Saturday, March 16, 2013

Sunbathing Chicks

People usually see sunbathing as a recreational activity done by beach goers looking to add glow to their skin tone.

For many people, getting vitamin D3 is not something that we often worry about, even though it is a very necessary supplement. This is mostly because it is easily absorbed by our bodies without us even knowing it.  For most birds, however, there is a very intricate process for them to obtain their needed vitamin D3 supplement.  Most birds have a gland called an uropygial gland that allows them to not only obtain their vitamin D3, but also may help them to ward off insects, improve their waterproofing, reduce bacteria, and help maintain the general health of their feathers, scales and beak.
 Inset shows a close-up of the uropygial gland on this owl
The uropygial gland is located dorsally on the bird’s back at the base of the tail and is covered by a bird's feathers until they preen (running their beak along feathers, scales, skin, etc. to clean, straighten, or move their feathers).  The bird touches the gland with its beak, which releases the oil that the gland produces.  The gland has two lobes that may sometimes (depending on the bird species) have a ring of down feathers surrounding the opening (a nipple-like structure called the papilla) which acts as a wick for the oil it secretes.  When a bird moves to touch the gland, the bird lifts the covering feathers out of the way, since it can control groups of feathers.  A bird may then spread the oil throughout its feathers with its beak.  Some birds can rub their heads and feet on the gland as well.

The oil secreted from the uropygial gland contains vitamin D precursors and when exposed to the ultraviolet part of the sun’s light, is then altered to vitamin D3. When the bird preens its feathers again, it ingests the vitamin D3 from the oil. Isn’t Mother Nature amazing?
 A typical pose for a sun bathing Bateleur Eagle
So, once the oil is spread, any kind of exposure to the sun allows the process to occur.  A bird will sometimes perch in an area that allows it to receive ultimate sun light access; and to further its sun absorption even more, some birds will do something called sunning.  This is where a bird stretches out its wings and will either face its back towards the sun or it may also (in a Bateleur Eagle’s case) face the inside of its wings towards the sun. 
 This bird shows a typical preening posture
Along with the vitamin D3 process, the gland’s oil helps birds out in many other ways.  Spreading the oil along their body surface can help to reduce organism growth and certain lice and mite infestations in the feathers and on the skin.  Even though birds’ feathers are already engineered to repel water readily, this gland secretion adds extra waterproofing as well.  It can be smelled on the female and nestling Hoopoes (a colorful Eurasian and North African bird), giving them a special smell to the males of this bird. The oil helps to give Musk Ducks their musky sent during mating season and Storm Petrels (a tube-nosed sea bird) can actually identify their relatives by scent because of this oil.  Some studies are being done about whether a female bird’s oil coat looks different compared to a male bird’s oil coating. This is because diurnal birds can see light in an ultraviolet range; humans cannot.

Although the uropygial gland is very useful to birds, there are a few species of birds that do not posses it.  Some of those birds being: an Ostrich, Emu, Cassowary, Frogmouth, many Pigeons, many Woodpeckers and certain species of psittacines (parrot family: Parrots, Macaws, and Parakeets) like the Hyacinth, Lear’s, or Spix’s macaw.  These birds are able to absorb enough vitamin D3 through their skin so that the uropygial gland, for them, is not necessary.   Even though not all birds need it to survive, the uropygial gland is a crucial organ for most of the world’s birds to maintain a healthy and substantial life.

Submitted by Teresa Aldrich, World Bird Sanctuary Naturalist/Trainer

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