Feather Arrangement

Feather Arrangement
The feathers of birds are actually not evenly distributed, but are designed in limited fields called pterilae and there are small areas that are not overgrown with feathers called apteriles. Exceptions to penguins and kiwi birds whose feathers cover most of his body. Bird feathers can be named according to their fields, namely:
capital tract, which is fur that covers the top, sides and back of the head and continues to the next pterilae.
Spinal tract, fur that extends from the top of the neck to the back and continues to the base of the tail and can continue or separate in the middle.
Ventral tract, starts between the lower jaw branches and extends down to the ventral side of the neck. It usually divides into two lateral planes passing along the sides of the body and ending around the anus.
The apterilae of the lower abdomen and abdomen of some birds, rich in blood vessels during nesting and brood patches. At the time of brooding the fur on the brood patch will fall out and thin skin.

Humeral tract is a pair of pterilae that are parallel like a narrow band that extends backward on the shoulder side.
Caudal tracts include retrices, tail feathers, usually long and strong.
Alar tract including various pterilae which is located on the wing. Thumb is the rest of the second finger. While the feathers that cover the upper and lower surface of the wing are called the covert and the feathers on the axial wing are called axillary.
Femoral tract, hair that extends along the outer surface of the thigh near the knee joint to the body.
Crural tract, feathers that make up the rest of the other feather fields in the legs (Sukiya, 2003).

Substitution of Fur
Bird feathers are formed from non-living structures so they are easily wrinkled due to oxidation and friction. Old feathers will periodically come off and be replaced by new feathers. The release and replacement of these feathers is called molting. Substitution of hair occurs at certain times of the year and completed in one period (for several weeks).

Generally birds change their feathers once a year, but female hummingbirds experience feather changes once in two years. Feather replacement usually occurs before or after breeding. But there are also those who have partial hair changes due to certain reasons. Substitution of bird feathers is influenced by many factors, including physiological factors namely the presence of the hormone thyroxine.
The perfect feathers of every bird species from hatch to adult vary. There are several species of birds which hatch bare / don't have feathers. At the time of hatching feathers is called Christmas plumage.

Most bird species have varying amounts of feathers when hatching, only a few feathers in altrical species (for example pigeons) or whole bodies covered in feathers in young precocial birds (eg chickens). When you hatch, the hair will fall out and be replaced with a new one, as follows:
Juvenalplumage (plumage), more substantial than Christmas plumage. Passerines only lasted a few weeks ago and fell first winter plumage feathers.
First winter plumage (feathers when one year old), obtained in late summer or autumn and lasts for 12 months, depending on the species.
First nuptial plumage (first mating feathers), the first breeding feathers that will fall out as a result of hair replacement after the first mating period.
Second winter plumage (second year fur), can be distinguished from adult fur in winter except for species that obtain adult fur in the first year or more than two years. This fur will be replaced by the second mating feather the following spring.