Citation
Overview
The Swift is widely distributed with a cross-continental breeding range spanning Europe and large parts of Asia and north Africa. Until recently, Swift migration research has focussed on populations which breed in Europe and north-western Africa (the apus subspecies), leaving the migration of birds breeding throughout Asia (the pekinensis subspecies) shrouded in mystery.
In more detail
Acknowledgements
The authors are grateful to all the volunteers taking part in the fieldwork. They also appreciate the support from Management office of Summer Palace and Beijing Wildlife Rescue & Rehabilitation Centre, and the help from National Bird Banding Centre of China and Beijing Bird Banding Station. They are very grateful to the three anonymous reviewers and an associate editor for their constructive comments and suggestions.
Funding
This study was supported by SHAN SHUI Conservation Centre, Beijing, the research grants from the Swedish Research Council (621-2013-4361, 2016‐03625) to SÅ, and a Dulverton Trust grant from British Trust for Ornithology to CMH. The geolocators were funded by Action for Swifts (DN) and by SÅ at Lund University covered by funds listed above, with at least one logger donated by Migrate Technology Ltd.
Abstract
Background
As a widely distributed and aerial migratory bird, the Common Swift (Apus apus) flies over a wide geographic range in Eurasia and Africa during migration. Although some studies have revealed the migration routes and phenology of European populations, A. a. apus (from hereon the nominate apus), the route used by its East Asian counterpart A. a. pekinensis (from hereon pekinensis) remained a mystery.
Methods
Using light level geolocators, we studied the migration of adult pekinensis breeding in Beijing from 2014 to 2018, and analysed full annual tracks obtained from 25 individuals. In addition, we used the mean monthly precipitation to assess the seasonal variations in humidity for the distribution ranges of the nominate apus and pekinensis. This environmental variable is considered to be critically relevant to their migratory phenology and food resource abundance.
Results
Our results show that the swifts perform a round-trip journey of ca 30,000 km each year, representing a detour of 26% in autumn and 15% in spring compared to the shortest route between the breeding site in Beijing and wintering areas in semi-arid south-western Africa. Compared to the nominate apus, pekinensis experiences drier conditions for longer periods of time. Remarkably, individuals from our study population tracked arid habitat along the entire migration corridor leading from a breeding site in Beijing to at least central Africa. In Africa, they explored more arid habitats during non-breeding than the nominate apus.
Conclusions
The migration route followed by pekinensis breeding in Beijing might suggest an adaptation to semi-arid habitat and dry climatic zones during non-breeding periods, and provides a piece of correlative evidence indicating the historical range expansion of the subspecies. This study highlights that the Common Swift may prove invaluable as a model species for studies of migration route formation and population divergence.
