The Animal Kingdom team has devised eight broad categories of elephant calls, based on how the sounds can be grouped acoustically (please see the image caption for links to audio files of these sounds).
"We have the technology to compare all the different [noises] and match them to individuals," said Kirsten Leong, an Animal Kingdom researcher. "We are looking at every call they make and look at whether the repertoire can be broken down acoustically and not only according to what the elephants are doing."
"Eighty to 90 percent of our recordings are of rumbles," Leong said. "We find the elephants also use them when they are interacting at very close distances."
Through regular blood tests to monitor hormone levels, the researchers have been trying to track if vocalizations change over the elephant's reproductive cycle. "We are looking at how vocalizations might be used as a signal to the male, and possibly other females, to advertise their fertility," said Savage.
In the wild, elephants generally live in groups segregated by gender. Adult male elephants are generally solitary or associate with other bulls in loose associations while females live in families. During sexually active periods, known as musth, males spend much of their time searching for mates. Adult males only enter female herds temporarily for mating.
"Given that males and female herds are separated by several miles, how do males know when females are in estrus? We are looking at how female elephants signal to males their impending fertility," Savage said.
Bulls Always Looking for Mates
Researchers in Africa have observed that bulls are always looking for mates, using smell and hearing to seek out particularly females in estrus.
"In a 16-week cycle, females are fertile for only two or three days, a maximum of four times each year," Leong said. "Most of the time in the wild elephants do become pregnantso realistically between pregnancies it is generally four or five years before they will ovulate again. How do the elephants find a mate when the window of opportunity is so small? It is believed that females must be advertising with vocalizations, and that that males are hearing this from far away."
Vocalization with infrasonic components is how elephants make long-distance calls. The very low-frequency sound that humans cannot hear can be heard by other elephants across great distanceshumans in proximity to the elephants hear the upper frequencies of these powerful calls. Researchers in Africa have found evidence that elephants can identify up to a hundred individual voices from more than a mile awayand there are suggestions that elephants might be able to communicate over distances upwards of 20 miles (32 kilometers) by making the ground vibrate.
The ability to communicate over long distances could mean that males can monitor different female herds at the same time, listening in to groups near and far and moving in whenever they hear a female that sounds like she is ready for mating.
"We've monitored changes in vocalizations when a female is getting ready to ovulate," Leong said. "Although many of the vocalizations appear to be related to changes in female-to-female interactions, males could easily gain information by eavesdropping on these vocal exchanges from far away."
Researchers at the Animal Kingdom have noticed that when a male joins the female herd there is no special vocalization within the group. Instead, the male shows more than usual interest in the females by performing a lot of genital inspections with his trunk. "It turns out that when the male is right there they don't talk about it," Leong said.
Observations in the wild have indicated that females may show indifference to a young male but become audibly excited when a musth male shows up, often rumbling in a group in behavior known as the "female chorus."
The Animal Kingdom project is small in that it is focused on a tiny herd of elephants in a relatively confined space (although by zoo standards their enclosure is impressivea "savanna" of many acres landscaped to approximate grasslands, forests, rivers, and hills). But the Disney scientists believe they have some unique advantages in that they can pinpoint the vocalization of not only each individual as it emits the sound but also monitor any response and ensuing "conversation."
A zoo project like the Animal Kingdom's provides a comparison of vocalization of animals in captivity with that of elephants in the wild. Knowledge gained from elephants born and living in captivity can help those remaining in the wildwhile the work in Africa allows zookeepers to gain a better understanding for breeding and caring of animals in their care.
"We're using our elephants to do what we can to protect the elephants in the wild," said Savage. "It's not just the research, of course, but how the millions of visitors to Disney's Animal Kingdom react to them and our work with them. Awareness of these great animals and how they communicate helps people appreciate them and understand why it is important to protect them in the wild."
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