Maternal Tactics for Preventing Predation of Newborn Fawns
The time immediately after birth, known as the postpartum period, is a very risky time for ungulate infants. They are small, weak, and unable to run and are thus easy prey for predators. Once a gazelle is born, the fawn and its mother enter a race against the clock to get the fawn hidden before a predator detects and kills it. For this study, I observed eleven mother-fawn pairs during the postpartum period and noted the habitat type (short or tall grass) and social context (in a group or isolated) in which parturition occurred. I measured how long it took for the fawn to either move away from the birth site and begin hiding, or be killed by a predator. I also recorded any disturbances to the mother-fawn pair by other non-predator animals.
In my study, six of the eleven fawns were encountered by predators within an hour of birth and all but one of these were killed. I found that there are two effective tactics mothers can use to improve their fawn’s probability of surviving the postpartum period:
- They can leave their social group and give birth alone in an area with lots of cover (tall grass), or
- They can remain in their social group and give birth in their normally-preferred short grass habitat.
The first strategy reduces the duration of the postpartum period by reducing the disturbance of the mother-fawn pair. That is, without conspecifics around to interrupt the mother and fawn, the fawn is able to stand, walk, and hide sooner. However, this strategy increases the detectability of fawn because a lone female in tall grass is a very strong signal to predators that there is a fawn nearby.
The second strategy reduces the detectability of the fawn because the mother and fawn are less conspicuous when they are in a group of other gazelle. However, this strategy increases the duration of the postpartum period because these other gazelle are attracted to and displace the mother from the fawn, which slows the fawn’s behavioral development.
Fawns whose mother used one of these strategies had about a 60% chance of surviving until hiding. In contrast, the few females who did not use one of these strategies, either giving birth alone in short grass or in a group in tall grass, all lost their fawns within the first hour of life.
Warthog Predation
In the course of this study, I observed several instances of warthogs attacking and killing newborn gazelle, a behavior that had not been previously documented in the literature. The window of opportunity for warthog predation seems to be pretty limited: to kill the gazelle, the warthog first has to knock it over and hold it down with a hoof. Once they are an hour or two old, gazelles are able to recover from being knocked over pretty quickly, and thus avoid being held down and killed. Warthogs were very numerous at my field site, so the encounter rate between warthogs and gazelle neonates may have been unusually high, which is might explain why I observed this behavior but others have not. Interestingly, gazelle mothers do not exhibit antipredator behavior in response to warthogs near their young, providing further evidence that this is a rare or emerging predatory behavior.
Publications:
Roberts BA and Rubenstein DI. 2014. Maternal strategies for mitigating neonate predation risk during the postpartum period in Thomson’s gazelle. Behaviour 151: 1229-1248. PDF Roberts BA. 2012. An attack by a warthog (Phacochoerus africanus) on a newborn Thomson’s gazelle (Gazella thomsonii). African Journal of Ecology 50: 507-508. PDF