Complex sentence: During winter months starting from mid-December, at certain seasons, as many as 40,000 birds congregate in this bird sanctuary and some birds come from Siberia, Latin America and parts of north India.
Split into simpler sentences: During winter months, starting from mid-December, as many as 40,000 birds congregate in this bird sanctuary. Of which, some birds come from Siberia, Latin America and parts of north India.