[in Japanese]

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Chick feeding^* The growth of nestlings is subject to parents' feeding rate, which is influenced by: 1. chicks' age 2. brood size 3. weather 4. time of day 5. necessary amount and kind of food 6. availability and distribution of food 7. parents' division of labor and sexual difference in feeding, etc. These factors are correlated and work to set the feeding interval and feeding frequency (per hour) which can be observed and recorded for statistical analyses.
Here, these are discussed in relation to chick age and time of the day and are shown by Figs. 10-15, and Tables 8, 9.
Overall feeding rate: In total of observation, the feeding interval ranged from a few minutes to over an hour, in total 3-76 (av. 32.7) min. in the female, 4-104 (av. 40.17) min. in the male and 0-68 (av. 17.95) min. by both sexes. With 3 chicks, the deeding frequency/per hour was 2.08 (0.70/per chick) times in female, 2.01 (0.67/per chick) times in male and 3.68 (1.24/per chick) times by both parents.
Feeding rate by growth of chicks: The female's feeding interval at hatching of chicks is average as long as about 40 minutes (because the naked chicks need to be brooded) and is shortened with the chick growth to about 20 minutes at around 30th day after hatching. But, again the interval is lengthened to about 25-30 minutes. This decrease of feeding rate by the female may support the supposition that by doing so chick's overgrown body weight can be lessened to prepare for flying from the nest (actually the female has been observed to invite the chicks for flying by keeping them hungry).
The feeding frequency also increased from 1.2 times/hour at early period through about 2.7 times/hour at about the age of 30th day and then decreased to about 2.5 times/hour.
In the male, in contrast, the feeding interval at early period was as short as about 25 minutes (as compared with 40 minutes of the female), thus supplementing female's long intervals (by brooding chicks). Then, as the male becomes busy in food search and storage, its feeding interval is extended to average 45 minutes, thus longer and variable than in the female.
But, the combined feeding intervals by male and female are kept constant at the level of between 15-20 minutes intervals, reflecting the sexual behavioral compensation toward a stable feeding rate, adapted to the chick growth of the brood size (in this case 3 chicks). The same is true with the feeding frequency where the male feeds chicks with higher frequency than the female in early nestling period, but later it was kept at lower frequency with higher variaton than in the female, and the female's feeding frequency (though at first lower than in the male) becomes steadily higher toward later nestling period (according to the chick growth) until about 30th day after hatching to be dropped before chicks' flying from nest.
These differences in feeding rate curves by male and female during chicks' growth from hatching to flying, can be more clearly shown by dividing the nestling period into: 1. early (a few days after hatching) 2.middle (between about 10-15 days after hatching) 3. later (between about 16-29 days after hetching) and 4. final (from 30 days after hatching to flying from nest at about 34-36th day) periods (see Fig. 12).
Feeding rate by time of day For this analysis, the activity hours were divided by 2 hour periods from 4.00-6.00 a. m., 6.00-8.00 a. m., 8.00-10.00 a. m., 10.00 a. m. -12.00, 12.00-14.00 p. m., 14.00-16.00 p. m. and 16.00-18.00 p. m., and all the records of feeding intervals (irrespective of nestling age) were tallied by sexes. In this analysis, the mean (M), range (R), standard deviation (σ), variance indices (c₁=σ/M%, c₂=σ/R%) were calculated and shown in Figs.

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