Back in 1997, researcher Rachel Smolker and colleagues studied bottlenose dolphins (Tursiops sp.) in Shark Bay, Western Australia, and they noticed that some females often carry sponges on the tips of their rostrum.
At that time they suggested that this behaviour was the first example of tool use by dolphins. Sponges might protect the cetacean that is searching for food on the seabed from the spines and stings of animals such as stonefish and stingrays.
Now, researcher Janet Mann found out that while mothers show both their male and female calves how to use sponges, female calves seem to be more interested in this behaviour than males. ‘The daughters seem really keen to do it, they try and try, whereas the sons don’t seem to think it’s a big deal and hang out at the surface waiting for their mothers to come back up’.
Researchers are still not sure why only part of the females' population is involved in this activity and why most of the ‘spongers’ are females. They are also trying to understand if this behaviour may have evolutionary and other benefits.
Photo: Amanda C. Coakes
For more information:
Mann J., Sargeant B.L., Watson-Capps J.J., Gibson Q.A., Heithaus M.R., Connor R.C., Patterson E. 2008. Why Do Dolphins Carry Sponges? PLoS ONE 3(12): e3868. doi:10.1371/journal.pone.0003868
Smolker R.A., Richards A., Connor R., Mann J., Berggren P. 1997. Sponge-carrying by Indian Ocean bottlenose dolphins: possible tool-use by a delphinid. Ethology 103: 454–465.