An engrossing avian beauty routine

An engrossing avian beauty routine

Spick and span

A house sparrow preening itself. Photo by Jagpreet Luthra

Birds look disheveled and unrecognisable as they vigorously clean their plumes. These painting and polishing sessions of birds are part of their grooming routines. Most birds do this several times a day. Called preening, it involves digging the bill into the base of the body close to the tail to take out a greasy substance called preen oil from the uropygial gland. Then, the bird sets about coating the feathers with the oil to keep them strong and flexible.

The engrossing exercise makes the birds vulnerable to predators, but the survival instinct ensures that birds usually preen sitting on high perches and in thick foliage where they are out of view. Even otherwise, a lot of intelligence goes into preening. In winter, preening is done after sunning that makes the wax more liquid and easier to spread; in summer, bathing and dusting also accompany it. However, preening is not only about oil paint on the feathers. It is a painstaking process of removing body lice and other parasites with systematic pecking, followed by stroking every feather from its base to its tip for a proper alignment to make it flight-friendly.

Flexibility is the name of the game in preening but even so there is no way for a bird’s bill to reach its head and neck. That is where the feet get used, but they just about scratch the head. The rest of the cleaning is done by the commonly seen dust and water head baths, also by allopreening, in which birds, especially mates, clean each other.

Preen oil has substances that inhibit bacteria and parasites both externally as well as internally. A study by zoologist Sergio Magallanes from Spain, published in the Journal of Avian Biology in 2017 — about the incidence of malaria in house sparrows — found that uninfected birds had larger uropygial glands and higher anti-microbial activity in those glands than in the infected birds. Another fossil study three years ago at the oxygen-poor oil shale deposits of the Messel Pit fossil site in Germany came as an astonishing example of the anti-bacterial component of the preen oil.

This study, done by Senckenberg Research Institute and Natural History Museum, made a sensational discovery, a 48-million-year-old skin gland from a bird, containing preen oil. Scientists assume that the anti-bacterial property of the oil may have prevented bacteria to settle in after the bird’s death, thereby, inhibiting its decomposition. Normally, soft parts of an animal, unlike bones and feathers, decompose within a few years.

The preen oil gland, therefore, is among the most vital parts of a bird’s health. How much preen oil does a bird need in its lifetime? That depends upon the number of feathers, which vary according to the species, age, and the season. According to International Centre for Birds of Prey, most small songbirds have between 1,500 and 3,000 feathers. The lowest recorded number of feathers is 940 for a humming bird and the highest is 25,216 for a swan. Grooming such a large number of feathers obviously requires time and devotion.

A bird spends an average of nine per cent of its daily time or an hour and a quarter on preening, but it can go up to three hours a day. Largely, males spend more time on their plumage because better maintenance means better mating chances. Water birds like ducks need higher maintenance. Feathers, according to Ian Robinson, author of Handbook of Avian Medicine, “are waterproof by their intrinsic nature” but “over time, exposed to environmental insult, abrasion, immersion in water and ultraviolet rays, become dry and brittle and tend to break.” That is where preen oil becomes useful. However, not all birds have an oil-producing gland; some, like owls, pigeons and parrots, have a powder at the base of the tail with which they spruce up the feathers.

Powder or oil, birds need it for beauty and health—just like us.