Bird Leucism

bird leucism

What is Bird Leucism

Bird Leucism: Is a genetic mutation that results in a total or partial reduction of color in a bird’s plumage. The reduction of color in the bird’s plumage is due to an inadequate deposition or fixation of pigments only in the bird’s feathers. Other parts of the bird’s body have normal coloration.

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A leucistic bird has the pigments or normal amount of melanin. It is just that such pigments are inadequately fixated or fail to be deposited properly in the feathers. This means that leucistic birds have a normal coloration of the eyes, bill, legs, and bare parts.

Do all Leucistic Birds look alike?

No, the mutation itself happens in varying degrees, which results in different levels of leucism. Some birds show plumages that are only a washout of the original plumage, others show only patches of white, a few white or pale feathers, while others are completely white.

Interestingly, some leucistic birds show minor variations in the amount of white on their plumage over time. The amount of white may increases or decreases with a new mold of the plumage. Leucistic birds kept in captivity have been known to vary back and forth on the amount of white or pale feathers in their plumage.

Read more about Bird Albinism.

albino and leucistic birds

What is the Difference Between Leucism and Albinism

  Albinism Leucism
A mutation that results in: Total lack of melanin Loss of pigmentation only
in the feathers
Plumage coloration: Always pure white Vary from a washout of
the normal   plumage, a
few white feathers, 
to
pure white
Color of other parts of the  body: Eyes are pink or reddish; other bare parts are pale
without color
Eyes, bill, and bare parts
are of the normal color

Do you have examples of the various degrees of leucism in Birds?

While an example for each type of leucism is impossible because each mutation is unique and result in a unique and different plumage, leucistic birds can be separated into three broad categories:

leucistic birds
Three leucistic birds with different degrees of leucism. Pure white: Great Thrush (Turdus fuscater); washout of the normal plumage: Turkey Vulture (Cathartes aura),  and scattered feathers in plumage: Smooth-billed Ani (Crotophaga ani).

Do leucistic birds have problems with having different plumages?

Depending on the extent of leucism or how much they differ from the normal plumages birds may face:

  • An Increased Risk of Predation: Most birds rely on their plumage to blend in the habitat they use. Predators, particularly hawks and falcons, are quick to identify a bird that looks different and will attempt to prey upon it more often than normal. Peregrine falcons that attacked flocks of racing pigeon targeted white or partly white pigeons for singling out of the flock and further pursue more often than they did normal or dark-colored pigeons.
  • Plumage Deterioration: Melanin, a dark pigment, is an important structural component of a feather. The lack of melanin results in a plumage not as firmly cohesive as a typical plumage and feathers that wear down faster than normal colored ones, particularly flight feathers. Leucistic birds may require to spend more energy to thermo-regulate their bodies and activities that involve flight.
  • Inability to Find Suitable partners: In some birds, plumage and feathers of the body play an important role in courtship display. It is likely that not having the right plumage coloration makes leucistic birds not recognizable by potential mates. However, a leucistic plumage on the mating success of a leucistic individual has not been tested.

Related: Bird Plumage: Pattern & Functions

leucistic plumage
A pair composed of a leucistic and normal plumaged, apparently mated, Rufous-collared Sparrows (Zonotrichia capensis).

How to Identify Leucistic Birds?

Seeing a leucistic bird in a place where such plumage is unexpected is sure to call an observer’s attention. At first, such plumage may bring confusion, but at a closer look, you will likely be able to arrive at the correct bird identity.

Most leucistic birds have washed-out versions of the typical plumage, have only blotches of white or white feathers throughout the entire plumage. Identifying these birds is relatively easy despite their unusual plumage.

Related: A Guide to Bird Feathers

 

bird leucism
Leucistic Mourning Sierra-Finch (Phygilus fruticeti) showing the dark eyes, orange bill, and legs similar to the birds that accompany it.

Pure white leucistic birds are relatively rare. To identify them:

  1. See the other birds that are associated with the leucistic bird. Since the bill, eyes, and legs color in leucistic birds are normal, compare them to the other birds’ bare parts.
  2. If the Leucistic bird is alone, you would need to have one or more potential candidates based on the bird’s appearance. Then, check the habitat type, size, shape, and behavior to confirm the bird’s identity. 

Conclusion:

Leucism in birds is overall rare but relatively more common than albinism. Leucistic birds show a variable amount of white or pale in the plumage. The eyes, bill, and other bare parts are of the normal color.

Birders rely on plumage as the primary clue for bird identification. An atypical bird plumage is likely to cause a temporary confusion. Still, taking the clues suggested here, it is likely that you will be able to arrive at the correct bird identification.

Also, see Bird Melanism.

References:


  • Coat colour, dominant white at Online Mendelian Inheritance in Animals.
  • Johnson, Thomas (14 September 2017). “Rare white giraffes spotted in Kenya.” Washington Post. Retrieved 31 December 2017.

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