It can be difficult to make sense of the birds we hear at night. Methods include comparing calls with those from the daytime, recordings from our own collections and archives such as xeno-canto. We consult collections of daytime flight calls such as Out of the blue or Birds in flight, and articles on nocturnal flight calls on websites like this or nocmig.com. Only Eastern North America has a comprehensive nocmig guide, Flight calls of Migratory Birds (Evans & O’Brien 2002).
This guide focuses on nocturnal flight calls in Europe. When sitting outside and listening live, it can help with carefully chosen examples, descriptions of calls, and information on where and when you are most likely to hear a certain species. For the analysis of your sound-recording, it explains how to identify calls via sonagrams (spectrograms) and the measurements that can be obtained from them. If you are unsure where, when and how to record and what to log, there is A Protocol For Standardised Nocturnal Flight Call Monitoring, which gives further advice for obtaining nocmig data.
We have selected 50 nocturnal migrants likely to be recorded giving flight calls during nocmig in western and central Europe. We do not include wildfowl, as their calls are the same day and night, and there are plenty recordings available elsewhere (for Common Scoter see here).
Each of the 50 species’ accounts starts with a recording that reflects a favourable listening experience, often including calls at a range of distances, to give a first impression of how the species may sound. If you only listen to one example per species, listen to this one. We include a representative sonagram at a scale that we would recommend using (typically 4 seconds to a line and frequencies up to 10 kHz). We will show a longer stretch if appropriate. There is a scale bar at the bottom left so you can compare this sonagrams scale to that of the more detailed sonagrams in the identification section below.
We include information about the peculiarities of this species’ migratory behaviour and noctural flight calls (NFCs), for example, whether they differ from daytime calls, how many types, and how we came to know them. If the species uses a different flight call at night or has no diurnal flight call, we will present an example to show how, during the day, it does use calls similar to the NFC but in other contexts.