A group of bottlenose dolphins in Shark Bay, Western Australia, use a clever trick to access prey on the sea floor – they cover their beaks with marine sponges to protect themselves from sharp rocks as they search for food. 30 years after the behaviour was first reported, scientists have now found that individuals improve with practice, peaking just when it matters most.
In 1984 it was first reported that one group of bottlenose dolphins in Australia was behaving rather strangely. The dolphins were frequently observed collecting sponges from the bottom of the sea floor and carrying them about on their beak. In 2011, researchers at Georgetown University, Washington, found a possible explanation – using sponges enables females to access prey that would otherwise be off the menu. The sponges protect the dolphins’ delicate beaks, allowing them to forage for prey near the rocky sea floor and access food that they would otherwise be unable to reach without a nasty graze.
Tool Efficiency Peaks with Reproduction in Bottlenose Dolphins
Eric Patterson and colleagues from Georgetown University, Washington, found that for female ‘spongers’, a lifetime of practice culminated with peak performance during middle age. At 25, dolphins spent half as much time acquiring a sponge, and travelled up to 15m further with each one, compared to a 5-year old juvenile. Patterson’s 23-year observational study showed that the dolphins first learn to improve their sponge-collection technique, and make improvements in balancing the sponge on their beak later in adulthood.
Because the sponge-tools offer dolphins access to an additional source of prey, it may be especially crucial for expectant mothers. The researchers showed that female reproduction also peaks in middle age, suggesting that practicing sponge-use during early life may pay dividends when it is time to breed. The paper adds to our understanding of this complex, learned behaviour by showing that individuals can improve with age. Further, by showing how the behaviour relates to reproduction, this new study highlights just how important this innovation may be to the female dolphins of Shark Bay.
Want to Know More?
- Patterson, Krzyszczyka and Mann (2015) Age-specific foraging performance and reproduction in tool-using wild bottlenose dolphinsBehavioral Ecology
- Patterson and Mann (2011) The Ecological Conditions That Favor Tool Use and Innovation in Wild Bottlenose Dolphins (Tursiops sp.)PLOS ONE
- Mann et al (2008) Why Do Dolphins Carry Sponges?PLOS ONE