Observations of territorial life in breeding season of a pair of Jungle Crow Corvus macrorhynchos in City Tokyo

continued 4: Additional observations in 1970

Abstract

This is additional observation records of 1970 of a breeding pair of Jungle Crow Corvus macrorhynchos and chiefly supplements the lack of 1969 observations in early incubation period.
1. In 1970, probably the same pair remained in the same territory of 1969. On March 27, the female was found incubating, unexpectedly in a Ligustrum about several meters from the ground, not high up in the big gingko tree as in the previous year.
2. In early incubation period (2nd-3rd days), the incubation rate of the female was 68-70%, with average 20 minutes sessions and 7-8 (longest minutes 16, 22) minutes recessions. In a case of middle incubation period (14th day), the rate increased to 75%, with 15-42 (av. 29.3) minutes cessions and 5-10 (av. 7) recessions. In later period (19-20th days), in short evening observations, the incubation rate further increased to 76-86%, with 15-32 (av. 19) minutes sessions and av. 2-3 minutes recessions.
3. The trespass intrusion over territorial border of wandering, apparently young, pairs or solitary crows were frequent, especially during early incubation period. These were not so strongly defended (often only watched by male), but those intruded over territory within about 400m from nest site were positively chased away by male with cooperation of female, and once, when the female was away from the nest, a crow succeeded to thrust himself deep to the center of territory attracted by old (1969's) nest in gingko tree, but was violently attacked by female and chased away by male (see Kuroda, Misc. Rep. Yam. Inst. Nos. 37/38: 548).
4. The territory trespass of wandering crows was most frequent during the morning and in total 9 cases of 21 birds on March 28 and 6 cases of 11 birds on March 29 were recorded during 7.30-12.08 a. m. (278min.) and 6.45-9.07 a. m. (137min.): therefore 1.98 times and 2.64 times per hour respectively. But at noon, March 29, 12.40-15.42 p. m. (182min.), there was only one case of trespassing.
5. On April 9 (14th day of incubation), there were still 4 cases, 6 birds of trespassings, during 5.05-7.01 a. m. (116min.), 2.04 times per hour, but no case was observed on May 1 (14 days after hatching) between 8.45 a. m. -12.02 p. m. (197min.) and only 2 cases on May 2, 4.45-6.29 a. m. (104min.) (1.15 times/h).
6. However, the female's defensive impulse is raised toward later incubation to nestling periods. Thus, the female would suddenly fly out of the nest, with attacking notes, to chase the intruders away, and on April 9 even flew to distant (750m. from nest) territory border. Moreover, she was observed on May 1 and 2, to chase smaller birds, the bulbul Hypsipetes amaurotis and blue-winged magpie Cynopica cyana from last year's nesting tree adjacent to her nest tree of this year.
7. On the other hand, the male, who often positively defended by pursuing trepassers, even by aerial fighting in some cases, during early incubation period when the female closely sat in nest without noticing the trespassers, got conservative in defense as the female's defensive attitude was strengthened toward later incubation period, and now he only assisted her or watched her with warning notes. He was even indifferent to trespassers if he was busy in his job of food searching.
Thus, the territorial defense of the pair was well balanced to be effective according to the breeding stage, territorial maintenance and food securance in correlation with the sexual division of labor.
8. In incubation period, especially early in the morning, the male works hard for food search widely, but usually within about 400m. from the nest, to prepare stored food on buildings, under eaves of houses, or in trees (hidden by plucked leaves) and under stone (hidden by fallen leaves).