1969 年 5 巻 6 号 p. 640-658_4
In 1969, a pair of Jungle Crow Corvus levaillatii japonensis bred, as in the previous year, in a ginko tree about 70m from the author's home in central Tokyo. They were kept under observation from incubation period through fledging and later periods. In this paper, their post-fledging family behavior is reported.
1. There were two periods for the chicks from their nest-leaving to territory-leaving. These are:
a. Nest-site roost period The chicks first left the nest on 24 May, only climbing up to higher branches where they sat still for the day and roosted there during a few days. Later they moved and flew around the nest-tree and roosted in trees below it. This period lasted 19 days.
b. Communal roost period One chick remained in the parents' territory and flew to communal flock roost accompanied by parents. In the morning, it returned to the territory usually later than parents, and were fed chiefly by the female, although it could forage by itself. Later, its return to the territory became irregular. This period lasted as long as 75 days. It is to be noted that this young, apparently male, left the nest (probably hatched) one day later than the other two nest-mates which showed faster growth and did not have this period, since they never came back (possibly not by accident) to the territory after they were first led to the communal flock roost by the parents one day earlier!
Probably, the problems of maturity, individuality or companionship (whether solitary or with nest-mate) may be involved in this difference.
3. During the nestling period, the parents used to fly away to communal flock roost in the evening, but in the first night of nest-site roost period (the first day of chicks' nest-leaving), the parents remained to roost under the nest-tree (to guard the young), the male and female perched some 15m apart. But, afterwards, it was usually the case that the parents did so when the young did not settle in the roost (being still hungry) towards the evening, but flew off to the communal roost when the young roosted early and quietly (having been well fed during the day).
4. Although the above are instinctive parental reactions, some judgment (in the sense of Rensch's "averbal judgment") is certainly involved and sometimes a chain of behaviors are performed in reaction to the action of the young. The following are examples:
a. On leaving to the communal roost, the parents do not fly stright away but make one or two stops on some higher buildings to look back the movements of the young. On 4 June, they then flew away, the young having been quiet, but on 6 June, when one young was still unsettled, they came back to the nest-site and roosted with the young.
b. On 8 June, the parents and young once gathered together into the nest-site roost, but the young had apparently been not enough fed during the day and one seemed to be particularly hungry. As if to test the reaction of the young, parents flew to the usual buildings, the female to the one some 180m apart and the male 380m away. On seeing still unsettled one young, female came back to the nest-tree and the young at once reacted begging food rather strongly. Then the female flew to nearby building where she had concealed food, a rat, and began to store its meat in the throat. On this, two of the young flew to that building to beg from the female, who then flew away with the rat to the building where the male was watching. There she filled her throat with enough meat and came back to the nest-tree and fed the most hungry young. Then she flew down into the nest-site roost at once followed by the young, and on seeing this, the male also came to the nest-site roost. Now the young were content and settled quietly. This was already 18.47 p. m., 8min, before the sunset, with 900 lux.