Moms are always keeping a watchful eye on their kids. No matter the species, moms have different ways of calling their kids depending on the seriousness of the situation. We’ve all heard our moms call us by our full name when we’re in trouble!
It turns out that Atlantic bottlenose dolphin moms also have different ways of calling their calves, depending on the seriousness of the situation. The reason we know this is because our trainers and marine biologists conducted an experiment to find out.
We knew that dolphin mothers use a distress signal if a calf is in danger, but we didn’t know if they used other whistles or signals in different non-threatening situations. What we learned is that mother dolphins can fetch their calves, not only by pursuing them physically but acoustically signaling them to return.
Many folks are familiar with our swimming with dolphins programs and dolphin interaction programs. In addition to our programs and conservation efforts, we also do a lot of research.
We wanted to share our study with you in an effort to help you learn more about Atlantic bottlenose dolphins. The study we conducted demonstrates the communication between mother dolphins and their young.
Gotta Go, Mom's Calling: Atlantic Bottlenose Dolphin Mothers Use Individually Distinctive Acoustic Signals To Call Their Calves
Acoustic signals are an important aspect of a young dolphin’s life. For example, Atlantic bottlenose dolphin (Tursipos truncatus) mothers may use a distress whistle to warn a wandering infant to return. However, the maternal use of non-urgent calls to maintain proximity to a calf has not been systematically investigated. Given that some situations are more precarious than others, dolphin mothers likely use a variety of signals to communicate with their calves.
In this study, three mother dolphins were trained to produce their calves, a successful response resulting in both mother and calf jointly appearing in front of their trainer. Testing occurred when a calf was separated from its mother by a distance of at least five meters during a training session.
The mother was asked to produce her calf, a context that appeared to be non-urgent and non-threatening to both animals. Within the context, mothers spontaneously began to produce acoustic calls that resulted in their calf’s return. Although mothers were trained to produce their calves, they were not trained to do so acoustically and could have opted to physically retrieve their calf in the test situation. The mother’s spontaneous choice of an acoustic signal suggests that such signals are an important and efficient form of communication among dolphins.
In all cases, only the appropriate calf responded to its mother’s calls, even when an older sibling and other calves were in the vicinity. These results suggest that: (1) dolphin mothers use distinct calls to request a specific calf’s return, (2) other dolphins (including other calves) can distinguish such calls, and (3) non-urgent acoustic calls play an important role in offspring proximity and care.
Introduction
Dolphin mothers and calves must be able to communicate if calves are to survive.
Communication can take a number of forms, including tactile and acoustic signals.
Mothers may use whistles to maintain contact with their calves or warn a wandering calf to return.
Mothers may also physically herd and discipline their calves.
The present study focused on mother’s behaviors when a mother was asked by a trainer to produce her calf.
Method
Three adult female dolphins and their three calves dependent calves participated in the study.
- Ding (~35 year old female), mother of BB (female, dob 13 September 2011)
- Squirt (~27 year old female); mother of Lotus (female; dob 27 August 2009)
-Sarah (~25 year old female); mother of Grace (female; dob 11 July 2008)
Each adult female had previously been trained to produce their calves when requested to do so by a trainer.
Initially, each mother retrieved her calf by physically herding it. However, mothers quickly replaced the physical retrieval with an acoustic call, the result being that mothers could produce their calves without leaving the trainer.
Mothers and calves were paired together for a minimum of two minutes for each trial. The calf was then signaled to leave its station, sent to another location, or left on its own. After the calf departed and was at least 5m from the mother, the mother was asked to retrieve the calf.
Mother and calf behavior was recorded for each trail by an observer who also noted the times at which a mother was asked to recall her calf. Acoustic data were recorded with a single hydrophone (15Hz-20kHz+/-3db) that was placed within 1m of the mother. Acoustic data were analyzed using Raven.
Results
Mothers were much more likely to use energetically less costly acoustic signals than physically retrievals to acquire their calves during the test trials.
Each mother produced individually distinctive calls that incorporated the mother’s signature whistle but often also involved additional whistles and clicks
Moreover, only the correct calf responded to a mother’s call.
Conclusion
The dolphins were reinforced for producing their calves, not for the manner in which they did so. If their behavior was simply an artifact of some training scenario, the fact that they were first reinforced for physically retrieving their calves should have resulted in more frequent physical retrievals. But that was not the case.
The dolphin mothers’ use of individually distinctive calls to request a calf’s return is consistent with the notion that other dolphins can distinguish such calls and provides additional support for the notion that dolphin communication is flexible rather than fixed
