Shake your uropygial gland
Evan Zabawski | TLT From the Editor September 2020
The importance of preening.
This aspect begat the expression, 'like water off a duck's back.'
There are more reasons birds nibble and stroke their feathers than one might think. The most commonly known reason is to smooth and align their feathers for peak aerodynamic efficiency, while another reason gives rise to an idiom, but there is some debate regarding the precise mechanism behind their function.
This act of grooming is called preening, and it can occupy several hours of a bird’s day, especially during molting when preening removes the tough sheaths from newly molted feathers to allow them to align properly. One of the key functions of preening beyond shaping feathers is removal of dust, parasites and lice. This aspect of preening can be augmented by bathing or sunning, but some species will engage in another step called anting. Anting involves laying on an anthill and rubbing ants over their body while preening to distribute formic acid over the feathers. This is believed to inhibit parasites than can damage feathers.
Another coating applied to the feathers originates in a gland located at the base of a bird’s tail. The gland is sebaceous, meaning it emits oily matter called sebum, like those found in mammals at the base of each hair follicle where the sebum lubricates the skin and hair. In birds, the oil moisturizes the feathers to keep them flexible and strong so they can withstand the stress of flight.
The majority of birds have a single, large gland called a uropygial gland (from the Ancient Greek οὐρά [oura] “tail” and πυγή [puge] “rump”) that secretes preen oil from a papilla. This singular source explains why a bird seems to preen its tail feathers more than anywhere else. In reality, it is coating its bill and head with oil and spreading it over the rest of its feathers, so the bird must constantly return its head to the papilla for a fresh dose of preen oil.
Preen oil is widely thought to act like a waterproofing agent, though studies that have either blocked access to the gland or removed the gland entirely were not successful in identifying if the increase in water retention was due to a hydrophobic nature of the oil or that it simply aided in maintaining feather structure. What is certain is that in other experiments where birds were coated in preen oil, or other oils, the coated birds did lose heat more slowly and became less wet than a control group.
This aspect begat the expression, “like water off a duck’s back,” since this is the area of the bird having the highest concentration of preen oil at any given time, but also an area most easily flicked back and forth to fling away smaller droplets of water. The expression is generally used to imply an insult or negative comment having no effect on the recipient, whereas “shake your tail feathers” implies a desire to dance.
Some birds also shake their tail feathers as part of dance to attract a mate, and preening certainly promotes a healthier, and, therefore, more desirable appearance. Preen oil in female birds has been shown to change composition during mating season, but it is unclear if this is part of the seasonal changes like crypsis (antipredator adaptation) or if it is a pheromonal attractant.
A change observed in preen oil of male birds is an increase in the wax content, which has been shown to increase the brightness of a bird’s plumage, thereby increases its chances of attracting a mate. In some species of birds, the preen oil might be pigmented red, orange or yellow, which makes preening akin to application of make-up. Once successfully attracting a mate, some birds engage in mutual preening, called allopreening.
Clearly preening is not only an important part of a bird’s day-to-day existence—it plays a part in its subsistence in nature.
Evan Zabawski, CLS, is the senior technical advisor for TestOil in Calgary, Alberta, Canada. You can reach him at ezabawski@testoil.com.