Dawn of the killer sheep

Press, 17 January 1989, Page 20

Dawn of the killer sheep

From the “Economist,” London

MR DENIS HEALEY, a former British Chancellor of the Exchequer, once quipped that being orally attacked by the mild-mannered Sir Geoffrey Howe (now Britain’s Foreign Secretary) was like being “savaged by a dead sheep.” This was unfair to sheep, though understandably so. . No creature is — apparently — so gently and exclusively vegetarian, confining its chomping to the grasses of lowland pastures and the heathers and sedges of harsher terrain. Apart from the occasional hapless aphid which ends up by chance inside a sheep after clinging too tenanciously to a succulent stem, vicious carnivorous thoughts would never enter a sheep’s woolly head. Or would they? Sheep on the Shetland island of Foula have been found biting the legs and wings off young ground-nesting birds. They have even bitten off their heads. In seven years sheep on Foula have mutilated or killed chicks of at least 680 Arctic terns and a smaller number of Arctic skuas. According to Dr Robert Furness of the University of Glasgow’s Department of Zoology, who has been studying them, it may not be only Foula’s sheep that have a carnivorous streak. Eking out their existence on tough heather and lichens, which are poor in nutrients, Foula’s sheep have probably turned in desperation to eating chicks in order to balance their diets. Something similar could well be happening wherever sheep graze on extremely poor vegetation which their farmers neglect to supplement. x

Before a crofter on Foula first caught a sheep red-handed, tern and skua chicks had been spotted with missing wings or legs. This was put down to attacks by otters or hedgehogs. But Dr Furness has seen the killer sheep in action. “I have watched sheep push a chick until it rolled over on to its back,” he says, “then bite off the leg or legs, swallow these, and continue grazing.”

On the rare occasions when a chick’s head is bitten off, the sheep chews it up thoroughly before swallowing it skull and all.

Attacked chicks had one or both wings, or one or both legs, cleanly severed. Most of them lived though the attack and the wound healed, but such injuries leave them ill-equipped for longterm survival.

Although up to 8 per cent of tern chicks were eaten by sheep, these losses were low compared with the rate of egg desertion or chick starvation. But the chickchewing sheep may have been one factor behind the decision of Arctic terns to desert one heathland colony and set up home elsewhere on Foula where sheep rarely stray. Dr Furness reckons that Foula’s sheep may be reacting to a shortage of calcium. A high rainfall leaches away what little there is in Foula’s soils.

On North' Ronaldsay — the northernmost of the Orkneys — crofters encourage sheep to feed on seaweed on the shoreline, which is a potent source of minerals. But on Foula high cliffs bar access to the shore. Another “vegetarian,” the red deer, is

sometimes known to chew on cast-off antlers in order to obtain calcium.

Sheep which eat the skeletons of tern and skua chicks are probably up to the same thing. The mystery is how they know that a limb or two keeps calcium deficiency at bay. Do they seek it out and smell the calcium, or have they learnt to eat parts of seabird chicks by accident? Most sheep lead gentler lives and specialise, for the most part, in the gentle art of herbivorpusness. But why do animals specialise at all? Would it not be a safer bet to be an omnivore and consume a varied diet of plants arid animals as a hedge against dietary shortages? The answer is that evolution has equipped different animals for their own niches in life, adapting them in order to be as efficient as possible in the habitat they usually occupy. Sheep are remarkably efficient at devouring vegetation and making the most of it. If they were omnivores, they would not be particularly good at eating anything. Still — as man has found — a little adaptability is useful when minerals are scarce.

Copyright — The “Economist”