Similar NFCs

• 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.

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 alightning-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.