Common Blackbird

Given how familiar and available Common Blackbirds Turdus merula are for most of us, it is easy to forget that northern and eastern populations are migratory. If you live in central, western or southern Europe, that Blackbird flying across your garden on a winter’s morning could have come from the north coast of Norway, from a Finnish forest or from a Moscow garden.

In the black of night, Blackbirds are far less conspicuous than Redwings T iliacus and Song Thrushes T philomelos, as if their flight calls were somehow as shady as their plumage. In reality they use the same flight call at night as during the day. Probably many escape detection by sounding similar to Redwings, sometimes even to more experienced ears. With sonagrams they can be told apart quite easily, as we will show. By ear, it’s a question of critical listening and patient learning, making the most of all opportunities to learn their flight calls by day.

For a limited period each autumn, some locations in mid-latitude Europe can experience quite intense Blackbird migration. A few individuals migrate as far south as the Maghreb but the further south you go, the more difficult it becomes to tell a real migrant from a local bird active and moving around at night.

srrri calls

• high-pitched srrri with a silvery, trilled quality to it
• most calls single-note, but two-note calls common (j – m); out of 135 calls, 86 were single-note, 40 were two-note, 8 were three-note, 1 was four-note
• prominent side-bands on either side of the main frequency band; usually 2-3 bands visible in sonagrams, more at close range (d); occasionally just a single band (i)
• slow modulations, modulation rate 21 – 27 Hz (90% range; median 24 Hz; or 37 – 48 ms length for one modulation; median 42 ms; n = 135); occasionally, just a hint of superimposed fine modulations (b, e, h)
• modulations are of similar depth throughout the call (unlike European Pied Flycatcher Ficedula hypoleuca or Goldcrest Regulus regulus)
• within each modulation descending slope more prominent than ascending slope, so that weaker sidebands may look like a rapid series of descending lines (d, g)
• inflection of each note is descending, but more or less straight (n) and rising notes (g) may occur
• in multiple-note calls, slightly descending sequence overall (l)
• peak frequency for first note 6.8 kHz (±0.45 kHz; n = 135); for second note 6.5 kHz (±0.34 kHz; n = 43); for third note 6.1 kHz (±0.64 kHz; n = 8)
• frequency range for first note 3.2 – 11.8 kHz (mean min 5.3 kHz; mean max 8.9 kHz; n = 135)
• duration of first note 156 – 277 ms (90% range; median 202 ms; n = 135); second note shorter (median 174 ms; n = 42); third note usually shorter still (median 163 ms; n = 8)

Effects of recording quality

• At very close range, more bands will appear as well as weak harmonics of all bands.
• At a distance, rising parts of each modulation may disappear and the call may appear slightly shorter when weak details at the start or end fail to carry.

alarm calls

• very rarely, a srrri call is immediately followed by another call from Blackbird’s repertoire
• srrri-tuc-tuc has very short, low-pitched notes following the usual call
• srrri-sra-cha-cha-cha-chak… consists of one or more srrri notes descending through a transition into a series of notes resembling the chuckle of a Blackbird when flushed

• Redwing Turdus iliacus NFCs can sound extremely similar to Common Blackbird. While most Redwing calls only have a much finer type of modulation giving their characteristic zeeer timbre, in a significant minority of calls there is a slower secondary modulation superimposed on this, oscillating at a rate similar to a Blackbird. The differences are: 1) that Redwing typically shows fine modulations on the greater part of each large, secondary modulation, whereas Blackbird never shows more than a slight hint of fine modulation that is unlikely to be noticed unless searched for. 2) Redwing never shows well-separated sidebands, except in sonagrams using a low temporal resolution (ie, made with a ‘window size’ of around 550 samples or more). 3) Redwing almost never has two-part calls, ie, calls consisting of two notes in close succession, which are common in Blackbird. 4) Redwing’s secondary modulation is slightly but audibly slower.
• Goldcrest Regulus regulus NFCs are uncommonly heard but can be very similar to those of Common Blackbird. The differences are 1) Goldcrest is single-banded, lacking the sidebands characteristic of Common Blackbird. 2) Goldcrest has shorter notes, and often more than two per call. 3) Goldcrest shows strongly diminishing modulation size (vertically) within each note; the first modulation is by far the deepest; Blackbird shows more even modulation through each note. 4) Goldcrest is slightly higher-pitched, with most of its energy in the 7-8 kHz range.
• European Pied Flycatcher Ficedula hypoleuca zzz NFCs can appear similar to Common Blackbird NFCs with two bands but differ in several ways. 1) The median duration for one note is shorter in Pied Flycatcher: 142 ms compared to 202 ms in Blackbird. 2) Pied Flycatcher occupies a slightly lower frequency range, with a centre of gravity around 6 kHz, whereas the peak frequency in Blackbird is around 0.75 kHz higher. 3) Pied Flycatcher shows a different pattern of modulations, with deeper ones at the start of the call becoming shallower or disappearing towards the end.

alarm calls

• Song Thrush Turdus philomelos has similar chuk alarm calls, which are sometimes uttered at night. However, they show modulations on a descending frequency line, whereas Blackbird usually shows a more or less straight descending line or a shape similar to an inverted letter V, and at least one more frequency band above with the same shape.

• 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