Naked mole-rats never cease to amaze. They are very unusual rodents. They are almost naked, very resistant to cancer, and can live up to 30 years, in large underground colonies with a single reproducing female – the queen. Recently scientists discovered that separate colonies have their own dialects and that naked mole-rats show considerable vocal flexibility and learning.
Chatty rodents with dialects
Naked mole-rats make noise constantly and have at least 17 distinct call types. The one they use the most is the so-called “soft chirp”. Individuals use it to greet each other when they meet in a corridor.
Researchers recorded thousands of chirps from several captive colonies and analysed them using machine-learning techniques. Calls from different colonies could clearly be distinguished based on a combination of peak frequency and asymmetry in the sound, along with other sound characteristics.
Knowing your colony mates
When animals were kept individually and listened to calls recorded from different colonies, they more often responded with chirps to calls from their own colony. This does not seem to be just a result of recognising the chirps of specific individuals, but rather the colony-wide call type. When researchers created artificial sounds using the characteristics found in the recorded samples, animals responded more to sounds resembling their colony calls.
Differences in greeting calls between colonies are probably important for recognising intruders. This is crucial for assuring the cohesion and safety of the group.
Learning proper dialect
What type of call an individual makes depends on the colony in which it is raised. When orphaned pups were moved between colonies, they started using chirps characteristic of the foster group.
But not only the young can learn a new dialect and call type is actually not completely stable within a colony. When a queen dies, a period of anarchy begins, when multiple females fight to become the new queen. Chirps recorded in such a period were more variable. However, when a new queen emerged, the calls became more uniform again but differed from the calls under the previous queen.
The authors of the study concluded: “here we show that naked mole-rats signal social membership with dialect usage. Dialect features can be transmitted across generations, a surprising feat for a rodent species”.
Vocal learning is actually rare even among other mammals. It is likely, that the social complexity in naked mole-rats evolved together with their vocal complexity. It may be something that they have in common with humans.
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Photo: Von Ltshears – Eigenes Werk, Gemeinfrei, https://commons.wikimedia.org/w/index.php?curid=1568930;