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 can be seen in the daytime – 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 – 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 many 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 primary aim 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.  If successful, automated processing of the audio files will be possible, making 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, see below:

NFCs in Beijing – species list by volume running totals