都会ハシブトガラスのなわばり繁殖観察(続2)

抄録

This third part reports the observations of family life from 31 to 34 days after hatching, 5-2 days before flying of chicks, May 19-22, 1969, of a territorial breeding pair of Jungle Crow Corvus macrorhynchos. It was confirmed that one adjacent pair had the nest in gingko tree (in American Embassy) 300m apart from the nest under observation.
1. In this later part of nestling period, the female could have occasional long free recessions of more than 30 minutes off the nest for her own exercise (by chance also food taking), flying to peripheral buildings within the territory far from the nest, whence she advertised herself with 'ka, ka' notes to her mate who stayed on duty while her absence watching around the nest tree on high top of building or a tree, and he called her back if she was late to return. Although the male's long absense from nest site is for food search for the family, the female's long recessions are principally for her own excercise, her chief source of food being those brought and stored by the male at various places around the nest site. The time spent by male and female together increased and became more frequent to be ready for family life with fledged young.
2. During the early morning parents are active eating for themselves and feeding the chicks with stored food around the nest, each of them visiting the nest with more or less 30 minutes intervals, average 15 minutes by both sexes, but the male soon begins his food search for the day widely within his territory and his feeding intervals (to chicks) are prolonged, and those of the female are shortened. Thus, on May 19, 12.35-16.13 p. m., the female's intervals were average 19.30min., as against the male's of 78min. (also on May 20, 10.00-11.30 a. m., the average feeding intervals were 38min, in the female and 72min. in the male). Therefore, the total average of feeding intervals is kept rather constant.
3. Since May 19, 5 days before chicks' flying from the nest the female no more stayed in nest for night brooding. On May 21, she showed still some hesitation in flying off to roost, since after she had once flown to a building in the direction of the roost, returned to a tree near the nest where the male was perched. Then, with usual weak 'ka' note of roosting take-off, she flew off to roost followed by the male. On the next day, May 22, the pair, after resting a while billing each other and preening on the gingko tree near the nest, took off together directly to the roost, 29min. before the sunset at 1900 Lux.
4. Having slept in common flock-roost, the male and female returned together at 4.02 a. m. to their territory 30min. before the sunrise (4.31 a. m.) in the dark of twilight of 0 Lux, flying low through the buildings, 20m. apart each other, and thrusted themselves like an arrow into the dark foliage under the nest tree. Then, they silently waited a while until 4.15 a. m., 15 Lux, when the male first uttered 'ka ka ka ka, ' to which the female replied and each bird began its own morning schedule, keeping communication with 'ka ka' notes until it got light.
5. In this period of later nestling stage, the female was as nervous as to suddenly fly off for defense with food in her bill, if she perceived a trespassing other crow while she was feeding, and the male took much more conservative attitude, sometimes not showing apparent response to the trespasser.
6. The female's (rarely-once-also male) soft nasal 'nga' note toward nestlings became frequent as the chicks grow near to leave the nest.
7. The timing of the female's above attitude toward grown chicks near their flying from the nest and her change of roost from night-brooding to roosting take off from nest site, may be a series of correlated behaviors.