A simple population viability analysis of Tancho (Grus japonensis) in southeastern Hokkaido, Japan

We employed population viability analysis to estimate future population trends and extinction risk of Tancho, the Japanese or red-crowned crane (Grus japonensis). The stage matrix was based on 15 years of data collected by counting the number of wintering cranes and following the survivorship of banded cranes. The accidental death rate was estimated from the number of dead or seriously injured cranes collected in the Kushiro municipal zoo. Consequently, the accidental death rate was found to increase each year at 0.072% per year during the recent 14 years and 0.132% per year during final 6 years. The carrying capacity (K) was estimated from the mean mire area within the territory of a breeding pair and the geographic information system data in southeastern Hokkaido. Accordingly, K was estimated to be 1,659 in this area. Using the stage matrix, accidental death rates and K (and 20%-lower K), the simulation was conducted under three conditions: (1) the increase of accidental death, (2) the limitation of carrying capacity, and (3) the concurrent occurrence of carrying capacity limitation and accidental death increase. As a result, the extinction probability during 100 years was zero, although the accidental death rate increased at the current rate of 0.132% per year. Therefore, by artificial feeding in winter, the Japanese population of Tancho reached the adequate level, which seems sustainable unless some catastrophic factors seriously damage the population. To raise the tolerance to catastrophic factors, we discuss the probability of their distributional expansion to western or northern Hokkaido and even to Honshu.