Many birders enjoy lifelong hobbies relying birds’ plumage alone to distinguish the hundreds of different species on their life lists, but not all birds have predictable plumage and conditions such as bird leucism can make identification more of a challenge.
What is Leucism
Leucism, or leukism, is an abnormal plumage condition caused by a genetic mutation that prevents pigment, particularly melanin, from being properly deposited on a bird’s feathers. As a result, the birds do not have the normal, classic plumage colors listed in field guides, and instead the plumage have several color changes, including:
- White patches where the bird should not have any
- Paler overall plumage that looks faint, diluted or bleached
- Overall white plumage with little or no color discernable
The degree of leucism, including the brightness of the white and the extent of pigment loss, will vary depending on the bird’s genetic makeup. Birds that show only white patches or sections of leucistic feathers – often in symmetrical patterns – are often called pied or piebald birds, while birds with fully white plumage are referred to as leucistic birds.
Leucistic and Albino Birds
Albinism is another genetic condition that can turn a bird’s plumage pale, but there are distinct differences between albino and leucistic birds. Leucism affects only the bird’s feathers, and typically only those with melanin pigment – usually dark feathers. A leucistic bird with different colors may show some colors brightly, especially red, orange or yellow, while feathers that should be brown or black are instead pale or white. Some leucistic birds, however, can lose all the pigment in their feathers and may appear pure white.
Albinism, on the other hand, affects all the pigments, and albino birds show no color whatsoever in their feathers. Furthermore, an albino mutation also affects the bird’s other pigments in the skin and eyes, and albino birds show pale pink or reddish eyes, legs, feet and a pale bill, while leucistic birds often have normally colored eyes, legs, feet and bills.
How to Identify Leucistic Birds
While leucistic birds will show irregular plumage coloration, it is still possible to identify the birds easily. Many birds with leucism still show a faint wash of color in recognizable patterns on their feathers, even though the color may not be as strong as would be typical. Of course, piebald leucistic birds still show other colors and only have patches of white feathers, but their plumage can easily be used for identification aside from those feathers.
Pure white leucistic birds can be more challenging to identify. The size and shape of the bird as well as its range, feeding habits, behavior and what other birds it associates or flocks with can be clear indicators of its species. Birders who know how to bird by ear can identify birds by sounds and songs, regardless of what the bird’s plumage may look like. If a close, detailed view of the bird is possible, identification may be able to be made from the patterning of the feathers and their orientation in different sections of plumage – sections that would normally be different colors.
Problems With Bird Leucism
While leucism can be unusual and exciting for a birder to see, birds with the condition face special challenges in the wild. Lighter plumage may rob the birds of protective camouflage and make them more vulnerable to predators such as hawks and feral cats. Because plumage colors play an important role in courtship rituals, birds with leucism may be unable to find strong, healthy mates. Melanin is also an important structural component of feathers, and birds with extensive leucism have weaker feathers that will wear out more swiftly, making flight more difficult and eliminating some of the bird’s insulation against harsh weather. White feathers also reflect heat more efficiently, which can be fatal for birds that rely on sunbathing and solar radiation for heat in northern climates.
Because so many birders rely on plumage colors and patterns for bird identification, seeing an unusual bird with lighter colors or white patches can initially be confusing. By understanding what leucism is and how it can affect birds, birders can better appreciate the great variety of avian life they see.
Photo – Leucistic American Crow © Dominic Sherony