Cerulean Warbler Habitat
The Cerulean Warbler breeds in large blocks of mature upland and lowland hardwood forests (Hamel 2000) and, in Wisconsin, occurs most often in oak-hickory and maple forest types (Mossman 2006). It is considered to be area-sensitive, but appears to possess a degree of plasticity in its habitat affinities (Jones et al. 2001). Habitat measures such as extent of canopy, tree species composition, stand age, and tract size vary considerably across its range (Hamel 2000). However, large tracts, large deciduous trees, and structural complexity in the canopy appear to be important habitat characteristics (Mossman and Hoffman 1989, Jones and Robertson 2001, Wood et al. 2006). Wood et al. (2006) also found higher Cerulean Warbler abundance in areas with high snag density, which likely contributed to the structural complexity of the canopy.
This species seems to show some resiliency to certain forms of forest disturbance (Jones and Robertson 2001). Cerulean Warbler abundance was similar in unharvested periphery stands adjacent to clearcut and two-age harvests compared to unharvested control stands, suggesting that small harvests within a mature forest do not negatively impact Cerulean Warbler abundance in the remaining forest, only within the clearcut harvests themselves (Wood et al. 2005). However, it should be noted that the impacts of timber harvest can vary depending on the surrounding landscape, i.e., agricultural versus forested.
Cerulean Warbler populations are concentrated in the southern region of Wisconsin, although even here they breed sparingly (Mossman 2006). This species expanded its range northward in the mid-twentieth century but remains a rare summer resident in the north (Robbins 1991). Forest fragmentation and development pressures have reduced the amount of suitable habitat available for this species within the state (WDNR 2005). The few remaining areas that support Cerulean Warblers occur along the larger rivers, floodplains, and upland forest blocks in the Kettle Moraine, Baraboo Hills, and around the tension zone.