Comparative analysis of breeding rates of rural and urban grey starling colonies in Tokyo area: The second report (Part 2)

Abstract

Summary The rates of clutch size, brood size and brood‐size fledged recorded during the period 1956≈63 (2 years interrupted) in the rural and the urban colony of the grey starling were analysed comparatively. The clutch size was significantly larger in the urban than in the rural one and the brood size was also larger significantly in the urban population. But, the difference in brood‐size fledged was insignificant. This reflected that the hatching rate was similar in both colonies (the rates in total differed but possible unusual rate was included in the clutch size of 5 eggs) and this may be determined physiologically but not depending upon food supply since smaller clutches showed higher hatching rate. However, the fledging rate was higher in the rural and lower and more variable in the urban colony. This is apparently due to food which was nutritive animal food in the rural but largely mixed with fruits in the urban. The fledging rate was rather irregularly variable with brood size suggesting that this is dependent upon parents' adaptability in feeding. However, the rate of 100% fledging becomes higher from brood sizes of 6 and less chicks. Thus, in general larger clutch and brood sizes produced larger absolute numbers of chicks and chicks fledged respectively. But, 5 was the most frequent size in the clutch and brood sizes and 4 in the brood‐size fledged. From the above, the ecological evolution of urban population was discussed.