How Oil affects Birds
When oil sticks to a bird's feathers, it causes them to mat and separate, impairing waterproofing and exposing the animal's sensitive skin to extremes in temperature. This can result in hypothermia, meaning the bird becomes cold, or hyperthermia, which results in overheating. Instinctively, the bird tries to get the oil off its feathers by preening, which results in the animal ingesting the oil and causing severe damage to its internal organs. In this emergency situation, the focus on preening overrides all other natural behaviors; including evading predators and feeding, making the bird vulnerable to secondary health problems such as severe weight loss, anemia and dehydration. Many oil-soaked birds lose their buoyancy and beach themselves in their attempt to escape the cold water. The fortunate ones are taken in by concerned citizens or capture crews.
Bird feathers are naturally waterproof, but to maintain this, each feather must be aligned properly so that water cannot seep through the microscopic barbs and barbules that are part of the vane of each feather. These barbs and barbules hook together like Velcro to form a tight waterproof barrier. Each properly aligned feather overlaps another like the shingles on a roof to create an entire waterproof covering for the bird. It is the bird's job to maintain its feather structure. While preening, birds distribute natural oils, which help in the long-term maintenance of feathers by keeping the feathers supple so alignment can be maintained.
Properly aligned feathers will not allow water or air to penetrate and ensure that the bird is buoyant and insulated from the cold. Every day birds spend considerable time preening because if their feathers are not perfectly aligned, it could kill them.