A 30,000-km journey by Apus apus pekinensis tracks arid lands between northern China and south-western Africa

This study, conducted by a multi-national team, followed 25 pekinensis Swifts on their annual migration cycles between 2014 and 2018. Birds were captured at their breeding site, the Summer Palace in Beijing, and fitted with geolocator tags. These small devices record day length and solar noon, allowing researchers to calculate the bird’s global position through time.   

After leaving Beijing in the middle of July, the Swifts headed north-west into Mongolia, before travelling west, re-entering China and crossing into central Asia. From there, the birds migrated to north-east Africa, flying over the Red Sea around the middle of August and reaching the longitude of the eastern Congo basin at the start of September. The final leg of their journey took the Swifts to their wintering grounds on the Southern African Plateau, where they remained from early November until mid-February.

Remarkably, their entire migration route tracked arid land, despite this requiring a longer journey. This is specific to the pekinensis subspecies and may be a relict of the Swift's population expansion after the last ice age, when the birds spread over a wider region via arid habitat.  

The Swifts' return to Beijing in spring was significantly shorter in time and distance than their autumn migration, with an average of only one stopover site on the flight north compared with four on their southward journey. This difference in spring and autumn migration is widely reported in other species and subspecies, including apus Swifts. 

However, the study also revealed some key differences between the subspecies. Compared to apus Swifts, pekinensis birds had a significantly longer breeding period, a shorter wintering period and a slower migration speed. Swifts breeding in Beijing travel an amazing 30,000 km each year - nearly twice as far as their apus counterparts breeding in northern Europe. As well as tracking arid habitat on migration, pekinensis Swifts also favoured more arid habitats on their winterng grounds than apus birds, suggesting the two subspecies are dependent on different food resources outside the breeding season.

This study sheds light on the different adaptations of subspecies, and may prove invaluable in understanding how migration routes arise and how populations ultimately diverge, at a time when many migrant species are under threat.