The Sheep Year

The lives of sheep are dictated by the seasons. For much of the year, males live in bachelor groups occupying particular home ranges and feeding hard. During the spring and early summer they grow a new horn increment and put on condition. As Autumn approaches, they engage in increasing levels of head-butting and fighting, and by the rut in November they are roving around the island, assessing individual females for oestrus status. If a male finds an oestrous female, he will try to defend her for several hours and mate with her repeatedly. However, only large, mature males, with big horns can defend a female for long, and younger, smaller males and those with scurred horns (small misshapen horns, see Meet the Sheep) constantly search for oestrous females, chase them around and get quick matings if they can.

By early December, the rut is over, and the following four months are the toughest of the year for Soay sheep, as the food supply diminishes and climatic conditions are at their harshest. Most natural deaths occur between February and April, with lambs of the previous year, and males (who enter the winter in poor condition after rutting) most likely to die.

In April, the ewes give birth to lambs- most have a single lamb, but between 2% and 23% (varying across years) have twins. The first few hours and days of life are a perilous time, for if either the lamb or the ewe is too weak, or the weather too foul, the lamb may die. If all is well, the lambs grow at about 100g per day, and by August they have reached about half their mothers' size and are being weaned. Since plant growing conditions are generally fine over the summer, most ewes recover condition sufficiently to conceive in the following rut.