Only the male of Austral Thrush is known to sing. The song consists of phrases of whistled and screeching syllables produced at a regular tempo, typical for a Turdus. Syllables can consist of up to four notes each, but usually are single noted. The number of syllables per phrase varies considerably depending on the situation, as explained below. Lower pitched syllables tend to be whistled and loud, whereas high pitched ones are typically screeching and more faint. Song repertoire size is variable among males, and could be an indicator of the bird's age, supporting an open-ended learner condition for the species.
Each male has his own song repertoire, and the entire population shares a number of syllables. There are variations in singing behavior, depending on the arousal level of the bird:
- Slow song: a slow, short-phrased song. On average, phrases range from 3 to 8 syllables each. Performed when the male is relaxed with no competitors or females around.
- Strong song: song delivered with a faster tempo, louder voice, and more continuous singing, making it more difficult to discriminate between phrases. Performed when a rival male is near and singing, as a vocal fight.
- Soft song: a very fast and faint song, which often includes more interspecific imitations. Performed when a fertile female approaches a male in the breeding season, and are usually delivered in persecution flights.
Mimicry Austral Thrush often imitates other sympatric species with high accuracy, though detection is cumbersome (because imitations usually are very short) and requires the listener to have high expertise in the entire vocal repertoire of local bird communities. Among the species mimicked are: Dusky Tapaculo Scytalopus fuscus, Magellanic Tapaculo Scytalopus magellanicus, Ochre-flanked Tapaculo Eugralla paradoxa, Chilean Flicker Colaptes pitius, Tufted Tit-Tyrant Anairetes parulus, White-crested Elaenia Elaenia albiceps, Austral Blackbird Curaeus curaeus, Southern Lapwing Vanellus chilensis, and Plumbeous Rail Pardirallus sanguinolentus; and birds of prey such as Austral Pygmy-Owl Glaucidium nana, Chimango Caracara Milvago chimango, Variable Hawk Geranoaetus polyosoma, and White-throated Hawk Buteo albigula.
Before the breeding season starts, the male may perform a version of soft song which is very faint and fast, with very few repetitions. If given by adults, this may serve as a vocal training for the breeding season. If given by young birds it could be part of the subsong of the species. Since this song type has been recorder only with an Autonomous Recording Unit, the age of the bird who performed it remains unknown. Nevertheless, if Austral Thrush is an open-ended learner, as suggested above, the repertoire size for the recorded soft song may indicate that it was an experimented adult male.
Song Syntax Very variable, but some consistency can be observed when analyzing sonograms of the song. In some points of southern Chile, songs phrases starts with the same syllable before switching to another "start syllable" (eg. ABCD-AEFD-AEFD-EFGH-EFHI...), adding new "middle" syllables to the phrase and repeating some of them more often than others. Some of these "favorite" syllables can be thought as leitmotiv syllables, which may allow us to identify an individual. Before switching to a new start syllable, the male usually repeats the entire last phrase.
Figures 1-3 show the song syntax of the slow song given by an adult male at Lanalhue Lake, in southern Chile: ABA'B-ACDBC-ACDBC-CD...-CGHI-CGHI.
Nevertheless, this syntax structure may not be the same for all Austral Thrush populations. More research is needed in order to determine whether song syntax and repertoire size can give information about age and if they are related to mating/breeding success.
The call repertoire of the Austral Thrush reaches at least 10 signal types. The functions of some calls are unclear since they use them in several contexts, but observations about the associated behavior are given when possible.
A. Contact call: Probably the most common call of this species, the contact call can be heard all year round. It is given when the bird seems relaxed, often when foraging. An short, low-pitched, up-slurred note, presenting non-harmonic components which indicate simultaneous action of both sides of the syrinx, which contribute to its nasal timbre. Notice the striking difference of this call when compared to its equivalent call in Falkland Islands, which may have taxonomic implications. Sound recorded by Andrew Spencer: ML77307351.
B. Alarm-arousal call: Another common call, delivered apparently when the bird is exited, often when a predator is near. Much harsher than the contact call, with a rattle-bell timbre. It can be higher-pitched and louder depending on the arousal level of the bird.
C. "See" (alarm) call: The typical "see" call that many passerines use to alert about the presence of a predator, especially hawks. This is a whistled, high pitched (around 7 kHz), slightly up-slurred, pure note, with a single, faint harmonic. This signal is very difficult to locate with accuracy.
D. Breakout or fear call: A faint, low-pitched call, hard to hear from a distance. Often released when the bird is surprised by a human -and maybe other predators?- and fly away from the ground.
See ML129833861 for examples of call types A, B, C, and D.
E. Mobbing call: Often released along with call B, the mobbing call is a high pitched series of harsh, loud notes interspersed with shrill, down-slurred whistles, often modifying tempo and amplitude. This call is given when a group of thrushes mobbing a predator, especially Austral Pygmy-Owl (Glaucidium nana).
F. Long call: The long call is composed of a series -repetition- of a single polyphonic syllable: down-slurred whistle mixed with a lower-pitched screechy, rattle-like, up-slurred note. This call is unpredictable, released very few times a day, and it's function is unknown. Sometimes the male adds this call into the song syntax, specially at dusk.
G. Long call: Similar to long call F, but this version of the long call lower-pitched and only with a rattle-like timbre. Often given at dusk, after the bird ended singing and before resting.
H. "Chatter:" The chatter is a series of nasal notes interspersed with rattle-like notes. Often given when interacting -aggressively?- with other conspecific individuals.
I. Begging call: Released by juveniles when begging for food from the adults. High pitched, faint, sometimes rattle-like call, often repeated 2 or 3 times in a row.
J. Flight call: The flight call is a high-pitched call often released by flying birds, specially at high altitude (10+ meters). This call may be present in song as well.