TEHRAN Thousands of migratory birds arrive in Gaavkhouni marshlands and Zayandeh Roud (Zayandeh river) in the central Province of Isfahan. The birds are to spend the winter in the area. They migrate to the region from the cold areas inside and outside Iran every year in late November. Gaavkhouni marshland, located east of Isfahan, is among the 18 registered international marshlands.