Grazing sheep who perceive that they are under attack from a predator will attempt to reach the center of the flock to protect themselves from harm, new research shows. The findings support the commonly held "selfish-herd" theory, which hypothesizes that animals flock together to minimize their individual risk. The theory is widely accepted but has been subject to little experimental verification.
A team led by Andrew J. King of the Royal Veterinary College of the University of London in Hatfield, Hertfordshire, studied a flock of 46 sheep, each equipped with a backpack containing a GPS module and data recorder. In three separate experiments, the dispersed grazing sheep were rounded up by a trained Australian Kelpie dog, which the sheep perceived as a threat. The dog was outfitted with a similar backpack.
The team reported in the journal Current Biology that, in each case, the sheep started gathering when the dog was about 70 yards away from them. Each sheep did its best to get to the center of the flock, and the entire flock moved away from the dog. The animals' behavior, the team reported, could be described with a simple mathematical model and suggests that each sheep appears to be considering the position of multiple neighbors in order to move toward the center of the pack to save itself - the classic mechanism of selfish-herd behavior.
Some members of the herd appear to consistently come out better than the others in the tests, and the researchers are not sure why. They are now giving the animals physical fitness and personality tests to look for predictable patterns. The researchers also want to sort out the "rules" the sheep follow in order to move in such a remarkable and orchestrated way.
Reprinted in part from the Los Angeles Times