There are many types of lice, so check all of the places that the species of lice live. I always check vent, legs, wings, neck, chest, and head.
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Main species of lice on domestic birds
Cuclotogaster heterographa, the
head louse, is about 2.5 mm long and is found mainly on the head and the neck of birds. It prefers to stay close to the skin or at the base of the feathers. It does not suck blood, but feeds on skin and feather debris. It is more frequent on young birds and turkeys. Heavy infested birds may even die before maturity.
Eomenacanthus stramineus (=
Menacanthus stramineus), the
chicken body louse is the most common species on domestic birds, and probably the most damaging one. It is rather large (2.5 to 3.5 mm long) and of a brownish color. It feeds mainly on feather debris, but is capable of sucking blood. It lives mostly on the skin of birds, seldom on the feathers, and prefers body parts with few feathers, e.g. around the vent, although in case of heavy infestations it may be found also on the head, under the wings and on the chest. The eggs are laid in clusters on the feathers or directly on the kin.
Goniocotes gallinae, the
fluff louse, is one of the smallest lice of poultry, only 0.8 to 1.5 mm long. It is found all over the birds' body, but less densely on the head and the wings, on the fluff or base of the feathers. It also feeds mainly on feather debris.
Lipeurus caponis, the
wing louse, is 2.0 to 2.5 mm long, and has a grayish color. It is found mainly in the inner part of wing, tail and head feathers. It only feeds on parts of the feathers, but so intensively, that is also called the
depluming louse.
Menopon gallinae, the
shaft louse, is rather small (1.5 to 2.0 mm long). It feeds mainly on skin and feather debris, but may also suck blood from the wounds it produces. It prefers the chest, the shoulders and the back of birds. Eggs are whitish and are laid often in clusters at the base of the feathers.
Columbicola columbae, the
slender pigeon louse, is 2.0 to 2.8 mm long. It can be found all over the body, especially at the inner side of the wing feathers. It feeds on feather debris. Eggs are laid preferentially are the small feathers under the wings.
Source:
https://parasitipedia.net/index.php?option=com_content&view=article&id=2655&Itemid=2933