To see the paper about the Beijing nocturnal bird migration study published in Bird Conservation International in June 2024, see here.
Background
One of nature’s most incredible spectacles happens right over Beijing as we sleep in our beds at night. In spring and autumn millions of birds fly over China’s capital city between breeding grounds in Siberia, Mongolia and north China and non-breeding grounds in south China, SE Asia, Australasia and even, in the case of Beijing’s Swifts, Common Cuckoos and Amur Falcons, to Africa. Some birds migrate during the day – for example, the larger soaring birds such as birds of prey, cranes, storks etc that use the sun’s energy to assist their flight. However, the majority of birds (around 80%) – especially the smaller species – migrate at night. This is because there are fewer predators active during the dark hours, the weather tends to be cooler and more stable and some birds navigate using the night sky.
Some birds vocalise as they migrate – to keep in touch with each other as they fly and, towards the end of the night, attempting to initiate responses from their own kind on the ground, which could indicate a safe place to stop for the day. This means that, using a simple sound recorder, it’s possible to gain an insight into the volume and diversity of birds flying over Beijing at night.
Wild Beijing, in collaboration with the Asian Infrastructure Investment Bank (AIIB) and Peking University, began a pilot project to record bird sounds at night in autumn 2021 from the roof of AIIB. During the period 25 August to 2 November 2021 we recorded more than 34,000 calls from at least 60 species. The success of the pilot project encouraged us to continue the recording. As of September 2023, four complete seasons (autumn 2021, spring 2022, autumn 2022 and spring 2023) have been processed with 84,890 calls logged.
The results of the autumn 2021 pilot project were presented to a special seminar at the Asian Infrastructure Investment Bank on 27 September 2022, hosted by Vice President Sir Danny Alexander and including speakers from Peking University and the Beijing municipal government.
We use a Wildlife Acoustics Song Meter Mini as it is weatherproof, capable of storing sound files for the whole period on a 512GB memory card, and programmable – automatically adjusting the recording time to account for the changing sunset to sunrise.
All files were analysed manually but it is hoped that, in future, AI software can be ‘trained’ to recognise species in East Asia. We have begun a collaboration with Cornell Lab of Ornithology to train the system they have developed for North American birds with the calls from birds of East Asia. Automated processing of the audio files will make it easier to analyse recordings from multiple locations in each season which, in turn, will help us to build a better picture of the scale and diversity of bird migration over Beijing and also to help us to understand patterns and potential correlations, for example between the number of calls and varying levels of light pollution across the city.
For a summary and detailed results from each season, please click on the links below.
Autumn 2021 (25 August to 2 November 2021)
Spring 2022 (15 March to 8 June 2022)
Autumn 2022 (18 July to 10 November 2022)
Spring 2023 (15 March to 8 June 2023)
For a running total of species and volume of calls over the four seasons, see below:
Acknowledgements
This project would not have been possible without the wonderful team at AIIB, including Sir Danny Alexander, Alberto Ninio, Li Zeyu, Tian Hua and Yan Bo. The team at Peking University, led by Assistant Professor Hua Fangyuan, and including 张棽 (Zhāng Shēn), 任晓彤 (Rèn Xiǎotóng), 刘双祺 (Liú Shuāngqí) and 杨晓彤 (Yáng Xiǎotóng), has been a joy to work with and I look forward to continuing cooperation. Andrew Farnsworth at Cornell Lab has provided valuable advice and encouragement and we look forward to working together with him and his team, especially Benjamin Van Doren, as this project expands. A number of people have helped with the identifications, including Jonas Buddemeier, Geoff Carey, David Darrell-Lambert, James Eaton, Paul Holt, 李觉非 (Lǐ JuéFēi), James Lidster, Magnus Robb, Seán Ronayne, Joost van Bruggen and Stanislas Wroza, to whom we owe a debt of gratitude.