Mountain goats are constrained to give birth in a short birth season synchronised with forage productivity.

Birthdate, mass and survival in mountain goat kids: effects of maternal characteristics and forage quality

Steve D. Côté and Marco Fest-Bianchet

Oecologia

Volume 127, Number 2

The other day I was discussing with my friend Ramesh, the productivity of grasslands and its impact on birth of Nilgiri tahr. The paper referred to above came in handy during the discussion.

Even though the paper lays stress on temperate environment it proved useful in our discussion. In temperate environments, early-born ungulates may enjoy a longer growth period before winter. This gives them a chance to attain a higher body mass and an increased probability of survival compared to late-born ones.

The researchers assessed the effects of maternal characteristics, forage quality and population density on kid birth date, mass and survival in a population of marked mountain goats (Oreamnos americanus) in Alberta.

The duration and timing of the birth season were similar in all years. Births were much synchronised: 80% of kids were born within 2 weeks of the first birth. Maternal age, maternal social rank and density did not affect kid birth date or mass. Kids born to pluriparous mothers were heavier during summer than kids born to primiparous mothers.

Male and female kids had similar mass and accumulated mass linearly during summer. Early-born kids were heavier than late-born kids.

Faecal crude protein (FCP) in late spring and maternal mass were positively related to kid mass. Survival to weaning appeared higher for males (90%) than for females (78%), but survival to 1 year was 65% for both sexes. FCP in late spring, density, birthdate and mass did not affect kid survival to weaning in either sex. Survival to 1 year increased with FCP in late spring for females, but not for males. Survival to 1 year was independent of birthdate for both sexes, but heavy females survived better than light ones. Multiple logistic regressions revealed a positive effect of mass on survival to 1 year when the sexes were pooled.

The researchers say their results suggest that mountain goats are constrained to give birth in a short birth season synchronised with forage productivity.