Preening

Preening is how birds use their beaks to keep their feathers in good condition. They realign feathers, reconnect separated barbules, clean their plumage, and manage parasites. Since feathers are essential for insulation, waterproofing, and flight, birds depend on them to survive. That’s why they devote a large part of each day to feather care, mostly through preening.

The behavior includes several actions. Birds fluff and shake their feathers to help rehook barbules that have come apart. They collect preen oil from a gland near the base of the tail and spread it through their feathers using their beaks. They also draw each contour feather through their bill, nibbling from the base to the tip.

Over time, some preening actions have taken on secondary roles. Ritualized preening appears in certain courtship displays. It can also serve as a displacement activity when a bird faces two conflicting urges. Though usually done alone, preening can be social, involving two or more birds—this is called allopreening. It typically happens between mates or among flock members in social species. Allopreening may help with effective grooming, recognizing individuals like mates or potential partners, or reducing or redirecting aggression in social groups. Most allopreening focuses on the head and neck, with less attention to other body parts.

Preening can cause problems if birds ingest pollutants or disease-causing organisms, leading to issues like liver and kidney damage, pneumonia, or disease spread. Injury, infection, or being caged with a dominant or aggressive cage mate can lead to overpreening in captive birds.

The word “preen” for tidying feathers comes from Late Middle English. It seems to be a variant of “prune,” which once meant “anoint,” from the Latin *ungere* (to anoint). This combined with a Scottish and northern English dialect word “preen” meaning “pierce” or “pin,” referring to the bird’s beak pricking during preening.

Preening is an innate behavior in birds, but it also has a learned component. Hand-reared birds without a role model develop abnormal preening habits. Despite spending much time trying, they don’t use proper techniques and may groom poorly. Displaced feathers can cause trouble—they may get damaged, disrupt smooth airflow during flight, or let body heat escape. Preening lets birds reposition these feathers.