Bird louse refers to any chewing louse

Chewing louse

Mallophaga is a suborder of lice, known as chewing lice, biting lice or bird lice, containing more than 3000 species. They have paurometabolis or incomplete metamorphosis....

 (small, biting insects) of order Phthiraptera which parasitizes warm-blooded animals, especially bird

Bird

Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s. Bird lice may feed on feather

Feather

Feathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They...

s, skin

Skin

-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...

, or blood

Blood

Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

. They have no wings, and ther biting mouth parts distinguish them from true lice, which suck blood.
Almost all domestic birds are hosts for at least one species of bird louse. Chickens and other poultry are attacked by many kinds of bird lice. Bird lice usually do not cause much harm to a bird unless it is unusually infested as in the case of birds with damaged bills which cannot preen themselves properly. In such cases,their irritation may cause the bird to damage itself by scratching. In extreme cases, the infestation may even interfere with egg production and the fattening of poultry. Unlike true lice, bird lice do not carry infectious diseases. Having coevolved

Host-parasite coevolution

Host–parasite coevolution is a special case of coevolution, which is defined as the reciprocal adaptive genetic change of two antagonists through reciprocal selective pressures...

 with their specific host(s), phylogenetic relationships among bird lice are sometimes of use when trying to determine phylogenetic relationships among birds.

Earlier all chewing lice were considered to form the paraphyletic order Mallophaga while the sucking lice were thought to consider the order Anoplura. Recent reclassification (Clay, 1970) has combined these orders into the order Phthiraptera. The bird lice belong to two suborders, Amblycera

Amblycera

The Amblycera are a large suborder of chewing lice, parasitic on both birds and mammals. The Amblycera are considered the most primitive suborder of lice.-Description:...

 and Ischnocera

Ischnocera

The Ischnocera is a large suborder of lice mostly parasitic on birds but including a large family parasitic on mammals. The genus Trichophilopterus is also found on mammals but probably belongs to the "avian Ischnocera" and represents a host switch from birds to mammals...

, although some members of these suborders do not parasitize birds and are therefore not bird lice.

The families which parasitize birds are :

• Suborder Amblycera
  • Family Menoponidae
    Menoponidae
    Sometimes referred to as the chicken body louse family, the Menoponidae are a family of a larger group Amblycera of the chewing lice. Most commonly they are ectoparasites of a wide range of birds....
    
     - birds, especially poultry.
  • Family Laemobothriidae
    Laemobothriidae
    The Laemobothriidae are a family of a larger group Amblycera of the chewing lice. Most commonly they are ectoparasites of birds. The genera are sometimes all united in Laemobothrion....
    
     - water birds and hawks.
  • Family Ricinidae - hummingbird
    Hummingbird
    Hummingbirds are birds that comprise the family Trochilidae. They are among the smallest of birds, most species measuring in the 7.5–13 cm range. Indeed, the smallest extant bird species is a hummingbird, the 5-cm Bee Hummingbird. They can hover in mid-air by rapidly flapping their wings...
    
    s and passerine
    Passerine
    A passerine is a bird of the order Passeriformes, which includes more than half of all bird species. Sometimes known as perching birds or, less accurately, as songbirds, the passerines form one of the most diverse terrestrial vertebrate orders: with over 5,000 identified species, it has roughly...
    
    s.
• Suborder Ischnocera
  • Family Philopteridae
    Philopteridae
    The Philopteridae are a family of Ischnocera, chewing lice mostly parasitic on birds.The taxonomy and systematics of the group are in need of revision; the Philopteridae are almost certainly paraphyletic.-Selected genera:...
    
    - birds, especially poultry.