Energy-efficient feeding strategies

Sabi Sand | December 2016

Life in the wild is all about energy-related equations, and it is a simple fact that no organism can continue to thrive for an extended period if the expenditure of energy in the quest for nutrition exceeds the amount of energy gained from the intake of nutrients. Indeed, a point may be reached, after too prolonged a period of negative energy returns, where survival is no longer possible. This concept can be used to explain why, as a result of the recent extended drought (which we hope may have now been broken), many buffaloes have perished, without necessarily having been killed by predators. During the drought, especially towards the end of it, the amount of suitable grazing to sustain the buffaloes became very limited, and it seemed that the majority of buffaloes were not able to engage in an energy-efficient feeding strategy, therefore there was a decline in their general condition. Some of the weakened individuals fell to predators, mainly lions and hyenas, but in at least one case, to a pack of painted hunting dogs. Some simply became thinner and thinner, and eventually died of starvation, not having sufficient energy reserves to go and seek out food sources further afield. Interestingly, the buffaloes that seemed least affected by the drought-related conditions, were the mature males. Could this be because they were better able to utilise the limited resources available, showing greater initiative in terms of resorting to browsing from trees, feeding on the relatively coarse Phragmites reeds, and basing themselves in areas where there was at least some decent grass available?

Or, and I am of the opinion that this is more likely, is it that the limited energy reserves of the adult female buffaloes were being exhausted in their reproductive processes, while the younger buffaloes would have needed to draw on their energy reserves to allow for any growth to take place? In a situation like the latter, where there is a conflict between maintaining condition and actually growing, the result can be stunted growth.

While it has been a tough time for buffaloes, hippos and a few other herbivores, it has been a time of plenty for some of the carnivores, and as mentioned in previous journals, the kills analysis statistics have been very skewed. The wheel turns, however, and the time will soon come again when some of the carnivores have to work much harder for their meals. The 12 cubs of the Mhangene pride have had the best possible start to their lives, as their mothers have been making buffalo kills almost at will, and have thus been excellent providers for the last few months. The vast majority of their kills over this period have been buffalo. It is true that we have also seen them on waterbuck, zebra and impala kills, but the predominance of buffalo meat on their menu has been extraordinary. My opinion is that when buffaloes are in really good condition, the majority of interactions between buffaloes and lions end up with the buffaloes having the upper hand, and chasing off the lions.

The Mhangene pride has always been an effective buffalo hunting unit, however, and the weakened state of the buffaloes has led to the percentages swinging heavily in favour of the lions. Even a small pride like the Othawa pride has been harvesting buffalo on a regular basis. Come the good rains which we are hoping will fall this summer, and we should see a gradual strengthening of the buffaloes, and as their condition improves, so too will their energy levels, which will allow them to travel further in search of good grazing, or to move greater distances after encounters with lions. They will also offer a lot more resistance when lions are hunting them.

The Mhangene pride (and most other lions, for that matter) will no longer have it so easy; things will not just keep going their way indefinitely. Some tough times lie ahead for the Mhangene pride, especially as the cubs grow older and larger, and require more and more meat to satisfy them. Those lionesses are going to have their work cut out for them, especially if they are having to kill more medium-sized game animals again, which will place higher demands on their skills and will probably require a significantly higher expenditure of energy.

I sometimes like to compare active hunting and passive hunting strategies employed by various predators. While one could say that some species of predators, such as cheetah, are generally more likely to use active hunting methods and others, such as crocodile, are generally more likely to use passive hunting methods, individuals within a species will also differ in how they go about acquiring food. The key for all of them, is to be adaptable, and to use methods that will work best for themselves, according to the set of circumstances that prevail at the time, in order to derive maximum reward per unit of energy spent. A young male leopard might discover that a good method for him to hunt might just be to wait patiently, well concealed, at a frequently used animal path that leads to a waterhole. On a hot day, he could lie in the shade and just wait for something to come along, and only pounce or make an attempt when a suitable prey animal is really close. A similar strategy may be to position himself on a termite mound, very close to the entrance to a burrow used by warthogs. These are examples of passive hunting, and they can be very effective, as a leopard might make a few consecutive kills over a period of several days, without having to go very far. It is a method that requires patience and then proper execution in order to bring positive results, but it certainly has its merits. By hunting this way, and keeping a low profile, a young male leopard (or indeed a really old one that is no longer territorial) could exist within the territory of a prime adult male without challenging him. Not for a moment am I suggesting that territorial male leopards do not also engage in passive hunting. Of course they do! They probably do it as much as they can, if it brings in the rewards. What I will say, however, is that once he has finished feeding on a kill that has kept him busy for a couple of days, a territorial male leopard is far more likely to go on a long walk, patrolling his territory and scent marking as he goes. He needs to strongly advertise his presence in his territory, otherwise potential rivals will be more likely to move in and challenge him. I sometimes think of a leopard with a full stomach as being rather like a vehicle with a full tank of fuel. It has the energy reserves to take it a long distance.

If conditions do not favour a predator or group of predators, they may decide not to hunt, even if very hungry. For example, I have seen a very lean pride of lions on a still, moonlit night show no intention whatsoever of trying to hunt the large herds of impala, wildebeest and zebra that roamed in the open areas a few hundred metres away from them. The lions knew that their chances of success were slim, so rather than waste their energy reserves, they would prefer to conserve their energy until conditions changed to suit them better.

In Nature, the balance between survival and non-survival is often a very delicate one, and it is only by successfully managing the energy equation that organisms are able to thrive, or indeed to survive at all during long periods of challenging circumstances.