Greetings and Salutations,
Day and night trips always reveal interesting aspects of animal behaviour. Many people have experienced a day safari, but few venture out on a night trip. I would go as far as to say that at night it is more intense. When spotlighting an animal, one is focused on that particular subject, whereas in the day there are all sorts of distractions. These distractions could be the scenery, other animals, birds, or even other tourists. So in the case of a night drive, the focus is concentrated on one particular subject at a time.
This can make it easier to determine animal patterns and gathering, hence the topic of the Ark Effect. There are certain weather conditions that create this feature. In fact, one simple phenomenon is responsible for the Ark effect, combined with a geographical feature. The weather condition I am referring to is the south wind, which normally is present prior to, as well as during the presence of a cold front in this area. The geographical feature is the shape and orientation of the Southern end of the Isimangaliso Wetland Park. As you enter this part of the Reserve, it reveals itself as a narrow waist that spreads northwards to Cape Vidal, getting broader and broader moving northwards. When the south wind blows, browsers and grazers tend to move into and across the wind. Eventually the populations of kudu, bushbuck, zebra, buffalo and wildebeest get sandwiched into a fairly confined area, due to the fence line separating the village of St. Lucia from the Reserve.
When embarking on a night drive when there is a south wind blowing, one may anticipate that good numbers of animals will be found gathering in the fenced area separating the Reserve and the Sleeping Hamlet of St. Lucia. Why do we get this particular phenomena? Well, herbivores tend to graze or browse into the wind for two reasons: predators are easier to detect, and plants react to grazing and browsing. Generally, once certain plants have been eaten, they become toxic or bitter, which represents an attempt to get the herbivores to move away. Plants also tend to release pheromones into the wind, which stimulates the plants situated downwind to become bitter and toxic. Therefore, animals are left with two choices: to move downwind and get poisoned, thus being at risk of being attacked by an undetected predator, or to move into the wind to get sweeter vegetation, which gives them an advantage over any predators in that they are able to detect them more easily.
The long and short of it here is that these animals gather along the fence line, which they are then unable to get through. This gathering makes it appear as though they are almost in a queue to board Noah's Ark. This effect is especially visible during the night, when the spotlight moves from one group of animals to the next, without the distraction of scenery!
Hasta la vista,
The Knait Wrydah.