Suckling behavior in goitered gazelle: do females invest more in twins or singletons?

The mother-offspring social unit is a universal feature in the social life of all mammals and nursing is the most direct and vital component of maternal investment in young. Living in diverse environments, various ungulate species have different strategies for rearing offspring, from bearing a single, relatively large newborn and supplying only limited amounts of milk, to bearing several relatively small newborns with intensive post-partum lactation. In this paper, we consider the rearing strategy of goitered gazelle with a focus on suckling behavior, which, until now, has never been a subject of special investigation. Adult females of this species in their reproductive prime typically bear twins when environmental conditions are favorable, but the proportion of singletons increases when conditions are unfavorable. We expected that in goitered gazelles suckling intensity would be maximal during the first weeks after birth, and then decrease with the growth of the young; we also expected that twins would demand more energy, but receive significantly less maternal investment per young than singletons. We found that, indeed, suckling behavior had similar dynamics as typical of all bovid species, but our expectation for less maternal investment in twins vs. singletons was wrong. In reality, female goitered gazelles suckled twins significantly more intensively and terminated suckling less often compared to singletons. We concluded that in favorable situations females of high quality have the ability to show significantly more maternal investment in each twin, while singletons are typically born to weaker females. This ability of females to produce mostly twins allows goitered gazelles to take advantage of any favorable opportunity to quickly increase their population in an environment with unpredictable and abrupt yearly changes typical of the arid regions of Central Asia.