Abstract
The vegetation of breeding sites of streaked shearwaters was studied to determine the effect of the birds' burrow-nesting on the vegetation of Biro Island in Kochi Prefecture, southwestern Japan. The vegetation changes along an altitudinal gradient on Biro Island, in the order of : wind-exposed grassland (e.g. Carex oahuensis var. robusta-Miscanthus condensatus community), wind-exposed evergreen scrub (e.g. Camellia japonica community, Eurya emarginata community and Ardisia sieboldii community) and evergreen broad-leaved forest (Arisaemato ringentis-Perseetum thunbergii). Burrow-nests were often found under the roots of C. oahuensis var. robusta and M. condensatus on the grassland and near the stems and roots of trees in the forest. There were no significant differences in burrow density among the three areas of vegetation. Compared with insular vegetation dominated by C. oahuensis var. robusta or M. condensatus, mean species per stand tended to be low on Biro Island. The conspicuous growth of C. oahuensis var. robusta and M. condensatus appeared to lead to poverty of plant species on the grassland. This study also suggests that the evergreen broad-leaved forest has provided the streaked shearwater on Biro Island with a stable habitat at present, although the burrow-nesting is causing some modifications in the species composition.
