Good
flocking behavior is the herd animal’s answer to the predator out there,
whether it is wildebeests and a lion, or homeowners and a banker. Sticking
together won’t fight off the threat, but you have a better chance of being
available for appointments tomorrow.
King
et al in the current issue of Current
Biology tried to quantify good flocking behavior using an unsuspecting group of
46 sheep with an Australian sheep dog standing in for the big bad wolf (1,2).
This was going to be a set of quantitative experiments so each sheep was fitted
with a gps system so that its precise position could be plotted as a function
of time. The sheep dog was also fitted up with a gps system so any sneaking
moves would be fully recorded.
The
result was that as the dog appeared in its role of the villain, the individual
sheep made haste to find the center of the flock. Of course, each sheep could
not be at the center simultaneously, so there was a deal of milling around as
they showed good flocking behavior with the idea that inside the group meant
that you were less likely to feel sharp teeth than if you were outside.
With
eager mathematicians amongst the observers, and a plethora of numerical data
showing sheep coordinates as a function of time, meant that the apparent chaos
of such flocking behavior could be reduced to the simplicity of a first order
differential equation. This wonder of simplicity expresses the rate that the
cohesion of the flock changes with time once the dog gets within a critical
distance.
With
these sheep and this Australian with gnashing teeth, 60 meters was felt to be
close enough to move into good flocking behavior. By the third trial, the sheep
were pretty close together before the dog appeared. I guess that they had a suspicion that it
hadn’t left for the Heathrow to Sydney flight.
- http://www.cell.com/current-biology/fulltext/S0960-9822(12)00529-5
- http://www.bbc.co.uk/news/science-environment-18959633
