House Sparrows: plumage quirks
Updated: Feb 2, 2021
Feathers are a unique characteristic of birds, they are composed of beta-keratin and must be renewed periodically in a process known as molting. A bird's feathers have several important functions, such as controlling body temperature, protecting from sun radiation, aiding in nest building, camouflage and as a form of communication in the form of visual signals to mates or rivals.
The house sparrow is a species native to Eurasia and North Africa. It has been introduced into a large number of countries on all continents except Antarctica, Alaska and northern Canada. It is small and is a bird that is adapted to the urban habitat to the point of being the most common and well known.
The plumage of the house sparrow is dominated by brownish tones on the back, with marked black and grayish stripes on the obispillary, breast and belly. Males in the breeding season have a black bill and a reddish back, the crown is gray and the bib becomes more extensive and darker. In males, the beak is discolored in winter.
The females have a brownish appearance, with a brownish crown and a clear line behind the eye, no black on the throat, and a grayish bill at the ends and yellowish at the base. Young males are indistinguishable from females until they molt in late summer, when they acquire adult coloration. There are variations in the plumage of the house sparrow caused by genetic or environmental factors, these variations are known as leucism and albinism. These types of plumage aberrations in house sparrows are more common in cities and small towns, and occur in 12% of individuals, compared to rural areas where the frequency of albinism is close to 0%.
Leucism is caused by a recessive gene, and birds with this genetic trait have characteristic normal eye coloration and normal vision, so they tend to live longer. House sparrows with leucism are not more sensitive to sunlight, they do have pigments in soft parts, since they do not lack melanin completely, only a proportional part.
In the case of albinism in the house sparrow, it can be caused by age, disease, low environmental quality or diet and also by a series of genetic mutations that totally or partially reduce the melanin pigment in the eyes, hair or feathers of the animals. The lack of pigment in the iris of albino animals causes the blood vessels to show, giving them their usual reddish hue. Albino birds usually have pink or reddish eyes, pale beaks and legs, as well as pale skin.
Albino birds show a greater than normal deterioration in their plumage, since the lack of melanin in a bird's feather results in a plumage that is not as cohesive as a normal plumage. In terms of reproduction, albino birds may be hindered in trying to reproduce because plumage plays an important role in courtship displays.
In North America, one of the species with the highest incidence of albinism has been found to be the house sparrow. Although house sparrows live in close proximity to humans and their buildings, an individual with albinism or leucism is at much greater risk of not surviving in the wild, as it is an easier target for predators. Although they are found in cities, towns, suburbs and farms near livestock, their main predators include domestic cats and increasingly common urban birds of prey
such as hawks and owls.
If total or partial albinism is a reflection of genetic or environmental problems, it is important to document records of this abnormal coloration to be used as indicators of environmental or genetic problems should the incidence increase.
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