing sawtimber tree density, reaching a threshold at 100 trees/ha, when a negative relationship develops (Best and Stauffer 1986 cited in McCarty 1996; Robbins and others 1989).
Eastern wood-pewees are common in both forest interiors and edges, are generally area-insensitive, and may occupy fragments as small as 0.3 ha (Blake and Karr 1987, Robbins and others 1989). Their cryptic nests placed high in the canopy may limit predation and parasitism, allowing pewees to occupy small fragments without the adverse effects on reproduction common to other open cup nesters (McCarty 1996, Knutson and others 2004, Underwood and others 2004). Eastern wood-pewees do not occur in riparian corridors with <24 percent forest cover in the landscape (Perkins and others 2003b).
The eastern wood-pewee habitat suitability model contains five parameters:
- successional age class
- percent forest in a 1-km radius
- sawtimber (>27.5 cm d.b.h.) tree density
The first suitability function combines landform, landcover, and successional age class into a single matrix (SI1) defining unique combinations of these classes
. We directly assigned suitability index scores to these combinations based on vegetation type and successional age class associations of eastern wood-pewees reported by Hamel (1992).
Eastern wood-pewees can occupy extremely small fragments but may require a minimum amount of forest in the landscape. Therefore, our model did not include a patch size function and instead relied solely on landscape composition (SI2). We used a logistic function
to predict habitat suitability index scores from the percent forest in the landscape
We included sawtimber tree density in the habitat suitability model and used the 100 trees/ha threshold observed by Best and Stauffer (1986) as the optimal value in a quadratic function
linking sawtimber tree density (SI3) to eastern wood-pewee habitat suitability. We assumed a symmetrical decline in habitat quality as sawtimber tree density increased or decreased from this optimum
To calculate the overall suitability index score, we determined the geometric mean of individual suitability index functions relating to forest structure (SI1 and SI3) and then calculated the geometric mean of this value and landscape composition (SI2).
Overall SI = ((SI1 * SI3)0.500 * SI2)0.500