The orchard oriole breeds in wooded riparian zones, floodplains, marshes, and shorelines (Scharf and Kren 1996) but also occur in open shrublands and low-density human-dominated areas (e.g., farms and parklands). Orchard orioles are semi-colonial in optimal habitat but are relatively solitary in marginal areas. This species is a common brown-headed cowbird host.
The orchard oriole habitat suitability model contains five parameters:
- successional age class
- forest within a 1-km radius
- basal area
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 orchard oriole vegetation and successional age class associations in Hamel (1992). However, we adjusted Hamel’s values to account for the preference of orchard orioles for mesic habitats (e.g., riparian zones, floodplains, and marshes; Scharf and Kren 1996).
Orchard orioles are not area-sensitive but are generally restricted to forested landscapes. Therefore, we included only local forest composition (SI2) in our model to discount forest patches that were isolated within a matrix of non-forest landcover. Conversely, the species is an edge species whose abundance declines in heavily forested regions (Scharf and Kren 1996). Therefore, we assumed landscapes with 70–80 percent forest provided optimal habitat suitability (1.000) and reduced suitability symmetrically as landscape composition shifted from these optima
Orchard orioles are most abundant in areas with scattered trees. Therefore, we modeled the basal area (SI3)–habitat suitability relationship as a quadratic function
that maximized suitability index scores at intermediate basal area values
To calculate the overall suitability index score, we determined the geometric mean of SI scores for forest structure indices (SI1 and SI3) and then determined the geometric mean of this value and landscape composition (SI2).
Overall SI = ((SI1 * SI3)0.500 * SI2)0.500