Have you ever wondered what birds are flying over your home? During the migration season it is possible that many hundreds, even thousands, of birds fly over one’s home in a single night and 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. Thus, identification of the calls recorded is a major 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 birds use different calls at night to those with which we are familiar, thus adding to the difficulty.
For some time, I’ve been thinking that I really should try to record nocturnal flight calls in Beijing. After all, although I live close to one of the world’s busiest airports (a source of ‘noise’ for around 20 hours per day), my apartment is on the 13th (top) floor and, from sightings in the capital, we know that Beijing is on a major flyway. There simply *must* be lots of migrants flying over my apartment as I sleep…
And so, after some helpful advice from David Darrell-Lambert in London, who has been recording night flight calls for some time in an urban environment, I took the plunge and ordered a digital sound recorder and set to work! I made my first recording on the night of 29/30 August and have been recording every night that I have been at home ever since.
So what have I discovered? A resident LITTLE OWL that I never knew I had, some BLACK-CROWNED NIGHT HERONS, MOORHEN, GREY NIGHTJAR, brown flycatcher sp, a probable EYEBROWED THRUSH, YELLOW-BROWED WARBLER, OLIVE-BACKED and RICHARD’S PIPITS, LITTLE BUNTINGS and many many many calls that remain unidentified!
Here are the spectograms and recordings of MOORHEN and the presumed EYEBROWED THRUSH. Note the “noise” of the local crickets, particularly in the first recording.
That’s not a bad list of species for a major capital city and I am confident I will record many more species as the autumn wears on. What price a first record for Beijing?
So how does it work?
The digital recorder records to a HCSD memory card. Depending on the quality, a 16GB memory card can record around 20 hours of sound. I simply place the recorder on my window ledge (or on the roof), pointing roughly in a northerly direction, and leave it there until early morning. When I wake I have around 8-10 hours of recording.
Fortunately, one doesn’t need to listen to all 8-10 hours to find the birds. There is some great free software out there to help. Audacity and Cornell Lab’s RavenLite are both superb pieces of software that help to “visualise” the sounds using a spectogram. I upload the sound file from the memory card to RavenLite and set the programme to display 10 seconds at a time… then I scroll through the file, spending a fraction of a second on each page, until I see an obvious bird call. For my urban environment, I very quickly became accustomed to identifying barking dogs, car horns and people shouting, enabling me to scan the files with ever greater efficiency. I perhaps spend around an hour going through each night’s recording and saving all the relevant snippets. So far, on average, I have recorded around 30 calls per night, around two thirds of which remain unidentified.
To help with identification, the great resources at Xeno-canto Asia are a big help. However, even this resource is generally limited to diurnal calls and may not include calls given exclusively at night.
It is clear there is a huge amount to learn, and discover, by recording nocturnal flight calls and I am sure that I am going to find out an immense amount over the autumn migration period.
A dedicated page has been set up here where all the latest news about this exciting new project will be posted. Please check regularly and help if you can!
Title image: a spectogram of EYEBROWED THRUSH recorded from my apartment.