Ecological and life-history traits related to range contractions among breeding birds in Japan

Extinction risk is not evenly distributed among all species. Therefore, identifying shared characteristics of species that have shown serious population declines and range contractions can help to predict which types of species are likely to be vulnerable to extinction. The present study investigates ecological and life-history traits related to range contractions among breeding birds in Japan. Recent changes in nationwide distribution of each species were estimated using data from distributional surveys of breeding area in Japanese birds (1978 and 1998–2002). The Phylogenetic generalised least squares model revealed that the species with the following five traits have experienced particularly severe range contractions: medium body size, low annual productivity, solitary breeding, occurrence on farmland, and long-distance migration. Earlier theoretical studies have revealed that species with medium body sizes and low annual productivities are vulnerable to habitat loss and fragmentation. Thus, results from the present study, which showed a decline in species with those two traits, may be indicating that habitat loss and fragmentation play an important role in range contractions in Japanese birds too. Whether, and through which mechanisms, coloniality reduces extinction risks of populations remains to be investigated. A large number of studies, mainly in Europe, have revealed the mechanisms behind the declines in farmland birds and long-distance migrants. In Japan, however, few studies have explored the processes through which such species decline. Direct causes of population declines in species sharing traits associated with range contractions need to be investigated urgently so that appropriate conservation measures can be taken.