Ring Ouzel

Nocturnal flight calls of Ring Ouzel Turdus torquatus are never common but always striking. One NFC is enough to awaken any half-asleep listener with a jolt. Night totals rarely exceed a handful, but many of us are in with a chance. Ring Ouzels breed in remote, mountainous habitats from arctic Scandinavia to southern Europe and winter in the Mediterranean region, meaning that almost anywhere in Europe one could pass overhead at night. But in practice, a complex migration strategy leads to migrants being commoner in spring in the west (Cramp 1988).

Sagres in Portugal is a good location for nocturnal passage, with 75 Ring Ouzels recorded between 2017 and 2020. Most individuals only gave a single call within range of the microphones, sometimes a second after a longish gap, occasionally a third. Four or more calls during a flypast are rare. We have experienced this only on one exceptional night on Menorca, Spain, when over ten individuals passed. It seems likely that the longer call sequences were actually from multiple individuals.

The most common NFC, a raucous chrrk-chik-chik-chik, is a call that Ring Ouzels also use commonly by day on migration and in flight. Every so often they combine this call with another from their repertoire, for example, the series chrrk-chik-chik-chik ends with a deep and knocking tok. The tok units can also be used as NFC separately, on their own. A third NFC is a usually dry-sounding prrrt or prrrt-prrt. A similar note sometimes replaces the first unit of a chrrk-chik-chik-chik. Combined calls lead to the overall perception that NFCs of Ring Ouzels are extremely varied and complex.

We often struggled to assign a recording to any specific call type,. It seems that occasionally, Ring Ouzel NFCs will not fit neatly into our categories. This is especially true for the prrrt-prrt where we found highly diverse examples, presumably with varying levels of excitement. These included some that we have never heard being used as a flight call in daytime (for example, o).

chrrk-chik-chik-chik

• a series of 2-6 units of similar pitch (median 4 units; n = 47)
• units can be transcribed as chrrk, chrek or chik; amount of ‘r’ depends on modulations; sometimes the last unit is a lower-pitched tok
• units have a ‘Christmas tree’ outline with a tall arch, an M-shaped structure or a few high modulations in the centre; on the sides, a series of harmonics show as gently sloping ‘branches’
• first unit often stressed, longer, or replaced by a modulated prrrt
• modulations, when present, typically on first units of call only
• first unit often longer, 57 – 187 ms (90% range; median 98 ms; n = 43)
• last unit shorter, 24 – 110 ms (90% range; median 57 ms; n = 42)
• total call duration 285 – 686 ms (90% range; median 457 ms; n = 47)

Effects of recording quality

• At close range, an even wider frequency range will reach the listener.
• At distance, the frequency range will seem slightly narrower, and any final tok may escape attention. In sonagrams the ‘Christmas tree’ pattern may be hardly recognisable.

toktoktoktok

• from three to seven identical tok units (median 5; n = 8)
• untidy, ‘splattered’ rhythmic pattern; sometimes more than one series in quick succession (j), or a cluster followed by a single tok (i)
• individual tok very short and a little ‘wooden’-sounding
• when magnified in sonagrams, shows a vertical concentration of energy on the left side and a series of many downward-sloping bands on the right
• first tok has duration 29 – 44 ms (90% range; median 34 ms; n = 8)

Effects of recording quality

• At close range, an even wider frequency range will reach the listener.
• At distance, the frequency range will seem slightly narrower and measurements of duration will give slightly shorter values: the weakest final milliseconds will be lost.

prrrt-prrt

• from one to three prrrt units (median 2; n = 15); longest of the unit-types
• first unit 81 – 248 ms (90% range; median 186 ms; n = 15)
• last unit 33 – 150 ms (90% range; median 99 ms; n = 15)
• pitch usually rising both within each note and from start to end of call
• deep modulations starting from the bottom, often becoming shallower as the pitch of the call rises

Effects of recording quality

• At a distance the lowest parts of the call the will be lost and for example the start frequency will not be possible to measure accurately.

chrrk-chik-chik-chik

• Song Thrush Turdus philomelos­ has a similar call-type, not its main NFC but sometimes recorded in the context of nocturnal migration. It can easily be confused with Ring Ouzel. In Song Thrush an arch is also the main structure of each unit, but these are simpler with at most some very shallow modulations. The start and finish of each unit is ‘cleaner’ with the ‘forelegs’ and ‘hindlegs’ lined up vertically, not splayed out like the sides of a Christmas tree as in Ring Ouzel. Another telling difference is that Song Thrush puts much more energy into the second harmonic, whereas Ring Ouzel focusses its energy much more in the fundamental.
• Fieldfare Turdus pilaris is not a serious confusion risk except when it comes to a minority of Ring Ouzel calls with more than the usual number of units, which can resemble Fieldfare’s main NFC. Fieldfare has units that are usually slightly longer, and contain more ‘noise’, showing as cloudy smudging in sonagrams. In addition, many layers of rising bands at the start of each unit are more prominent and have longer duration than any descending bands visible at the end. To use a visual analogy, Fieldfare units are like slightly ragged standing up feathers with the broader web on the left and the shaft towards the right, whereas in Ring Ouzel the broader web is on the right and the shaft sits close to the left side.

toktoktoktok

• Common Blackbird Turdus merula has a similar call that may sometimes be heard while listening to nocturnal migration, but mainly from local residents becoming active while it is still dark. We know of only one case of an individual apparently in active migration giving this call, in combination with its usual NFC. In Blackbird the units are much less abrupt and sharp-sounding, ie with longer duration, and the delivery is slower. There are no ‘machine-gun bursts’ as in Ring Ouzel.
• Redwing Turdus iliacus also has a rattle call occasionally used at night. It is easy to separate from Ring Ouzel since each unit of the rattle is in itself subdivided into two or more tk units very close together, each of which has a
  lightning-like shape. The call as a whole sounds like trt-trt-trt-trt.

prrrt-prrt

• Common Starling Sturnus vulgaris and Spotless Starling S unicolor have similar flight calls that are rarely heard at night. They differ from Ring Ouzel in being, on average, longer and more evenly modulated as well as sounding lower-pitched. The timbre is more ’rounded’, with a greater homogeneity giving a less aggressive tone. In addition, starling flight calls typically consist of single units, not two units in rapid succession as is typical for Ring Ouzel.
• Mistle Thrush Turdus viscivorus can be a confusion risk with the driest variants of Ring Ouzel prrrt calls. Mistle Thrush’s NFC has even shorter single elements, never connected to a modulated frequency line. The single elements have the shape of an upside-down ‘V’ and are often spaced unevenly within the rattle. Ring Ouzel’s call has elements with an upward line most prominent ‘/’ and are spaced more evenly. But as a matter of fact, we have not yet recorded these very dry sounding variants of the Ring Ouzel NFC prrrt at night.

• anywhere: over towns, forests, mountains, offshore
• nocturnal and diurnal: uses same flight calls day and night, although prrrt calls seem to differ slightly at night
• can be expected at any hour: a bias of activity towards second half of night

Cramp, S (ed) 1988. The birds of the Western Palearctic. Volume 5. Oxford.