Early growth in male and female fallow deer fawns

In this paper we present data from a long-term study on early growth and related variables in fallow deer fawns living in large enclosures. Pre-winter body mass was constantly higher and more strongly correlated to subadult body mass in males than in females. To find out the mechanism for this higher pre-winter mass in males, we analyzed the variation in pre-winter mass in relation to sex, year, mother's body mass, age and parity of mother, birth date, birth mass, growth rate, suckling behavior, and other behaviors. Birth mass was higher for male fawns, and gestation length, birth date, and weaning date did nor differ between the sexes. Consequently, both pre- and postnatal growth were faster in males than in females. No behavioral differences were found between the sexes that could explain the difference in postnatal growth. Pre-winter mass was positively related to mother's body mass. Heavy mothers gave birth earlier and to larger offspring who grew at a higher rate, independent of offspring sex. However, male fawns born to primiparous mothers had relatively lower growth than male fawns born to multiparous mothers. This was not the case for female fawns. Suckling time after the first 2 weeks was positively related to mother's body mass and growth of offspring. However no measurements of suckling behavior differed between male and female fawns. Our results, except for the effect of parity on male and female growth, indicate that selection has not acted on mothers to promote faster early growth in males.