On the basis of long-term works in Selenga river delta (1973–80) and Irkut river mouth (1983–1987) the analysis of seasonal and interannual variability of clutch size in Asian Dowitcher was carried out. Its variability is caused by the several factors poorly influencing average clutch size. Seasonal variability (for pentades) is not expressed and shown only in case of high nest loss and a plenty repeated (compensating) clutches. However and in such cases the average clutch size in first- and last five-day is statistically doubtful also it differs enough high stability. The mass nest loss during the short period (2–4 days) causing disturbance of reproductive processes in particular pairs, causes well expressed «compelled» nesting parasitism, occurrence of three egg clutches and increase amount of nests with one egg instead regular two egg clutches. It results in essential change of a ratio of nests with different egg amount and increase of interannual variability of average clutch size. Hence, alongside with other factors, environmental conditions of particular region can render the certain influence on fecundity even in species with the determined clutch size.