Bats obey 'traffic rules' when trawling for food

Foraging bats obey their own set of 'traffic rules', chasing, turning and avoiding collisions at high speed according to new research publishing in PLOS Computational Biology.

Dr Marc Holderied and colleagues from the University of Bristol studied pairs of Daubenton's bats (Myotis daubentonii) foraging low over water for stranded insects in Somerset, UK.

He said: "Collective movements of flocking birds or shoaling fish are amongst the most fascinating natural phenomena. Everyone has experienced the challenges of walking through a moving crowd, however, what information individuals use for movement coordination is very difficult to know - except in the case of echolocating bats."

These flying mammals discern their surroundings by emitting loud and high-pitched biosonar calls and listening for the returning echoes. Bat biosonar imaging is much sparser in information than vision, so Dr Holderied was able to accurately measure the biosonar calls of the interacting bats and calculate what each of the individuals perceived.

The results indicated that bats obey their own intriguing set of 'traffic rules': they chase each other, perform tandem turns and even slow down to avoid collisions.

The authors modelled the bats' biosonar view of their surroundings during these interactions and discovered that the bats swap leader-follower roles. The bats perform chases or coordinated manoeuvres by copying the heading that their leader was using up to 500 milliseconds earlier. (500ms is almost as fast as the blink of a human eye which has been measured at 300-400ms.)

Dr Marc Holderied commented: "The bats seem to have adopted a simple trick: once another individual is close enough for your biosonar to pick up its echo, copy this individual's flight direction within four to five of your own wingbeats."

Dr Luca Giuggioli said: "Quantifying the movement decisions that bats adopt to forage has implications well beyond animal ecology. By employing movement strategies that nature has optimized over millions of years, engineers may be able to improve the efficiency of search and rescue missions, monitoring tasks, and surveillance operations in the emerging market of flying drones and autonomous moving vehicles."

Source: PLOS