The pre-war population of Collared Turtle Dove, Streptopelia decaocto, occupied a rather restricted area, particularly around Koshigaya, in Saitama and parts of adjacent prefectures. After the war, since 1945, it was recklessly shot to the danger of near extinction. In 1948, Udagawa estimated its number as about 60 birds within an area of 2km radius, and it may have been still more reduced later, perhaps to less than 20. However, soon it became protected as a natural monument and the 'prefectural bird' and then showed a steady increase in number.
After 20 years, the author made 21 population censuses by random search method during a period of 1967, Oct. and 1968, June (with 10 more supplemental post-breeding counts of July to Oct., 1968). Its number could be totalized as 580 birds. But, if 86 singing males recorded are regarded as paired breeders, 666 birds may be more accurate. Moreover, when the result of the census made in 1966 by local middle school biology group within its main populated area is considered, the total population may have been at the least 700 birds in 1968. This means about 12 times increase after 20 years. The area of population range was confirmed as 90km2 within the total area of 146km2 censused, and this is about 7 times spread from the original range in 1948. There are some concentrated areas in the main population range where the density is up to 15 birds/km2 but in the peripheral areas of recent range expansion, the density is more or less 1-2 birds/km2, the average being 6.4 birds/km2 within the total population range. The population counts of main (not total) populated areas had been made in 1959 (141 birds), 1961 (206 birds), 1963 (193 birds), 1966-67 (399 birds) and 1966 (552 birds), by Koshigaya Nishi Middle School and by Mr. Kosugi. Considering these data, a population growth curve is presented.
