pigeon Oil Gland pigeons
By Dr. Türker Savaş

One of my German friends told me about his observation while back. According to him, pigeons with 14 or more tail feathers do not have the oil gland above their tails and they are much more vulnerable to diseases. I did a small research on this:

Commonly known function of the oil gland is oiling of the feathers. This function is much less important in pigeons compared to water birds. However, as you know oiling of the feathers prevent water penetration for pigeons in some level also. In the same time by trapping air between the feathers, working as insulation, allows the bird to loose its body heat in a slower pace during the cold days. In my opinion, birds unable to oil their feathers spend much more energy to contain their body heat than the birds with oil glands. Their metabolism, in relation to this, works on heat production much more. There fore, pushes the immune system to second in importance and makes the birds much more sensitive to illnesses.

Studies on oil gland are very limited. Especially for pigeons, it is almost none existent. Because of this, I am going to summarize important points of some of the oil gland studies done on other bird species.

A study of surgical removal of oil gland in rock pigeons shows no effects on the physical and general condition of the birds. A similar study in quails shows no difference in physical growth, body heat and hematological (blood values) between normal birds and the ones with removed oil glands. However, one of the important things to keep in mind is the limited observation period of both studies.

Another study on titmouse "Parus" shows a positive relationship between the size of the oil gland, amount of oil secretion and the amount of feather mites that lived on each bird. The birds with large oil glands and high oil secretion have more feather mites on them. Researchers conclude, the smell of the oil gland secretion has an attractive effect on the parasites. According to this, the breeds with no oil glands have an advantage over others against the parasites.

I also want to talk about an interesting study:
This is done on chickens. Number of chickens are divided into two groups and the oil gland of the chickens in one of the groups removed. When these birds were examined after 60 days, the type of microorganisms on chickens with out oil glands were found to be different than the chickens with oil glands. While non-pathogen (type that does not cause sickness) microorganisms were found on the normal chickens, the chickens with out the oil glands had pathogen microorganisms. Non-pathogen microorganisms on the normal chickens also prevented pathogen microorganisms from multiplying by their antibiotic secretions. Oil gland must be functioning as a nutrition source for the microorganisms that symbiotically live on the birds.

Besides this, it is a known fact that the oil gland secretion works as a fungicide on birds.
All of these findings make the idea of birds with out the oil gland being more open to illnesses sound real.