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A team of experts has discovered that giraffes communicate at night by humming. Previously, it was believed that they are taciturn animals, which rely solely on visual cues, but it appears they do make distinguishable vocalizations when interacting with one another.
Scientists from the University of Vienna and Berlin Tierpark in Germany analyzed audio data collected from giraffes (Giraffa camelopardalis). More than 947 hours of sounds made by the long-necked animals were recorded throughout a period of 8 years, in 3 European zoos from Berlin, Copenhagen and Vienna.
Research focused especially on identifying tonal, infrasonic and sustained vocalizations, by analyzing sounds produced by giraffes during day and night.
The study, published on September 9, in the BioMed Central, contradicts the previously held belief that, because of they way their body is built, giraffes cannot generate vocalizations. Although they were known to have a well-developed larynx, it was thought they could only produce occasional grunts, bursts or snorts.
The commonly shared view was that airflow could not possibly pass through their 13-foot long trachea and vibrate the vocal cords. Some experts had also hypothesized that giraffes may produce low-frequency, infrasonic sounds, just like elephants do, but no superior vocal communication.
However, the research team identified 65 “harmonic, sustained and frequency-modulated ‘humming’ vocalizations during night recordings”. This was achieved by establishing a set of acoustic parameters, and visually examining “spectral and temporal components” of each sound produced by the animals.
Experts concluded that the vocalizations are not infrasonic, as previously thought. The average fundamental frequency of these rich, deep sounds was of around 92 Hz, which is still audible for humans. The vocalizations lasted between 0.41 seconds and 4.17 seconds.
Moreover, it was established that these continuous acoustic signals may function as a language, allowing animals to communicate their intentions. There were no video recordings throughout the night, to determine a definite link between the sounds and certain actions or responses. During the day, the animals communicate visually, so as not to attract predators.
Behavioral research has shown giraffes are organized in a “fission-fusion social system”, just like spotted hyenas, chimpanzees or African buffaloes. Such species normally associate in herds, which reflect their affiliation and attachment to one another. They also interact by employing complex vocalizations, that allow them to mark their presence and bond with others.
As a result, researchers had long suspected that giraffes may also have similarly sophisticated ways of expressing themselves and exchanging information, but this is the first time a study has proved this theory. Now, experts are investigating these “humming” vocalizations to see to what they might transmit and what relevance they may have to the animals’ behavior.
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