Starling (Sturnidae): biology, behavior, distribution, and human interactions

Size and weight

The starlings (Sturnidae) are small to medium-sized songbirds (Passeres) from the order of passerine birds (Passeriformes). Among the smallest and lightest starlings are the species from the genus Poeoptera, such as the Kenrick's starling (Poeoptera kenricki) with a length of about 15 cm and the Abbott's starling (Poeoptera femoralis) with a weight of about 34 grams. The largest starling is the Long-tailed Glossy Starling (Lamprotornis caudatus), up to 54 cm in length, of which about 60% is the tail. Among the heaviest starling species is the White-collared Starling (Streptocitta albicollis), weighing up to about 290 grams and 50 cm long. This makes it approximately as large as the Long-tailed Glossy Starling, but about twice as heavy.

Plumage and colouring

Their plumage is varied, from typically black or dark monochromatic species such as the Monochromatic Starling (Sturnus unicolor) to multicolored species such as the Magnificent Starling (Lamprotornis splendidus), whose plumage has a metallic sheen. The sheen ranges from slightly shiny metallic colors, as in the starling (Sturnus vulgaris), to highly iridescent, shiny metallic colors, as in most species in the genus Actual Glossy Starling (Lamprotornis). The iridescent effect is produced in four different ways.

All starlings, including African starlings, get their iridescent plumage sheen from rod-shaped melanosomes in the melanocytes, which produce the pigment melanin and are arranged accordingly under a thin film of keratin. The refractions of light (interference) at the keratin film cause the metallic sheen of the colors. Three other forms of melanosomes that are optically relevant have been identified in the feathers of African starlings. One form is characterized by flatter melanosomes, which allow the structures to be thinner and more densely packed or to form multilayers. Another form consists of hollow melanosomes that cause strong optical refractions of light at the interfaces between the air and melanin, creating structural colors without the presence of pigment. The third form consists of a combination of the two previously mentioned in platelet form, affecting coloration by both single-layered, multilayered, and alternating arrangement of platelet forms. In total, however, only one of these variants occurs per species.

Eyes

The avian eyes of starlings and probably most other bird species (except, for example, nocturnal birds) see their environment differently than we humans do: Starlings have four types of photoreceptors (also called photoreceptors) on their retinas, not just three. In addition to the thinner rod-shaped receptors (cellula optica bacilliformis) responsible for black and white vision, starlings have four cone-shaped receptor types (cellula optica coniformis) responsible for colour vision (tetrachromatic vision). Three of the four cone-shaped receptor types cause the perception of the three primary colours red, green and blue in the range of light visible to humans (trichromatic vision). The fourth receptor is responsible for the absorption of the short-wave ultraviolet light, 1-380 nm (WHO), which is not visible to humans. The incidence of light stimulates the different receptor types within the highly folded membranes, which are provided with different coloured oil droplets, to different degrees of intensity. The respective receptors react differently to the different wavelengths of the light, so that the different colours and hues are perceived. The additional UV receptor compared to humans allows starlings to perceive our environment in a much more differentiated way than humans. Thus, starlings are able to better recognize differences in conspecifics and in the degree of ripeness of fruits or other UV-reflecting traces.

vocalizations

Starlings make complex and varied sounds that are a form of communication. Some species use their talent to imitate the sounds of other animals and bird species. By imitating a predator or warning calls, they drive away competitors in a feeding contest and can thus gain an advantage in the search for food. Others also imitate parts of human speech or car alarms.

The species feed essentially on insects and fruits, with certain species specializing in particular insects and/or fruits. However, most starlings have a wide variety of species and types of these on their menu, and occasionally feed on nectar. Starlings have often also tapped food scraps from humans as a food source, such as the Red-shouldered Glossy Starling (Lamprotornis nitens), and are therefore often considered omnivorous.

Most species of starlings are gregarious and usually occur in smaller and larger groups to large flocks outside the breeding season. Depending on the species and region, groups of hundreds to thousands of birds travel together and like to invade fruit-growing areas, where they sometimes destroy significant parts of the harvest. Fruit growers try to protect themselves from this in a variety of ways. Nets over the fruit-bearing plants have been widely accepted as the best affordable and effective protection. In Europe, during bird migration from northern Europe to North Africa, formation flights (murmurations) with up to millions of birds have been observed. In some countries, such as Italy and Egypt, starlings are caught with large nets, especially at this time, and are then frequently consumed.