Effect of forest structure and connectivity on bird distribution in a riparian landscape
Kondo, Toshiaki; Nakagoshi, Nobukazu
In 1999 we investigated the effects of forest quality characteristics (forest area, vegetation diversity) and forest connectivity on the distribution of two bird groups with different biological attributes in a Japanese riparian landscape of Japan. The study area consisted of 33 small forests around two rivers, and this linear cluster of small forests connected two large forests. To evaluate the effect of forest connectivity on bird distribution, we used a habitat connectivity index (CI), which quantified the effect of the spatial configuration of the small forests on bird home range movements. Bird movements were assessed in terms of movement step lengths and the number of movement steps from the two large forests. The movement step length was defined as the limited movement distance within inhospitable landscape. Stepwise multiple regression analyses revealed that the behaviors of the two bird groups were affected differently by different small forest characteristics. They also revealed that the birds' distribution was not determined by their direct distance from the large forests, but by the connectivity along a linear cluster of small forests. That is, the two bird groups did not use the small forests as 'a stepping stone' in which to stop temporarily while moving by the shortest route between the large forests; instead, they used the linear cluster of small forests as a corridor. The linear cluster of small forests facilitated bird movement across an inhospitable landscape toward isolated habitat remnants.