Onon is an unassuming bird. Like all adult common cuckoos he’s pigeon-sized and dressed in dull, blue-grey plumage with a dollop of flair provided by his boldly barred belly and outer tail feathers. Keen birders would certainly notice Onon if he were to perch or swoop close by, but most people would likely overlook the unremarkable bird. But Onon is anything but average.

Common cuckoos (Cuculus canorus) lack the dazzling emerald colours of some others in the family, but they make up for it with incredible feats of navigation and endurance. Image © Ron Knight

The cuckoo has just completed one of the longest migrations recorded by any land bird. Onon set off from his winter home in Zambia a little over two months ago. Since then he has crossed an ocean, survived savage winds and traversed multiple countries on an arduous voyage to his breeding grounds in Mongolia.

It has been a “mammoth journey” say the team of scientists who fitted Onon and five of his cuckoo compatriots with satellite tags last year to track their migratory movements. The research, led by the Mongolia Cuckoo Project - a joint venture between local scientists and the British Trust for Ornithology (BTO), aims to gain a clearer picture how and why birds like cuckoos undergo such long-haul flights.

Onon’s satellite tag was fitted in June 2019 at the Khurkh Bird Ringing Station in southeastern Mongolia. His name is borrowed from the Onon River which flows north of where he was tagged. In just under a year, the resilient cuckoo has completed a round-trip of about 26,000 kilometres (16,155 miles) – a trek that has included 27 border crossings between 16 different countries.

Here's a look at the movements of the five tagged cuckoos. Onon is in green (zoom in for more detail):

Data from the return leg of his journey shows that he flapped his way across thousands of kilometres of the Indian Ocean without stopping. Flying at an average speed of 60 kmph (37 mph), he crossed over the sprawling plains of Tanzania and Kenya, and into Somalia which served as his launchpad for crossing the Arabian sea. From there, it was a quick flight over India and Bangladesh, a dash across a stretch of Burma and into China before heading north to Mongolia.

Having completed this feat of navigation and endurance, Onon has “no time to waste as he needs to set up his territory, defend it from competing males and mate with as many females as possible!” the research team explain on their website.

Although four other bids were tagged in the project, Onon is the only one to have successfully made it to his destination. Another of the tagged cuckoos, named Bayan, is believed to have succumbed to exhaustion or poaching somewhere in Yunnan, China having flown all the way from Mt Kilimanjaro in East Africa. Bayan clocked 10,000 kilometres in two weeks and was likely too tired and hungry to effectively protect himself.

Onon was the only of the five tagged cuckoos to complete his journey. Image © The Mongolia Cuckoo Project

"I think the big takeaway is that the birds are able to travel so far and often so fast that they must be able to find suitable conditions for fattening and also know exactly where to go to get favourable wind conditions to help them, for instance, to cross the Indian Ocean," BTO’s Chris Hewson told the BBC.

While the costs of migration may not be as great as ornithologists previously suspected, a journey of this magnitude is certainly fraught with risks. Everything from bad weather and starvation, to predators and poachers can prematurely end the trip.

For Dr Hewson – and many others who tracked the cuckoos online – there is something reassuring about their epic journeys. At a time when humans are grounded as a result of COVID-19, there is a certain satisfaction in vicariously travelling half way around the globe on the back of a bird – a sense of comfort in knowing that natural rhythms continue to churn along in our absence.

Image © Mike Mckenzie8