Black-crowned Night Heron

Black-crowned Night Heron Nycticorax nycticorax is the very archetype of a nocturnal migrant. It even has the word ‘night’ in its English and scientific names. Its name in Dutch is ‘Kwak’ and it has similar names in many other languages, imitating the sound of its NFC.

The nocturnal activity and the calls Night Herons use at night have been well known for centuries. In fact, Naumann provided a description of its eponymous qwar, rich in detail, as early as 1838. He also pointed out that the ‘corax’ in its scientific name was due to the raven-like timbre of its calls and not due to any similarity of its posture to a crouched raven or crow (Naumann 1838).

Night Herons use only one type of flight call at night. Once learned, it is fairly distinctive, although sometimes anthropogenic noises, a very distant Grey Heron Ardea cinerea or Eurasian Bittern Botaurus stellaris can sound similar. However, the specific timbre of Night Heron’s qwar should always be audible.

The chances of hearing a Night Heron one night at your home – wherever it is – are not bad. Why? The grenade effect! The young Night Herons start spreading out in all directions immediately after breeding time, more than other species (Berthold 1993). Wherever you are, whether near their colonies or way north of their breeding range, in a forest or in a city, give it a go – you may hear one.

qwar calls

• medium pitch, roughly as Grey Heron Ardea cinerea
• timbre not particularly nasal, but more baby-voice-like: press the rear part of your tongue against your upper teeth and say “wha” in a baby voice
• sounds frog-like, sometimes more duck-like
• mean peak frequency 1.6 kHz (±0.13 kHz; n = 61)
• frequency range 0.8 – 2.2 kHz (mean min 1.2 kHz; mean max 1.8 kHz; n = 61)
• shape in sonagrams shows an arch or line with major part of the call rising in frequency (makes it sound questioning)
• frequency arch usually starts lower in frequency than it ends; ie, minimum frequency located at beginning of call
• arch often with one or more kinks in the course of the frequency band; a diagnostic feature when present
• duration 121 – 233 ms (90% range; median 163 ms; n = 61)
• mnemonic: it rhymes with “what?”

Effects of recording quality

• Calls at very close range can have additional frequency bands above and below or show more croakiness, which blurs the sonagram.
• Distant qwar calls may show only a faint single frequency band in an apparently straight line, which otherwise would show rising parts and a kink in the frequency band.

• Eurasian Bittern Botaurus stellaris has a lower pitched NFC, which otherwise strongly reminds of Night Heron’s qwar when pitch is difficult to assess. A good reminder is, that Eurasian Bittern’s grouw sounds descending, whereas Night Heron’s qwar sounds rising, as if asking a question. Bittern NFCs are also longer.
• Grey Heron Ardea cinerea has a similar general pitch but its rrank is otherwise different in timbre and shape of the call. Grey’s rrank has every so often a strident or shrill timbre. It shows (depending on quality of the recording) a broad bandwidth without one clear main frequency band (often it shows two instead), whereas Night Heron has often a clear main frequency band and additionally may show a prominent rising part and kinks in the course of the frequency.
• Little Egret Egretta garzetta is a potential confusion risk as its NFC argh, similarly pitched, is not well-known among birders. It sounds not prominently rising overall but rather gurgling and invariably croaky; sometimes even slightly descending with a hint of the diphthong ‘aʊ’. Shape appears as a diffuse block or arch and may show diagnostic frequency bands in zig-zag lines, resulting from the gurgling, slightly shivering timbre of its call.
• Little Bittern Ixobrychus minutus is remotely similar but its NFC ker is distinctly higher-pitched (mean peak frequency is 2.2 kHz) and sounds overall slightly descending, like a miniature Eurasian Bittern.

• anywhere: over towns, forests, mountains, offshore; but more likely near rivers or lakes
• mainly nocturnal: but may start or finish migration in twilight
• typically in the middle of the night: but recorded any time between dusk and dawn

Berthold, P 1993. Bird migration: A general survey. Oxford.

Naumann, J F 1838. Naturgeschichte der Vögel Deutschlands. Volume 9. Leipzig.