Factors Affecting Breeding-Site Selection of Northern Goshawks at Two Spatial Scales in Urbanized Areas

Environmental Factors Affecting the Reproductive Rate of Urban Northern Goshawks

“…We determined that a plot of 11.3-m radius was an appropriate size because our previous surveys of these forests showed that the vegetation structure (tree size, number of understory trees and shrubs, etc.) in the area up to this distance from the nests clearly differed from other places in the same forest (see Natsukawa et al 2017).…”

“…Furthermore, trees that may hinder the flight of goshawks are also increasing in potential nest stands. Goshawks in urban areas prefer nest stands in forest environments that do not hinder flight, rather than areas of high canopy coverage (Natsukawa et al 2017). In the current study, some goshawks used nesting environments where the canopy coverage was low, even though these areas were associated with lower reproductive rates.…”

“…However, the forests in urbanized areas tend to be fragmented, and NND has greater variability. Goshawks inhabiting the study area select breeding sites where there is both forest and open space (Natsukawa et al 2017), and NND can be as low as approximately 700 m in such sites. Urbanization of the study area is increasing, and forest and open areas each make up approximately 10% of the study area (see Methods).…”

“…We plotted a circle of radius 2 km, approximately the size of a goshawk home range in Japan (Kudo et al 2005), around each nest and determined the percentage of land-cover types in each. Goshawks inhabiting the surveyed area tended to forage along forest edges (Natsukawa et al 2017). Therefore, we measured the tangent length of forest and open area, and the tangent length of forest and vegetated built-up land.…”

“…However, goshawks have expanded their range to urban areas in Japan and Europe and have been breeding in urban environments there (Higuchi et al 1996, Rutz et al 2006b). Urban goshawks' feeding habits (Würfels 1994, 1995, Altenkamp 2002, Rutz 2003, Rutz et al 2006a, home ranges and space use (Rutz 2006), foraging strategies (Rutz 2012b), breeding-site selection (Natsukawa et al 2017), reproductive parameters (Solonen 2008, Rutz 2012a, 2012b, and colonization history (Rutz 2008) have been investigated, but studies on the determinants of their reproductive rate are limited. Here, we report the results of an investigation of the reproductive rate of a Northern Goshawk population in an urbanized area from 2014 to 2016, in which we examine the relationship between the number of fledglings and environmental factors such as nesting and foraging environments, anthropogenic disturbance, predation risk, and intraspecific competition.…”