Given that giant pandas are notoriously unprolific at reproducing, the last thing that conservationists want is for the bears’ mating capability to be compromised by human activities. In an attempt to learn more about how best to avoid disturbing pandas’ social interactions, researchers from the Zoological Society of San Diego have been investigating the range of their hearing capacity.
Hearing is a vital attribute for giant pandas, as vocal communication plays a major role in mating behavior. Unlike most other species of bear, female pandas ovulate spontaneously, and therefore become fertile at unexpected moments, leading to a sudden window of opportunity during which they can become pregnant.
At such times, they use vocalizations to announce their fertility to males, which means the ability to hear these calls and distinguish them from other environmental noises helps to determine reproductive success. However, bears in captive facilities are often surrounded by man-made noise sources, which could potentially interfere with breeding opportunities.
To ensure this does not happen, researchers set out to determine the range of frequencies at which giant pandas are able to hear, and hope to use this information to advise on which human activities should be avoided in areas close to panda habitats.
This was achieved by training pandas to respond to a tone by placing their nose on a target upon hearing it. The bears were then placed in a sound-proof chamber to ensure no other noises interfered with the experiment, while the researchers broadcast the tone at a range of different frequencies and observed the pandas’ response.
Results – which appear in the journal Global Ecology and Conservation – reveal that the functional hearing of giant pandas extends into the ultrasonic range, which refers to frequencies higher than 20 kilohertz. As such, they are able to detect a far wider range of sounds than the polar bear, the only other bear species for which hearing sensitivity data is available.
The study authors explain that this is likely to be an evolutionary trait, whereby species in forested habitats retain better high-frequency hearing than those living in flat, open spaces, since this is thought to aid survival in such environments.
However, while the pandas were found to have a wide hearing range, with an upper limit of around 70 kilohertz, the researchers discovered that sensitivity to sounds peaks at 12.5 to 14 kilohertz. As such, it is beneficial for communication between pandas to occur at these frequencies.
The presence of interfering sounds, however, could mask panda mating calls, which is why it is important for humans to limit their noise-making activities in and around panda habitats. Commenting on the findings, Ron Swaisgood of San Diego Zoo Global explained that this research makes a “significant contribution to our understanding of what may be affecting panda reproduction,” particularly in areas surrounded by human activity.