African Wildlife & Environment Issue 85

BIRDING

Breeding The nesting period is from October to February in Botswana and October to January in South Africa and Zimbabwe They build the nest in spaces such as tree holes or crevices from two to six meters above the ground, also holes in river banks and even in hollow steel fencing poles. Nesting material includes green leaves, dung, and

First of all, it’s important to note that there are two types of plumage colouration, as happens in butterflies and other animals: first is pigment-based colour, including melanins, carotenoids, and others, which make up a small colour palette.The second is structural colour. This results from the effect of light on nanostructures. Iridescent colours are often the result of the feather’s structure, through which a wide range of iridescent colours is possible. Tiny follicles in the epidermis, or outer skin layer, produce keratin proteins that form the feathers. The barbs correspond to each ‘hair’, which branches perpendicularly into barbules. In turn, these barbules branch into barbicels. The barbicels of the adjoining barbules hook together in the feather, giving it its structure. In plumage, structural colouration is the product of nanoscale arrangements of various elements like keratin plaques, melanosomes, and also the air inside the feather barbules. Of course, the same bird species can have feathers with colours produced by different mechanisms and pigments. Furthermore, it is common for the same plumage to present combinations of both mechanisms. ‘Melanosomes’ are small bundles of melanin found in the feathers, skin, and fur of many animals that can produce structural colours when they’re properly organized into solid layers. Why are the colours of the male Violet backed Starling so bright? As we mentioned above, structural colours are formed by the ordering of thermodynamically stable nanostructures in, for example, hexagonal symmetry. In general, in the plumage of many birds, the melanosomes involved in the arrangement are solid, which leads to low colouration variations. Thus, to achieve brighter or more saturated colours, one of these two conditions must be met: • Improving the contrast of the refractive index • Increasing the relative amount of low refractive index material

other plant material. The nest is a shallow cup built of grass and twigs by both sexes. Green leaves are added throughout the breeding period. They will re-use their nests in consecutive breeding seasons. The female incubates the clutch of two to four eggs, which are pale blue with reddish/brown spots, for 13–14 days.The male will help feed chicks until they fledge after about 21 days. Notes on feather colouration In nature, colour patterns are a key element for sexual selection. Often, the colouration of species plays a role in inter and intraspecific communication. It’s interesting to know that the different patterns found in nature have hardly been investigated, perhaps due to how hard it is to effectively capture their variability with the usual methods.

59 | African Wildlife & Environment | Issue 85 (2024)