Song Thrush

Hearing Song Thrush Turdus philomelos flight calls at night may have been your first encounter with nocturnal migration. So familiar are these calls that Johann Matthäus Bechstein noted the distinctive yet unobtrusive tsip in the night sky over two centuries ago (1807), and this was how he knew that Song Thrushes were nocturnal migrants.

Song Thrush tsip calls can literally ‘fill’ October nights, resembling raindrops in sonagrams. They even sound a bit like them. Many sites can expect to record a thousand-call-night at some point during the year. When combined with high numbers of Redwings T iliacus and other species, such nights can be truly electrifying.

Song Thrush flight calls sound the same night and day, and there are many opportunities to get to know them. Typical NFCs are not difficult to identify, but some more rarely encountered variants may trip up the unwary. Given Song Thrush’s abundance, a one-in-a-thousand aberration is still likely to be far commoner than a call of some vagrant from Siberia, so we devote a special section to the more confusing, rarer variants.

Among Turdus thrushes, Song Thrush has unusually short NFCs, but the occasional hint of rapid modulation hints at a more typical-sounding ancestor. At a distance their calls seem even shorter and simpler. Few species illustrate better the way certain features of a call can degrade at shorter distances than others. At close range, fine details may appear. At greater distances, sonagrams only show a tiny trace around the peak frequency. We illustrate showing distance effects on a series given by a single migrating individual:

tsip calls

main features

• very short, very high-pitched ‘tsip’, occasionally doubled
• stereotypical shape, but many odd variants occur
• an almost vertical, rapidly descending line is always central feature
• energy concentrated at the bottom
• most start with short, weak rising line linked to main descending line (see below)
• ends with rising line, arch, level section or a handful of modulations (see below)
• mean peak frequency 7.1 kHz (±0.42 kHz; n = 186)
• mean max frequency 10 kHz (±0.67 kHz; n = 186)
• overall duration 16 – 43 ms (90% range; median 25 ms; n = 186)

variable start

• in good sonagrams, most calls show a weaker initial rising line
• linked to rest of call by narrow arch
• typically starts close to max frequency: mean 8.9 kHz (±1.36 kHz; n = 186)
• occasionally much longer line, even starting at a level lower than the rest of the call (n)
• angle less steep than main descending line
• disappears completely in more distant calls

variable ending

• all calls show sharp kink at the bottom of the main descending line, leading to:
  1) a rising line, shorter than main descending line and at a less steep angle (d), or
  2) an inverted V, usually fairly small (g, h, j), or
  3) a couple of rapid and fairly shallow modulations (i), or
  4) a short section that is nearly level (f)

doubled calls

• around 8% of calls are double (n = 186)
• 49 – 143 ms from start of first to start of second note (median 91 ms; n = 15)
• second note: lower mean max frequency, longer mean duration and more irregular shape

Effects of recording quality.

• In very clear, close range recordings, most calls show an initial rising line, starting from almost nothing. Closer calls may show faint details at the end that would not otherwise be apparent, and occasionally a lower frequency component, well below the main structure.
• With increasing distance, the initial rising line becomes shorter then disappears; the main descending line loses its upper frequencies; the ending becomes shorter then disappears entirely.

alarm calls (chuk, chuk, chik-chik-chik)

• consisting of low and quiet chuk notes in low agitation or high-pitched, strident and louder chik notes in high agitation, or the two combined
• similar to daytime alarm calls, occasionally given by nocturnal migrants, presumably in conspecific interactions, especially in nights ‘full’ of thrushes

chuk calls

• modulated rapidly descending single band
• equivalent to other thrushes’ tok or chuk calls in slight agitation
• ‘foreleg’ visible in close sonagrams
• frequency range 1.1 – 5.2 kHz (mean min 1.4 kHz; mean max 4.7 kHz; n = 6)
• duration 26 – 41 ms (90% range; median 33 ms; n = 6)

chik calls

• arched shape in two main harmonics
• upper harmonic often stronger than lower one, making call sound high-pitched
• rounded arch shape with long ‘foreleg’ and ‘hindlegs’
• typically with fine modulations on right side (‘hindleg’) of each chik
• max frequency of fundamental 3.3 – 3.9 kHz (mean 3.6 kHz; n = 5)
• duration 39 – 68 ms (90% range; median 51 ms; n = 5)

distress call (trrr-trrr-trrr-trrr-trrr…)

• high-pitched trrr-trrr-trrr-trrr-trrr…when attacked or grabbed by owl or other predator
• each trrr unit consisting of 3-5 rapidly descending ticks
• around 3-4 trrr per second
• strongest energy in 5 – 8 kHz range

tsip calls

• European Robin Erithacus rubecula has no flight call similar to this. However, during the last couple of hours of the night it is common for perched Robins to use their tik calls. They differ in being significantly lower-pitched and having a rising contour, whereas the strongest component of a Song Thrush tsip has descending pitch.
• Little Bunting Emberiza pusilla has NFCs of similar duration and slightly lower frequency range. They differ in having a rising contour, whereas the strongest component of a Song Thrush tsip has descending pitch.
• Rustic Bunting Emberiza rustica has V-shaped NFCs that are similar in frequency and duration. They can be separated by 1) having greater energy in the second half of the call, 2) lacking any rising introductory line at the start, 3) having a very subtly concave main descending slope, 4) a sharper angle at the bottom of the V, 5) often ending at a frequency higher than the start and 6) levelling off at this frequency.

alarm calls (chuk, chuk, chik-chik-chik)

• Ring Ouzel Turdus torquatus has a similar-sounding tok NFC, which differs in lacking the modulations present in Song Thrush chuk calls. Because of this, Song Thrush’s chuk sounds more liquid and Ring Ouzel’s tok more wooden. Ring Ouzel chrrk-chik-chik-chik NFCs can be even more confusingly similar (to Song Thrush’s chik-chik-chik) but differs in several ways: In Ring Ouzel the timbre is coarser; this is due to having more modulations at the start and end of each unit. Its harmonics are splayed out at the sides, creating a Christmas tree-like overall shape, whereas the harmonics in Song Thrush are more or less lined up vertically at the sides. In Song Thrush chik calls the ‘hindlegs’ are often modulated. There are further differences in rhythm and overall pattern: Ring Ouzel often has a longer unit at the start for example, and when chik calls of either species are combined with their shorter alarm call – liquid chuk in Song Thrush, typically at the start, or wooden tok in Ring Ouzel, typically at the end – separation becomes easier.
• Common Blackbird Turdus merula­ has a call similar to the chuk of Song Thrush. We know of only one case of an individual apparently in active migration giving this call, in combination with its usual NFC srrri. In Blackbird the units show a more or less straight descending line or an inverted V-shape, and usually at least one additional band, whereas Song Thrush shows clear modulations on a descending line and is less likely to show additional bands. The delivery is also typically slower in Blackbird.

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

Bechstein, J M 1807. Gemeinnützige Naturgeschichte der Vögel Deutschlands. Second edition. Leipzig.

Clement, P & Hathway, R 2000. Thrushes. London

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

Glutz von Blotzheim, U N (ed) 1988. Handbuch der Vögel Mitteleuropas. Volume 11. Wiesbaden.

Hollyer, J N 1972. Flight call of Continental Song Thrush. British Birds 65: 170.