In one of the longest migrations ever recorded by a land bird, a cuckoo flew over 12,000 kilometres from Zambia in southern Africa to its breeding ground in Mongolia. Scientists are stunned at the 'mammoth journey' that involved Onon crossing 16 countries, and battling many hurdles on the way. He reached the Church Bird Banding Station in Mongolia on Wednesday, according to bird conservation organisation Birding Beijing. To monitor long distance migration, five cuckoos were fitted with satellite tags in June 2019 by scientists from the Mongolia Cuckoo project. Onon is the only one that has since completed a round trip from Mongolia to his winter home in Zambia and back again, covering a total of 26,000 km. Onon travelled at an average of 60km/h across Bangladesh, Kenya and India.