Why Do Birds Preen?

parrot preening

Story at-a-glance -

  • Preening, which is what birds do when they clean or straighten their feathers with their beak, helps keep birds’ feathers healthy
  • Most birds have a preen gland, or uropygial gland, located near the base of their tail that secretes an oily substance
  • Birds rub their beak and head over the gland and spread the oily substance over their feathers, legs and feet, which helps them repel water as well as potentially ward off parasites
  • In addition to protecting birds from water, the oil produced by the preen gland may help preserve the integrity of feathers as well as possibly the bill, legs and feet
  • It’s also thought that, in some species, the oil may be a precursor of vitamin D, which gets converted into vitamin D when birds are exposed to sunlight, as well as may alter feather color, which may help to attract a mate

By Dr. Karen Shaw Becker

Preening, which is what birds do when they clean or straighten their feathers with their beak, is a way of tending to birds' most prized possessions: their feathers. This seemingly simple act is actually very complex, however, and goes way beyond the simple removal of dirt, dust, debris and parasites. Feathers are essential to a bird's survival, not only ensuring they can fly but also keeping them warm and dry in inclement weather.

If you spend any amount of time birdwatching, you'll notice that birds spend a great deal of time preening, or grooming — and this is completely normal. To understand all that goes on while birds preen, it helps to first understand the fascinating anatomy of a feather, which are unique to birds and their dinosaur ancestors.

Feather Anatomy 101

Birds have different types of feathers, including flight feathers, which give birds an aerodynamic form for flying, and down feathers, which are there to keep them warm. In all, there are seven broad feather types:1

Wing, which are specialized for flight

Semiplume, which are hidden under other feathers and serve as insulation

Tail, which support steering during flight

Down, which are closest to the bird's body in order to trap body heat

Contour, which cover a bird's body and help streamline its shape

Filoplume, which act like whiskers in sensing the position of contour feathers

Bristle, typically found on a bird's head, they help protect the eyes and face

The Audubon describes feathers as "treelike structures" composed of a hollow trunk, or rachis, surrounded by many branches, or barbs. Barbs of flying feathers are further divided into twigs, or barbules, which grow in certain configurations to encourage flying or insulation.2 Cornell University's Bird Academy further explained:3

"Although feathers come in an incredible diversity of forms, they are all composed of the protein beta-keratin and made up of the same basic parts, arranged in a branching structure. In the most complex feathers, the calamus extends into a central rachis which branches into barbs, and then into barbules with small hooks that interlock with nearby barbules. The diversity in feathers comes from the evolution of small modifications in this basic branching structure to serve different functions.

Downy feathers look fluffy because they have a loosely arranged plumulaceous microstructure with flexible barbs and relatively long barbules that trap air close to the bird's warm body. Pennaceous feathers are stiff and mostly flat, a big difference that comes from a small alteration in structure; microscopic hooks on the barbules that interlock to form a wind and waterproof barrier that allows birds to fly and stay dry."

Birds Have a Preen Gland to Help With Waterproofing

The preen gland, or uropygial gland, is located near the base of a bird's tail and secretes an oily substance. Birds rub their beak and head over the gland and spread the oily substance over their feathers, legs and feet, which helps them repel water as well as potentially ward off parasites.

In fact, while most birds have a preen gland, it is most developed in aquatic bird species such as petrels, pelicans, osprey and oilbird.4 In addition to protecting birds from water, the oil produced by the preen gland may help preserve the integrity of feathers as well as possibly the bill, legs and feet.

It's also thought that, in some species, the oil may be a precursor of vitamin D, which gets converted into vitamin D when birds are exposed to sunlight.5 Interestingly, the color of the oil from the preen gland may also serve a purpose in some species.

In flamingoes, for instance, which are noted for their pink coloring that comes from the food they eat, the preen oil is also pink. Male flamingoes, it turns out, spend more time grooming themselves with the oil during the breeding season than other times of year, which turns them a darker shade of pink that, presumably, attracts more mates.6

There's still a lot to be learned and discovered about the preen gland and its oil. According to professor Gregorio Moreno-Rueda, Ph.D. of University of Granada in the journal Biological Reviews, "Our understanding of this gland is still in its infancy. Even for functions that are considered valid by most researchers, real evidence is scarce.

Although it seems clear that preen oil contributes to plumage maintenance, we do not know whether this is due to a role in reducing mechanical abrasion or in reducing feather degradation by keratinophilic organisms."7

Meanwhile, he states that it's unknown whether preen oil helps ward off pathogenic bacteria or lice, or whether it acts as a repellent against predators, makes birds unpalatable or camouflages birds with ambient odors, as some theories have proposed. What is known is that preen oil improves waterproofing for birds, but how it does this — whether by creating a water-repellent layer or improving plumage structure — is also unknown.

Is Your Pet Bird Preening Too Much?

If you're lucky enough to share your home with a captively bred pet bird, you may find that not only does she preen herself, but she also tries to preen you. This is known as allopreening, and it's especially common in parrots, who also preen other parrots (their mates) in the wild. Preening is completely natural and birds know how much they need. However, over-preening (feather picking) can and does occur in pet birds, often as a sign of stress or boredom.

If your bird is engaging in over-grooming or self-mutilation, including picking his feathers that goes beyond normal preening, see your exotic veterinarian as soon as the behavior is noticed for the best advice. Dietary changes and improved environmental enrichment, including plenty of time outside of their cage, exposure to natural sunlight and behavior modification training will be necessary to address the problem.

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