Love all the pictures. I always try to capture pictures of the eyes. especially the eyes of an elephant with their long eye lashes.
We spend our days traversing Londolozi’s incredible surrounding environment, observing the weird and wonderful creatures and their interactions that take place all around us. The more time we spend in and amongst the wilderness, the more we are tempted to try and better understand the behaviour of these different animals. And one can start to do this by simply observing…
By focusing on the outward appearance first, start to notice the fur/leathery coat, the claws and/or paws, the fine-bristle hairs on the chin or the long eyelashes, the position and size of the ears and their eyes… Once we start to hone in on the power of simple observation, we begin to awaken to the interpretation of certain behaviours, with one of the most important questions (in my opinion) being:
“Why is this animal behaving in this particular way?”
What I have come to realise is that this question is equally entangled with another question about evolution:
“Why has this animal evolved to be what we see today?”
As Robyn Morrison so aptly discusses in one of her latest blogs, species have evolved over thousands of years through the process of natural selection.
Darwin argues that organisms with traits that are beneficial for survival and reproduction are more likely to pass those traits on to their offspring, while organisms with less beneficial traits are less likely to do so.
As a result, the population gradually changes over time, with the traits that are most beneficial for survival and reproduction becoming more common. This process, Darwin argued, could explain the diversity of life on Earth and how different species have evolved over time to best suit the environment that they occupy.
So in this instalment blog focusing on structural adaptations, I wanted to focus on the organ that we as humans rely on the most when it comes to observing the world and wildlife around us: eyesight.
“An animal’s eyes have the power to speak great language” – Martin Buber
At a high level, below are several structural adaptations of the different types of eyes and eyesight found in the African wilderness.
Many animals have large eyes that allow for better vision in low-light conditions. For example, the eyes of nocturnal animals such as lions, leopards, and hyenas are large and circular.
Within any eye’s retina, there are two types of cells, rods and cones, that are receptors responsible for one’s sense of sight. These receptors are part of the eye and are responsible for converting the light that enters your eye into electrical signals that can then be interpreted by the brain.
Rods are responsible for picking up the amount of light and are essentially important for vision at low light levels (“scotopic vision”). They do not mediate colour vision and have low spatial perceptivity. I will touch more on cone cells under the section on colour vision.
In addition to the above, predatory animals’ eyes (lions, leopards, and cheetahs for example) are forward-facing and provide binocular vision. This allows them to accurately judge distances, stalk and capture their prey. A combined field of view from the overlap of two eyes allows for greater depth perception and the ability to accurately determine distances between objects.
Compared to the binocular vision of many predators, we find that many prey species have more of a peripheral field of vision. Many antelope, for example, have their eyes situated on the sides of their faces to give them a greater field of view. This allows the best opportunity to spot any predator sneaking towards them from all angles. We know that prey species often like to spend their evenings congregating in groups in open clearings when they feel more vulnerable in the dark, so peripheral vision helps the many eyes and ears scan in the dark for any potential danger!
Many nocturnal predators and prey species have a tapetum lucidum, which is an additional reflective layer at the back of the eye that enhances their ability to see better at night. The light passes through the cells of the retina and encounters the tapetum lucidum, which reflects it back through the retinal cells again. A ‘double-take’ as such. It allows them to see more clearly in low-light environments, as well as allows us to safely shine the spotlight on them in the evenings on our way back to camp without having a negative impact on the vision of the animal.
“The tapetum lucidum is a biologic reflector system that is a common feature in the eyes of vertebrates. It normally functions to provide the light-sensitive retinal cells with a second opportunity for photon-photoreceptor stimulation, thereby enhancing visual sensitivity at low light levels.”
Certain animals, such as primates (vervet monkeys and chacma baboons) and birds, have a greater number of cone cells in their eyes, which allows them to see better in colour. This allows them to distinguish between greater shades of colour, which is useful for locating ripe fruit, identifying predators, and attracting and identifying the reproductive status of the opposite sex.
Cone cells are active at higher light levels (“photopic vision”), are capable of colour vision, and are responsible for high spatial perceptivity.
Several animals have extraocular muscles that allow them to rotate their eyes to a greater degree than humans. For example, chameleons have eyes that can move independently of each other, giving them a 360-degree field of vision. This allows a chameleon to watch an approaching object while simultaneously scanning the rest of its environment.
Several animals have a nictating membrane, or third eyelid, which is a transparent membrane that can be drawn across the eye to protect it from dust, debris, and bright sunlight.
Overall, the physiological structure of the eye and respective eyesight of African wildlife animals have evolved to provide them with the best possible vision for their respective environments, whether it is to locate prey, avoid predators, or navigate their surroundings.