BIrds and their Feathers
by Paul Laurie
Birds generally re-grow their feathers once or twice a year to enable the bird to retain a warm and waterproof layer that is kept in good order, as a birds life depends on its plumage.
Feather wear due to abrasion and also become weathered by the sun and in the case of birds associated with the sea, salt also acts as a wearing agent. Birds spend much of their time cleaning and oiling the feathers to keep them in pristine condition, a bird in poor condition is a likely target for predation and will be unable to retain body heat and likely to suffer from hypothermia. A birds feathering provides a layer that the bird uses to control its body temperature. By pushing the feathers out and trapping air in layers underneath the feathers a warm area develops. The bare parts, which are not feathered, are often placed within the feathers to help retain body heat. This is common in roosting waders, which have long legs and bills in comparison to the body size, and standing on one leg and with the long bill tucked into the mantle & back plumage will help retain the birds body temperature. During hot spells of weather birds are able to sleek down the feathers close to the body enabling the body to keep a constant body temperature, this is often combined with panting which also helps reduce body temperature. Birds spend much effort in oiling their feathers and keeping them waterproof, this is an important ritual to ensure the long life of the feathers removing damaging fungi and bacteria, to ensure they are in the optimum condition for feeding, swimming and escape from predation as well as enduring heavy rain or very humid conditions in the tropics for example.
A passerine does not need the same waterproofing as say a Guillemot that is pelagic during the autumn & winter spending months at sea, therefore the oil gland on a Blackbird is not as efficient as on the Guillemot but is equally important. If a bird is not feeding/hunting or roosting then it will be preening. Often when confronted with a bird with a deformed bill, which is not uncommon in waders for example, birders are often concerned that its feeding ability my be affected, however it is far more likely to have much more difficulty in preening and keeping its feathers in pristine condition and therefore reducing the birds chances of survival. Preening includes cleaning the feathers, rearranging misplaced feathers and oiling. Birds are often observed scratching their heads and rubbing the head on the underside of the wing, this helps distribute the oil onto the head where the bird can not reach with its bill. For example imagine a Curlew trying to reach its crown feathers!
Feathers are lifeless structures that cannot be repaired and so when lost or damaged they must be replaced. The durability of a birds feathers are associated with it's life style and moult and this can be illustrated by imaging a Guillemot and a Robin that spends much of its life on and in a cold sea in often adverse weather conditions be it storms or strong sunlight, which causes bleaching. Guillemots have large oil or preening glands the produce copious amounts of waterproofing oil and they spend much of their time preening and caring for their plumage. How often do you see a Guillemot stand up and shake its wings to remove excess water in preparation for preening. A Guillemots plumage is mainly black which contains the pigment melanin; this dark pigment is a hardwearing colorant that prolongs a feathers life.