Acadian Flycatcher, Empidonax virescens, nest site characteristics at the northern edge of its range

Information on breeding habitat requirements for the Acadian Flycatcher (Em pidonax virescens) is scarce but important for managing remnant woodlots fo r this species considered endangered in Ontario. In 1998, we examined nest site characteristics for 11 Acadian Flycatcher nests in southwestern Ontari o. Nests were most often placed in trees of diameter at breast height (DBH) class 7.5 cm-15 cm (n = 6, 54.5%) followed by saplings (DBH < 7.5 cm) (n = 4, 36.4%), and one nest was placed in a tree of DBH class 22.5 cm-37.5 cm (9.0%). Overstory canopy height and sub-canopy height averaged 23.0 +/- 2.3 m and 4.7 +/- 3.8 m, respectively. The majority of the nest sites had a hi gh percent canopy cover (95.0 +/- 5.0%) and a low percent ground cover (42. 7 +/- 28.0%). Percent understory vegetation cover at four height intervals were uniformly below 50% and the highest total basal area was for trees of a DBH between 22.5 cm and 37.5 cm. Maintaining canopy cover in riparian are as may be an important component in promoting Acadian Flycatcher recovery.