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Nocmig: A beginner's guide

I find bird migration fascinating and, despite being based well away from the coast, I have developed a particular interest in trying to observe this intriguing natural phenomenon. It is amazing what you can see and hear in one given place as you wait for the migrating birds to come to you. ‘Vismig’ (visible bird migration), sometimes called sky-watching, involves observing overhead diurnal migration and can be carried out from any particular location with a good view of the sky (I watch from my back garden). In peak autumn season this can produce the spectacular scene of thousands of birds passing over in a short period of time, as well as the chance of spotting scarce and rare species which wouldn’t ordinarily be seen in that location.

However, this spectacle is not just limited to these day time migrants as many birds are in fact nocturnal migrants. This is particularly evident on the coast when an overnight ‘fall’ has produced trees dripping with Goldcrests and bushes full of ticking Robins and Song Thrushes, when there had seemingly been few the previous day. I had long been aware of nocturnal migration, and similar to most birders regularly heard the ‘tseeping’ Redwing calls at night every autumn. But what else is up there in the dark and how can this ‘nocmig’ be observed?   

Nocturnal flight call (NFC) recording first became popular with birders in the USA; largely as a greater number of American passerine species produce nocturnal calls than their counterparts on this side of the pond. Nevertheless in recent years the detection method has grown a strong following among European birders. The process involves the use of sound-recording equipment to capture the flight calls of migrating birds, then detecting and identifying the call signatures using computer software. Migrating birds will often fly over the British Isles on a broad front and therefore you really do not need to live on the coast or on a migration flyway to give nocmig a go. There is the potential to record many different and perhaps unusual species for your given location. To illustrate this point, from my own recording location in Cambridge (pretty much as far inland as you can get in the UK) I have recorded Common Scoters, Pink-footed Geese and Sandwich Terns on multiple occasions; all of which are coastal species which are very rarely seen locally to me. 

Freshly arrived migrants: Redwing and Song Thrush are very common nocturnal migrants particularly in Autumn.

To start recording you will need to make a small investment in some sound-recording equipment. Essentially you will need a microphone and a device that saves the sounds which are recorded. This could simply be a mobile phone or a portable sound recorder (with inbuilt microphone). You will also need a computer and a pair of headphones to analyse your recordings. The team at the Nocmig website have produced a comprehensive comparison list of recording equipment, which details the advantages and disadvantages of each setup. My personal choice was to purchase a sound recorder (£100) with an additional microphone (£50) to improve the quality of my recordings. This setup has the particular advantage of being portable and therefore has dual use: I can take the equipment out with me when I’m birding to record other natural sound types.

Simple equipment options: a Mini USB microphone in pyrex dish (photo Simon Gillings), a portable sound recorder with windshield on a tripod (photo Nick Moran), a portable sound recorder in large bubble wrap-lined bucket to dull reverberations (photo Jon Heath).

When you have equipment ready, it’s time to wait for nightfall and start recording! Here are a few simple steps to follow:

1.     Check the weather forecast for appropriate conditions to record.

Windy nights will create ‘noisy’ recordings where bird calls are difficult to distinguish, and wet nights will risk damage to your equipment. The best conditions for nocmig are generally considered to be cloudy (which encourages the birds to fly lower) and calm. A change in wind direction is also thought to be a good cue for the onset of migration.

2.     Position your recording equipment in an exposed position, away from overhanging branches.

Overhanging objects may obscure the calls as well as cause unwanted background noise. You may also wish to orientate your recording equipment to face a particular direction, away from a noisy road or towards the anticipated flight path of migrants. Remember that you are leaving your equipment outside and unattended, so make sure it is in a safe and secure location.

3.     Press record and leave the equipment to run overnight.

It is so easy to forget or improperly press record before you leave your equipment (I have made this mistake numerous times)! It is also worth double-checking the recorder’s batteries are fully charged.

4.     The following day download the sound files created by the sound recorder overnight onto your computer.

Sound files are often quite hefty so you may need to manage storage space on your device and keep on top of files from previous nights recordings.

5.     Using a free software package called Audacity, open the sound files in spectrogram format.

The spectrogram (also called a sonograph) produces a visual representation of the recorded sound and allows you to pick out interesting noises among the background sound. There is some further info on how to configure Audacity and process the spectrogram on the Nocmig website.

6.     Now the fun bit! Scroll through the spectrogram generated by the sound recordings looking for any call signatures from last night’s migrating birds.

Identifying bird calls in the spectrogram against the various other obscure night time noises (barking dogs, squealing tyres, police sirens, fireworks) will take some practice. Also don’t be discouraged if you cannot identify every call – many will be too distant, distorted or unclear to successfully identify. Make sure to use resources such as the excellent xeno-canto website to compare your recordings with those made by other recordists.

Spectrogram generated in Audacity, with frequency (kHz) on the vertical axis and time (seconds) on the horizontal axis, showing call signatures of a selection of fairly commonly recorded nocturnal migrants.

Nocmig can appeal to birders of all disciplines; whether you’re aiming to add to your garden list, track migration or sharpen your bird call ID skills. It is also perfect for young birders as it can be carried out easily from home and also provides an opportunity to practically learn a variety of (not always common) bird calls – knowledge which will become invaluable in the field.

With perseverance, especially in the spring and autumn peaks of migration, you will be amazed with the diversity of species passing over. Sure, common species like Redwing, Song Thrush and Blackbird can be expected, but what about waders such as Green Sandpiper, Redshank, Whimbrel and water birds like Water Rail and Little Grebe? Yep, they’re up there and not uncommon, even over urban locations well away from water courses. As with vismig, there is always the potential for something a bit rarer, so keep an open mind to the possibilities and with persistence you may be rewarded.   

Are there Whimbrel flying over your house at night? You’ll have to give nocmig a go to find out...

This blog was written by Jonathan Heath. Jon is a Cambridgeshire-based naturalist and patch birder, who has recently completed a degree in Natural Sciences. He has a strong interest in bird migration and has, over the last few years, started to sound-record nocturnally migrating birds from his urban garden– contributing to a garden list of 128 bird species. You can follow him on Twitter.