Complex sentence: These birds migrate from Russia, China, Siberia and few other adjoining European countries.Number of these migratory birds arriving here every year is reported in thousands but this number is declining over period due to various climatic hazards and economic exploitation of the Pond.
Split into simpler sentences: These birds migrate from Russia, China, Siberia and few other adjoining European countries. Numbers of these migratory birds arriving here every year are reported in thousands but this number is declining due to various climatic hazards and economic exploitation of the pond.