Preening

Preening

A bird’s feathers are light-weight, delicate structures. Birds depend on their wing feathers for flight, and the feathers on the body need to be kept smooth and aerodynamic, so that the bird can fly efficiently. The feathers are vital for insulation, to keep warm, and for waterproofing, to keep dry. So the feathers need to be cared for. This process is called preening. As a very rough average, birds spend an hour a day preening themselves.

This male Cape Sparrow is preening its neck
This male Cape Sparrow is preening its neck. Birds often fluff out their feathers like this because it makes individual feathers easier to grasp. BirdPix record 282934

While preening, a bird gently pulls each feather through its beak. This helps to keep the feathers clean and intact. Almost all species have a preen gland at the base of the tail. The preen gland is also called the uropygial gland. It produces a complex oily substance which the bird rubs through its feathers. The chemical analysis of preen oil has generated several PhDs and lots of papers in journals. The preen oil contains waxy compounds which help keep feathers waterproof and stops them from becoming brittle. In some species, the preen oil also contains chemicals which have been shown to be anti-microbial, so that preening reduces the impact of bacteria and lice that eat feathers.

Preen gland of a Laughing Dove

The feathers on the head are out of reach of the beak. These get preened by being scratched by the feet. Preen oil is collected from the preen gland by the beak, transferred to a foot, which then scratches the oil into the feathers.

Allopreening

In some species, the preening of the hard-to-reach feathers around the head is done by the mate, especially during the breeding season. This behaviour is called allopreening. Hamerkops and African Red-eyed Bulbuls are examples of species which engage in allopreening. When birds of a pair preen each other at the same time, we say they are doing mutual allopreening.

Preening, oil and petrochemical poisoning

When a bird, and especially a seabird, gets oil on its feathers, they lose their waterproofing, and the bird preens then diligently in an effort to clean the feathers and become waterproof again. This is a recipe for disaster. Inevitably, oil gets transferred from the feathers to the bill, is consumed by the bird and goes into the digestive system. So the most urgent problem experienced by a seabird caught up in an oil spill is not the oil on its feathers, but the reality is that it is suffering from petrochemical poisoning. An organisation such as SANCCOB is especially successful in getting oiled seabirds cleaned and back into the wild because they are experts in the emergency treatment of petrochemical poisoning.

Preening by these African Penguins has transferred the oil inside them
The most urgent problem faced by these African Penguins is not the oil on their feathers, but the oil they have ingested by preening, trying to remove the oil and to restore their waterproofing. BirdPix record 282923

… and ultimately the feathers do wear out …

In spite of all the care which birds give their feathers through preening, they ultimately get worn and brittle. For most feathers, the “best before” date is about a year after manufacture. Most bird species replace most of their feathers on an annual basis, and that process is called moult.

Further resources

There is a detailed entry on preening in Wikipedia.