When too much sex is exhausting
New Scientist, 10 April 1999
tough rams may get more sex, but they're victims of their own success.
They run out of sperm before the mating season is over, so their
scrawny competitors end up fathering most late-born lambs, researchers
Brian Preston of the University of Stirling and his
colleagues studied a flock of wild Soay sheep on the Scottish island of
St Kilda over three years. They observed the behaviour of more than 100
sheep during the mating season, which runs for five weeks in November
During this time, the heaviest males copulated
most. Some had sex more than ten times a day thanks to their skills at
fending off other males. But blood samples later revealed that although
big sheep fathered most offspring overall, small sheep fathered just as
many lambs as large ones in the last two weeks of mating.
lighter males were gaining in paternity toward the end of the rut,"
Preston concluded at a meeting of the Association for the Study of
Animal Behaviour in Newcastle last week. He believes this happens
because the promiscuous large sheep simply run out of sperm.