Bionomics and Sociology of Tancho, Grus japonensis

Abstract

Territoriality of Tancho or the Japanese Crane, Grus japonensis was studied in Kushiro marshlands from March 1971 to June 1972. Two types of social patterns are recognized: The permanent territorial pattern and the segregation of breeding and wintering areas. The difference of these two social patterns seems to be correlated with availability of winter food supply. Daily life of a pair is confined within a territory. The territory involves three important places for: nesting, roosting and feeding. The daily home range markedly varies, in the period of early parental care, its minimum size being as small as 1/1600 of the largest one. But the territory remains almost constant through breeding season. The alternation of guarding chick and searching food may be most responsible for the reduction of daily home range. To raise their chicks in huge open and bioeconomically poor marshlands, the reduction of daily home range is advantageous for Tancho. The territory occupants exhibit territorial defense at the invasion of alien birds. The sequence of invasion and defense varies considerably according to age of invaders, season, time and weather conditions. Duetting decreases the chance of invasion and increases the withdrawal of invaders. Social units found in Tancho in the breeding seasons are classified as territorial pairs, families, non-territorial two associated yearlings, solitary yearlings and solitary adults.