"Aerial Disturbance" Roar Spectrogram
No aerial predation attempts by raptors have ever been observed, although these sifakas sometimes stare skyward and emit these high amplitude broadband "aerial disturbance" roars in the presence of the large Madagascar buzzard (Buteo barchypterus), which does not eat lemurs, and other small birds.
This high amplitude, tonal, and extremely frequency modulated vocalization can be considered the silky sifaka submissive signal. It is typically only emitted after an individual receives aggression. It exhibits greater frequency modulation than an call within their repertoire.
These Tonal, harmonic, and moderately frequency modulated calls can be considered the "lost call" of this species. Typically they are emitted when individuals become spatially separated from the group. Uon hearing these calls, often group members will immediately respond with "Zzuss!" alarm vocalizations. Subharmonics are occasionally apparent.
These low amplitude, tonal, and very low frequency “contact calls are one of the most common silky sifaka vocalizations. They are often emitted during and just prior to group movement, while also being emitted in a variety of affiliative and resting contexts. Oddly, as in the case above, a fundamental frequency often seems to be absent; this may be an example of an anti-resonance in which properties of the vocal tract filter out the frequencies containing the fundamental.
Similar to hums, but shorter in duration and more frequency modulated, these low amplitude and low frequency, tonal “ contact calls” are emitted during a variety of affilliative and movement contexts. Mums are amongst the most commonly produced vocalizations emitted by silky sifakas.
These pulses of broad-band noise sound a bit like a cat’s purr, hence the name. They are low-amplitude and fairly uncommon. Oddly, most purrs are emitted when a single adult approaches a human observer within a few meters, stares directly at the observer and emits these purrs. Silky sifaka purr calls may function as a low-level threat vocalization.
Zzuss vocalizations can be considered a general purpose alarm call. These high-amplitude calls contain clear harmonic components in combination with substantial broadband noise. Zzuss are mainly emitted to terrestrial disturbances, in response to "howl" calls by other group members, and after receiving aggression. Sex and individual difference have been documented in the acoustic structure of the silky sifaka zzuss call.