There is a very small impala lamb that has been seen over the last few days just to the west of Pioneer Camp. Since the local impala lambing is seasonal, and the vast majority of births take place during November and December, we can deduce that something didn’t quite go according to plan for the mother in question. Not that she had a plan, but either her genetic clock was out of whack or something just happened to make her fall pregnant a good few months later than the rest of her conspecifics. Either way, her lamb has been born far, far later than usual.
Impalas are the most successful antelope out here. Just ask anyone who has been on a game drive at Londolozi or any of the surrounding reserves; they would have seen hundreds.
One of the keys to their success is their breeding strategy, in which births are synchronised among the females to coincide with the onset of the rains. To achieve this, the mating season (or rut) occurs in May-June, allowing for the average gestation period of between 190-200 days to end at roughly the time the first thunderstorms are building and releasing their bounty on a parched bushveld. The resulting surplus water and fresh grass and browse material ensures that the females have enough food as well as enough cover in which to give birth away from prying eyes.
Just how did this particular female manage to conceive so much later than the other impala ewes though?
It’s not only her reproductive cycle that must have been somehow out of sync, but the chances of being impregnated by a ram would also have been significantly reduced, as the sperm count of the males has been recorded as being 25 times lower in the Spring (September) than in Autumn (May/June, when the rut is happening).
In a paper entitled The Sexual Cycle of the Impala Ram Apyceros Melampus Lichtenstein, J. D. Skinner found that:
There were probably not enough spermatozoa present in the epididymis in September and November to ensure a fertile mating. In any event, libido would be much reduced and it would not be possible for more than one or two ewes to conceive at this time. It would appear therefore that the mating season is partly dependent on the physiological status of the male at that time – J. D. Skinner (1971)
Some interesting information there, with all the evidence pointing away from females conceiving in September, which if we go back about 6 months must have been when the female in question was impregnated.
I don’t want to get into the reproductive cycle too much here, but rather focus on this single lamb that has been found. I don’t know whether it’s a male or female but for simplicity’s sake I’ll refer to it as male.
He’s going to have his work cut out for him, that’s for sure. One of – if not the single biggest – advantages of all the lambs being born together over the period of a few weeks is safety in numbers. Little creches form, with large nursery herds providing some kind of protection from predators, whose primary food source during the start of summer is impala lambs. “Protection” is probably the wrong word, but if you’re with 100 other lambs, there’s far less chance the approaching leopard will focus on you specifically.
And that is where this little impala is going to struggle. His mother is balancing on a double-edged sword here, as she needs to keep him out of sight, but the thickets that provide cover are exactly the type of habitat through which a predator could stalk most easily. Should the mother introduce the lamb to a herd, it would automatically be the focus for a predator eyeing them out.
Thankfully the territorial Mashaba female has been seen mating far to the south with the Inyathini male, so probably won’t be in the area for another couple of days, and the Flat Rock male has just finished an impala kill a few kilometres away, so neither are likely to present an immediate threat to the lamb. The Tsalala pride are north of the river, and we haven’t seen any wild dogs for a few days. His biggest threats are therefore accounted for.
I imagine that in a few short months (impala lambs grow incredibly quickly), the size differences between him and other lambs from last season won’t be as apparent, and he’ll be able to blend in with the rest unobserved.
Let’s hope this is one little impala that has the tenacity (and the luck) to beat the odds make it through winter.