There is a whole area of demographic studies – the chronoecology. It is connected with the cyclical nature of virtually all processes in the evolution of the population. In addition to the vector process (a constant growth of the world's population), which has created a strong concern and this phenomenon has been included into the list of the global environmental problems of mankind; cyclic processes of the population change were also revealed. The paper considers the cyclical birth-rate index in Fennoscandian countries during the long - term investigations. There is a steady negative trend of the birth-rate index, especially in Sweden. The spectra of periodic components, that form the long-term dynamics of the birth rate, are built. Specific to these countries, 170-, 50-60- and 15-17- year cycles are determined. The author speculates upon the internal causes and possible external pacemakers of these fluctuations. A comparison of the spectra of the periodic constituents of the birth-rate indices in Fennoskandia and Romania, as a more southern country, has been made. For the population cycles of fertility, the time external sensors can be manifested in individual fluctuations of the North Atlantic oscillation (NAO) in Scandinavia, as well as the harmonic components of the spectrum of the Nordic index (SCAND), the primary focus of which is situated over Scandinavia. The first oscillation of this global climate index can maintain the stability of the 170-year cycle of birth-rate; and the second one is responsible for the 60- and 40-year rhythms that function in Scandinavian countries, but they are absent in southern Europe (Romania).
Keywords: the birth-rate index, dynamics, cyclicity, spectrum, harmonic components, Fennoscandia, multi-year rhythm, time sensor.