The comparative analysis of breeding rates of rural and urban Grey Starling colonies in Tokyo area

Abstract

1. Following the previous paper for 1956-57, comparative results of breeding at two nest-box colonies of Grey Starling were discussed based on the data of 1956-1963 inclusively (1958 and 1962 lacking).2. Correlations of weather, especially temperature, with the frequency of start of egg laying were analysed from the average laying dates and the earliest laying dates.3. Annual variation of the average laying dates paralleled at two colonies and this suggested the correlations with the temperature in the later part of April.4. The significance of the earliest laying dates were discussed and analysed, and the temperatures during 10 days before the laying were considered as critical, since they were most constant in different years and localities. The warmth sum and sunshine hours were also given.5. Food was regarded not as a timing factor but as a regulating nutritive factor of breeding and discussions were given from this point of view.6. Annual earliest egg laying dates were significantly a few days earlier at urban than rural colony and this was supported by always slightly (0.2-2.7°C) higher 5 days means of average temperatures at the urban area.7. The psychological factors which modify the timing of actual egg laying after egg laying temperature threshold is reached were discussed based on observations.8. Clutch size was significantly larger at urban than rural colony and this may be correlated with entirely different food supply. The urban food was much more miscellaneous with animal and plant (fruits) species.9. After the nest-boxes were attached there was noticed a common tendency at two colonies that the percentages of local maximum clutch sizes rose in the 2nd to 3rd years and decreased in the 4-5th years, thus suggesting the population turnover of age classes.10. At both colonies larger clutches tended to be laid at the beginning and smaller ones towards the end of the season. The reason and possible evolutionary significance were discussed.