Abstract
Observations were made on the breeding season in ring doves; 1, 400 intervals between clutches laid by 84 pairs of ring doves during about 14 years (1928-1941) were treated so distribute in every month of the year. An interval preceding any clutch laid in a certain month is considered to belong to the very month; for example if the first egg of a clutch was laid on Jan. 1 in any year an interval of 60 days, i. e., the first egg of the preceding clutch had been laid on Nov. 2 in the previous year, the interval belongs to January. Intervals of each month of the year were collected in this way, and the number of intervals or frequency of January was observed to be 98, and that of, February to be 103, and so on. The average interval of each month was calculated as, for example, that of January to be 60.41 days If we consider that the doves repeat the reproductive cycles in every 60.41 days as in January, the number of reproductive cycles per annum must be 6.40, and the writer considered this to be the reproductive capacity of the doves in Janary. And the reproductive capacity in every Month of the year is able to be calculated in this way. Thus, we can draw a curve of breeding or reproductive capacity of the year as shown in Fig. 1.The writer tried to draw curves denoting ann ual changes of atmospheric temperature, day-time length and ultra-violet radiation in Fukuoka on the same figure of the breeding curve, and made some considerations on the sexual periodicity and the cause which determines it.
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