Survival and behaviour of castrated Soay sheep (Ovis aries) in a feral island population on Hirta, St. Kilda, Scotland

Abstract

With 5 figures in the text)The free-living population of Soay sheep on the island of Hirta, St. Kilda, in the Outer Hebrides, has been intensively studied since 1959. The present study was initiated to throw light on the causes of the high mortality rate of adult rams in comparison to that of ewes. In 1978, 1979 and 1980, a total of 72 male lambs was castrated within a day or two of birth. The survival of these castrates has been much longer than that of the entire rams, marked as controls, and longer than that of ewes of the cohorts of the same years. The daily activity pattern of the castrates was similar to that of ewes rather than that of rams. In particular, during the rut the castrates spent most of the daylight hours grazing, in contrast to the rams who were continuously moving and involved in agonistic and sexual encounters. This study substantiates the earlier assertion that the costs in energy of reproduction are a major cause of mortality in temperate zone ungulates. The social organization of some castrates was similar to that of females in that they remained with the home-range group of ewes into which they were born, but other individuals resembled males in that these castrates clubbed together in their own groups. These patterns of behaviour persisted throughout life.

Mating system, feeding type andex situconservation effort determine life expectancy in captive ruminants

“…This is particularly interesting, as the pressure of the rut is expected to be much lower in captivity, where usually only one adult male is kept in a harem, when compared with the situation in the wild, where several males compete for the females. In one experimental study on wild-living soay sheep (Ovis aries), castrated males demonstrated a prolonged LE compared with intact males and even females [26]. Both findings together support speculations that not only an intensive intraspecific competition for females during the rut, but also reproductive physiology per se has a negative influence on male LE.…”

Seasonal changes in the rumen morphology of Himalayan tahr (Hemitragus jemlahicus) in the Two Thumb Range, South Island, New Zealand

“…Adult male ungulates typically stop feeding during the rut (e.g. Jewell 1997), and this could be expected to affect the morphology of the rumen. However, all of our winter samples were collected after the rut and most of the papilla variables that we measured in that season were slightly greater for males than for females, suggesting that the rut had relatively small and/or short-term effects on the rumen morphology of male tahr.…”

Sex differences in survival costs of reproduction in a promiscuous primate

“…Accordingly, male mating effort is often associated with lower survival (e.g., red deer, Clutton-Brock et al 1982; elephant seals, Mirounga angustirostris , Clinton and LeBoeuf 1993; Columbian ground squirrels, Spermophilus columbianus , Neuhaus and Pelletier 2001). By contrast, castration can significantly extend male lifespan (e.g., Soay sheep, Ovis aries , Jewell 1997). In ground squirrels with seasonal reproduction, male mortality is generally high during or after the mating season, whereas female mortality is high in conjunction with the birth season and lactation (Michener and Locklear 1990; Michener 1998; Neuhaus and Pelletier 2001).…”