Giant river otters are born with the gift of gab—and hums, whistles, growls, and something called a “hah!” too. Adults talk to each other and their pups using at least 22 different calls, and baby otters have another 11 sounds of their own. The findings were published in PLOS ONE last week.
Reaching lengths of a meter and a half, giant otters (Pteronura brasiliensis)—also called river wolves—are very social, chatty critters who live in highly cohesive groups consisting of a male-female reproductive pair and their offspring of varying ages. Each otter has a different role in the group, and this complex organization provides the basis for multiple long-term relationships.
To see if they have a sophisticated vocal repertoire that reflects their social structure, Christina Mumm and Mirjam Knörnschild from the University of Ulm in Germany analyzed the vocalizations of adult and newborn giant otters from five wild and three captive groups. The wild otters live at five different oxbow (or U-shaped) lakes in Peru, and the captive otters live in three separate German zoos. Their groups range in size from two to 15 individuals and cover all age classes. Using microphones connected to digital audio recorders, the duo was able to save airborne vocalizations as wave files. Meanwhile, underwater calls were recorded using a hydrophone, and in the wild, this was done while the researchers kayaked near the free-ranging otters.
Sure enough, they found that the giant otters’ social complexity is reflected in their vocal complexity. The vocal repertoire of adult giant otters comprised 22 distinct vocalization types. These were grouped in four contexts: cohesion, alarm, begging, and “other” calls such as those used for mating. Cohesion calls were used when greeting other group members, playing, and coordinating movements, and these include hums of varying lengths, barks, and whistles. Alarm calls are snorts, growls (to defend a fish), a wavering scream, and what the researchers call “hah!” (That last one was used as a warning.) Begging calls consist of ascending screams (used when stealing prey), whines, and something called a begging scream gradation. Here’s a chart of all their calls, the behavioral context, and their frequency.
The duo also found 11 structurally distinguishable vocalizations within the repertoire of newborn pups. These included: a begging-like call, contact calls, distress calls, hum-like vocalizations, whistles, and a suckling call they used while nursing. The team didn’t find an equivalent to the high whistle and the distress calls in the adults. This is the first time that vocalizations uttered in the “babbling bouts” of newborn giant otters were described. Previous studies have found that infant babbling enhances the development of the adult whist repertoire by providing ample opportunity for practice.
Here’s a great video of a family swimming and making begging, contact, and fishing calls in Lake Cocococha, Peru:
Image: Steve Wilson via Flickr CC BY 2.0
Video: PLOS Media
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