Nocturnal Bird Migration in Beijing

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 and Common Cuckoos, to Africa.  Some of these 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 simple sound recorder, it’s possible to gain an insight into the volume and diversity of birds flying over Beijing at night.

Birding Beijing, in collaboration with the Asian Infrastructure Investment Bank and Peking University, began a pilot project to record bird sounds at night in autumn 2021 from the roof of the Asian Infrastructure Investment Bank.  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 and it is ongoing today. 

The results of the 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.  The seminar culminated in the signing of a letter of intent between AIIB and the Beijing government to share the data from the project and to integrate the findings into land management practices.

The primary aim of the project was to raise awareness of the scale of nocturnal bird migration over China’s capital, especially the volume and diversity of species that fly over the city as its residents sleep, recognising that awareness is the first step towards building pride and public support for policies and measures that protect these birds and the places they need. 

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.  The location of the 15-storey AIIB headquarters is ideal for recording nocturnal flight calls as it is situated immediately south of one of Beijing’s largest parks, the Olympic Forest Park, not close to any major road and free of air traffic.

A photograph of Beijing taken from the Chinese Space Station, Tiangong, on the night of 24 August 2021 (the night we began recording). Image by Taikonaut Nie Haisheng, annotated with the recording location by Terry Townshend.

To analyse the recordings, we use Audacity, free-to-download software, to create spectograms of each hour-long audio file and used the ‘labels’ function to log and, where possible, identify each call.  The label files are then imported into Excel to produce a database of all call events with associated date, time, number of calls and, where possible, an identification.

An example of the visualisations (spectograms) that can be created from the calls of birds. Olive-backed Pipit and Eurasian Skylark are two of the most frequently recorded species at night over Beijing.

At present, all files are 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)

For a running total of species and volume of calls, see below:

NFCs in Beijing – species list by volume running totals

 

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, James Lidster, Magnus Robb, Seán Ronayne and Joost van Bruggen, to whom we owe a debt of gratitude.