Marine mammals remember where their food sources are located and develop strategies to find and catch their meals as efficiently as possible.
Working with Risso's dolphins (Grampus griseus) researchers from University of Western Australia has demonstrated that the dolphins remember where their prey is, and change the depth and location of subsequent squid-seeking dives accordingly.
Like other dolphins, Risso's dolphins find prey using echolocation. They prefer to feed near coasts, but not in the shallow waters. Rather, they like the deeper offshore water where their favourite food — squid — tends to hang out most.
The scientists equipped some of the mammals with sound-and-motion recording tags to reveal where they focus their attention through their externally observable echolocation and how they fine tune search strategies in response to expected and observed prey distribution.
When they analysed the dolphins' behaviour, they noticed that the dolphins seemed to pull information about previous dives into their next.
At the start of the dives, whales adjusted their echolocation inspection ranges in ways that suggest planning to forage at a particular depth. Once entering a productive prey layer, dolphins reduced their search range comparable to the scale of patches within the layer, suggesting that they were using echolocation to select prey within the patch.
As soon as they started swimming down, the animals started echolocating at a frequency corresponding to the depth at which they encountered most squid during the dive prior. Then as they swam back to the surface for another breath, the dolphins kept up their clicking, even though they weren't hunting.
It was as if they were seeing what prey might be out there and the dolphins then adjusted their strategy on the next dive to accommodate any information they'd gathered.