In this study, we evaluated the effect of forest shape on forest birds by comparing highly irregulurly shaped and more-or-less continuous forest in a plantation-dominant landscape in Japan. Although the edge effect may be weak inforests surrounded by plantations, the irregulur shape may make foraging of birds less efficient. We monitored the birds in both the breeding and migratory seasons, since recent studies have suggested that habitat use of forest birds in aforest mosaic with strong anthropogenic activities differs between seasons (Keller and Yahner 2007; Keller et al. 2009; YAmaura et al. 2009; Naoe et al.2011; but see Murgui 2007). We also evaluated whether the response of the birds differed depending on bird traits (bird migratory class and body weight), since many studies have demonstrated that the response of forest birds to vegetation changes differ with their traits (e.g.,Keller et al.2009).