Eurasian Curlew

If ever a bird had a perfect name, then this is it. ‘Curlew’ evokes the sound of this bird’s voice, and everything about Eurasian Curlew Numenius arquata seems to curl, curve or coil, starting with the bill.

Even their repertoire as a whole is one smoothly turned gradient, where very different-sounding calls grade into one another. No species demonstrates better what is known as a ‘graded repertoire’.

Despite all the potential variety, Curlews normally use only a small part of their repertoire during nocturnal flight. Their preferred NFCs are among the simplest calls they possess. The two commonest types, separated by us because they usually sound quite different, can also grade into one another. Only a third call-type, which can be described as husky chatter, gives any real identification challenge.

The thrill of Eurasian Curlews migrating at night is not in their rarity, nor the challenge of identifying them, but in the atmospheric beauty of their calls. Allow our featured recording above to take you to a wild and special place.

low rising whistle

• long, low-pitched, slowly rising whistle
• usually a smooth rise, slightly concave (ie, rising with a slight dip in the middle)
• sometimes ends with a sudden jump up to a higher pitch, clearly audible (eg, d)
• mostly single, but can be doubled (eg, 5 doubled out of sample of 41 calls)
• doubled version composed of slightly shorter whistles (h)
• duration for first or only note 294 – 596 ms (90% range; median 408 ms; n = 41)
• frequencies from 0.9 – 2.5 kHz (mean minimum 1.5 kHz; mean maximum 2 kHz; n = 39)
• there may be a brief, barely audible ‘foreleg’ at the start (e, g, h)

Effects of recording quality

• At closer range, two clear bands nearly always show in sonagrams, a fundamental and second harmonic, sometimes more. Also, there is more likely to be a ‘foreleg’ visible.
• At a greater distance, any upper bands may disappear, as will any ‘foreleg’.

quee-quee

• two or three urgent, short, rising whistles
• normally given in social context, unlikely to be given by single individual
• an ‘escalation’ of the low rising whistle; typical examples (j, k, l) contrast strongly with that call, but intermediate calls occur (i)
• in a sample of 25 calls, seven had two notes; 18 had three notes (four or more rarely heard in very excited flocks, single-note calls may also occur)
• first note slightly shorter and usually rising slightly more than subsequent note(s)
• a ‘foreleg’, starting at a mean of 1.3 kHz, gives this call its qu-articulation (j, l)
• shape of whistled part convex, sometimes subtly (j), but most calls end with clearly audible upward inflection, clearest in the first note
• frequencies for whistled part of call 1.7 – 2.9 kHz (for first note: mean minimum 1.9 kHz; mean maximum 2.2 kHz; n = 25)

Effects of recording quality

• Closer calls may show harmonics, but not always. The qu-consonant at the start may also sound clearer, showing as a clear ‘foreleg’ in sonagrams.
• More distant calls will be lacking harmonics and may also seem to lack any ‘forelegs’.

quip

• short yelp, like a puppy
• single, double or in small clusters
• a short ‘foreleg’ followed by a little arch or peaked shape
• ‘foreleg’ sometimes slightly V-shaped
• duration of a single quip 65 – 152 ms (90% range; median 99 ms; n = 12)
• frequencies from 1 – 2 kHz (mean minimum 1.3 kHz; mean maximum 1.8 kHz; n = 12)

Effects of recording quality

• Closer calls show clearer ‘foreleg’.

husky chatter

• short, husky-sounding chatter; more often clusters of notes than single ones
• volatile: delivery speeding up and slowing down
• often interspersed with quip and other call-types
• highly variable individual notes, but many resemble husky version of ‘quip‘
• harshest notes have no definable pitch at all
• typical note harshest at the start, resolving into a more tonal ending
• note durations 62 – 217 ms (90% range; median 117 ms; n = 59)
• when discernible, pitch similar to that of quip, with most energy between 1 and 2 kHz

Effects of distance

• At close range the harshness is greater.
• At a distance the calls sound less harsh, and quieter ones become inaudible.

song

• sequence of three types of sound with hardly a break
  • 1) low, rising whistles in accelerating series, leading to…
  • 2) a fast series of ‘vibrato’ (frequency modulated) notes, then…
  • 3) several slower currrli notes, each frequency modulated and ending at a higher pitch
• exact details highly variable during nocturnal flight
• durations from 3 – 5.5 s in a sample of five

Effects of recording quality

• Beyond a certain distance, quieter first and last sounds may ‘fade in’ and ‘fade out’.

low rising whistle

• Eurasian Stone-curlew Burhinus oedicnemus has various calls at a similar pitch to Eurasian Curlew, rising sharply from a low note leading to an accented higher one. Stone-curlew rises more quickly and has a strong emphasis on the upper note than Curlew.
• Eurasian Whimbrel Numenius phaeopus has whistles that are normally shorter but when longer can strongly suggest the low rising whistle of a Curlew. Besides usually being shorter, they are 200-500 Hz higher-pitched and flatter. While the contour is rising overall in both species, in Whimbrel it is usually convex-shaped, leveling out or dropping towards the end, while Curlew has concave-shaped calls, rising more noticeably towards the end.

quee-quee

• Eurasian Whimbrel Numenius phaeopus has short whistles at a similar pitch that, when doubled, can resemble the quee-quee of a Curlew. However, the calls are quieter and the notes are usually convex-shaped, ending with an even or slightly falling pitch, whereas in Curlew the notes are concave, ending on a slightly rising pitch.
• Terek Sandpiper Xenus cinereus also has flight calls with a similar number of notes, each of which rises in pitch. However, the delivery is faster, the individual notes rise more markedly in pitch, and the call as a whole is around 0.5 kHz higher than in Curlew.

husky chatter

• Eurasian Whimbrel Numenius phaeopus has very similar husky chatter and separation can be challenging. In most cases, Whimbrel will have some pi-pi-pi-pi-pi-pi calls making identification easier. In their absence, listen whether the notes resemble husky versions of quip notes (Curlew) or short whistles (Whimbrel). Whimbrel’s husky chatter has its main energy concentrated at a higher frequency, between 1.8 and 2.3 kHz with only a weak signal below this, whereas Curlew has significant energy down to around 1 kHz. The median duration of notes in Whimbrel is marginally longer, and the tonal forms emerging from the harshness often appear slightly flatter in shape, but there is a great deal of overlap.
• Bar-tailed Godwit Limosa lapponica also has similar-sounding husky chatter, but this is comprised of shorter units, and with more separation between the notes. Although highly variable, the median note-length in Bar-tailed Godwit is only three quarters than of Curlew’s. The tonal sounds emerging from the chatter are more nasal sounding in the godwit, due to a marked harmonic structure; indeed, the whole call is spread across a much broader frequency range.

• anywhere: over towns, forests, deserts, offshore
• nocturnal and diurnal: uses same flight calls day and night
• can be expected at any hour

Eurasian Curlew has a large repertoire of calls, in which many variations and intermediate call types are possible. Although some birds in the recordings above were probably not migrating, the calls described are those that we know to be given by nocturnal migrants. However, Curlews that are not in migration mode can certainly produce additional types of calls while flying at night, especially when nesting. Bear this in mind if you are trying to record nocturnal migration in areas where Curlews are permanently or temporarily in residence.