(The Independent – 7, August 2013) - New study shows that the
mammals have the longest social memory of any non-human species
Dolphins are able to remember one another's signature calls
for at least 20 years making it the longest memory for "faces" among
animals - perhaps even surpassing the ability of people to remember one another
from their appearances alone.
Every dolphin has a unique whistle which is used as a
signature call and stays with them unchanged throughout life. These identifying
noises are even more reliable than the facial features used by people to
recognise each other, which notoriously change over time.
Now a study has shown that when dolphins have been separated
for 20 years or more they are still able to distinguish the whistle call of a
former close companion from a host of other calls emitted by complete
strangers, scientists said.
This kind of "social memory" surpasses the
recognition abilities of elephants, primates and all other intelligent animals
that have been studied in this way, said Jason Bruck, who carried out the work
whilst studying for is PhD at the University of Chicago.
"This research shows that dolphins have the potential
for lifelong memory for each other regardless of relatedness, sex or duration
of association. This is the first study to show that social recognition can
last for at least 20 years in a nonhuman species," Dr Bruck said.
"This shows us an animal operating cognitively at a
level that's very consistent with human social memory. This is the kind of
study you can only do with captive groups where you know how long the animals
have been apart. To do a similar study in the wild could be almost
impossible," he said.
The study, published in the journal Proceedings of the Royal
Society of London B, involved collecting the recorded signature whistles of 53
different bottlenose dolphins living at six different facilities, from the
Brookfield Zoo near Chicago to Dolphin Quest in Bermuda.
The dolphins at these sites are part of a captive-breeding
programme and they have periodically spent time together going back many years,
complete with fully-verified records.
During the study, Dr Bruck would play a recording of
signature whistles of a stranger that a dolphin had never heard before. After
repeating the call many times, the dolphin would quickly show signs that it is
bored with the sound of another dolphin it had never met, he said.
Dr Bruck then introduced the call of a dolphin they had once
known, and measured its response and behaviour. "When they hear a dolphin
they know, they often quickly approach the speaker playing the recording. At
times they will hover around, whistle at it, try to get it to whistle
back," Dr Bruck said.
In one notable example, for instance, a female named Allie
living at Brookfield Zoo recognised and responded to a recorded call of female
called Bailey, now living in Bermuda, which had shared a pool with Allie 20
years and six months previously when they both lived at Dolphin Connection in
Florida Keys, he said.
Dolphins are thought to live for about 20 years on average
in the wild, although they are known to live as long as 45 years in captivity.
It is possible that they social memory for signature whistles could last their
lifetime, Dr Bruck said.
This is the longest, scientifically-tested social memory in
animals, matched only by the anecdotal reports of elephants being able to recognise
their mothers after 20 years of separation.
A study published earlier this year by researchers at the
University of St Andrews found that dolphins not only recognised each other by
their whistles but often mimic a close companion's unique whistle in an attempt
to get them to respond.
"We know they use these signatures like names, but we
don't know if the name stands for something in their minds the way a person's
name does for us. We don't know yet if the name makes a dolphin picture another
dolphin in its head," Dr Bruck said.
