pollutants, such as leaking petroleum, they can quickly lose the preen oil from their feathers. This causes a loss of heat regulation and waterproofing, and rapidly leads to the bird becoming chilled. If waterbirds are exposed, they can lose both buoyancy and the ability to fly; this means they must swim constantly to stay warm and afloat (if they cannot reach land), and eventually die of exhaustion. While preening in an effort to clean themselves, they may ingest harmfully large amounts of the petroleum. Ingested oil can cause pneumonia, as well as liver and kidney damage. Studies done with black guillemots showed that even small amounts of ingested oil caused the birds physiological distress. It interfered with the foraging efficiency of adults and decreased the growth rates of young birds. Allopreening may facilitate disease transmission between infected and non-infected individuals. West Nile virus has been found in the feather pulp of several species of corvid, for instance, meaning that birds that preen infected partners might become infected themselves. Even preening its own body may expose a bird to pathogens. There is evidence that water-borne avian influenza virus is "captured" by the preen oil on feathers, providing a possible route for infection. The ingestion of parasites during preening may result in infection; the tick-borne disease louping ill virus can be transmitted to red grouse if the bird consumes a tick carrying the disease. Caged birds, particularly parrots, sometimes overpreen in response to being exposed to strong scents (such as nicotine or air fresheners) or as a result of neuropathy. Reducing exposure to the offending odour, or treating the underlying cause of the neuropathy (such as injury, infection, or heavy metal intoxication) can help to eliminate the behaviour. Confining a bird with an incompatible or very dominant cage mate can lead to excessive allopreening, which can result in feather plucking or injury. References Works cited External links Barred owl preening on YouTube Splendid fairy-wrens preening and allopreening on YouTube Bird behavior Feathers Hygiene Articles containing video clips