Have you ever wondered what birds are flying over your home at night? If you are on any sort of flyway, during the migration season it is possible that many hundreds, even thousands, of birds fly over your home in a single night. Recording sound during the dark hours can help to shed light on the number of birds and the diversity of species that are flying overhead as we sleep.
The practice of recording nocturnal flight calls (NFC) is gaining in popularity in Europe and the US (and elsewhere?) but is still in its relative infancy. Even with little knowledge of individual species’ calls, it is possible to gain an insight into the volume of birds that call as they pass overhead.
Of course most birders are also interested in identifying the species, but identification of the calls can be a challenge. Not only does successful ID require a strong knowledge of the vocalisations of many of the resident and migratory species in the area but it appears that some species use different calls at night to those with which we are familiar, thus adding to the difficulty. Lots of work is underway, including at Cornell Lab, to use AI to help scan recordings to identify the species but, for now at least, in East Asia that is a long way off.
With Beijing situated on a major flyway for birds commuting between Siberian breeding grounds and non-breeding grounds in China, SE Asia, Australasia and even Africa, there simply *must* be lots of nocturnal migration over the capital so, back in autumn 2017, living on the 13th floor of an apartment building at the time, I made my first attempts at nocturnal recording from my window. Using a simple digital recorder, I was able to record species such as Olive-backed Pipit (Anthus hodgsoni 树鹨 Shù liù), Eurasian Skylark (Alauda arvensis 云雀 Yúnquè), Great Bittern (Botaurus stellaris 大麻鳽 Dà má jiān) and Siberian Rubythroat (Luscinia calliope 红喉歌鸲 Hóng hóu gē qú). That experiment gave me a tantalising glimpse into the nocturnal migration over my apartment but a subsequent move to an apartment much less suitable for recording meant that the potential remained unfulfilled.
Fast forward to summer 2021 and, in a conversation with Sir Danny Alexander, Vice President of the Asian Infrastructure Investment Bank (AIIB), we hatched an idea to begin a recording project on the roof of AIIB’s headquarters. The building, 15 storeys high, is in a great location for such a project. It is immediately south of the Olympic Forest Park in the north of the city, not close to any major roads, suffers very little from aircraft noise and with almost no tall buildings close by.
We purchased a Wildlife Acoustics Song Meter Mini (weatherproof and programmable), and set it up on the roof, programming it to begin recording from 24 August until mid-November. The recorder is perfect for this project as the only maintenance needed is a change of batteries every two weeks or so. The recorder automatically adjusts the recording time to allow for the changing sunset and sunset times and a 512GB memory card is capable of storing all the files for the whole period.
The primary objective of this project is to gain an insight into the volume of birds flying over central Beijing at night. With identification of most calls straightforward, we hope to be able to gain an improved understanding of the timings, including peaks, of individual species and potentially also the relationship between weather patterns and the extent of migration. Given the impressive volume of calls, we are already building up a large file of “unidentified calls” and, with the help of birders in the region and experienced ‘nocmiggers’ elsewhere, we hope to identify as many of the unknowns as possible.
The files from the first few weeks of recording have been downloaded and we are beginning to analyse them. It’s a time-consuming process to go through them all but using the excellent free sound analysis software, “Audacity“, to produce spectograms in order to ‘visualise’ the files means it’s relatively easy to find the bird calls and skip through periods of silence.
More than 4,000 calls have been identified so far. Perhaps not surprisingly, in late August and September, the most dominant species have been Common Rosefinch (Carpodacus erythrinus 普通朱雀 Pǔtōng zhūquè), Olive-backed Pipit (Anthus hodgsoni 树鹨 Shù liù) and Eurasian Skylark (Alauda arvensis 云雀 Yúnquè) but these have been supported by a good selection of other species including Black-crowned Night Heron (Nycticorax nycticorax 夜鹭 Yè lù), Striated Heron (Butorides striata 绿鹭 Lǜ lù), Great Bittern (Botaurus stellaris 大麻鳽 Dà má jiān), Green Sandpiper (Tringa ochropus 白腰草鹬 Bái yāo cǎo yù), Common Sandpiper (Actitis hypoleucos 矶鹬 Jī yù), Wood Sandpiper (Tringa glareola 林鹬 Lín yù), Common Redshank (Tringa totanus 红脚鹬 Hóng jiǎo yù), Eurasian Curlew (Numenius arquata 白腰杓鹬 Bái yāo biāo yù), Forest Wagtail (Dendronanthus indicus 山鹡鸰 Shān jí líng), white-eye sp. (Zosterops sp., 绣眼鸟 xiù yǎn niǎo), Yellow-bellied Tit (Periparus venustulus 黄腹山雀 Huáng fù shānquè), and lots of thrushes and Muscicapa flycatchers (still to be identified to species).
You can follow the progress of the project at this dedicated page, where we will upload good examples of calls, a batch of unidentified calls (on which we welcome suggestions!) and, in due course, some statistics about the volume of birds each night and a full species list. Analysis of all the files probably won’t be completed until well into 2022 but we are already excited about what this project will reveal about nocturnal bird migration in Beijing.
Huge thanks to the AIIB team, in particular Sir Danny Alexander, Alberto Ninio and Li Zeyu, for their support for this project and for their ongoing help and assistance. And thank you to David Darrell-Lambert for initial advice about NocMig and to Geoff Carey and Paul Holt for advice and assistance with identifications. Thanks also to all the birders in the East Asian Bird Vocalisation WeChat group and the NocMig WhatsApp group for help and assistance.
For the latest news about this project, to hear some of the calls we are recording and for a list of unidentified sounds, please see this dedicated page.
Header image: The Wildlife Acoustics Song Meter Mini in place on the roof of the Asian Infrastructure Investment Bank (AIIB) in Beijing.