Cactus Wren Campylorhynchus brunneicapillus
USA and Mexico. Various dates 2004/05

 

The Cactus Wren is the largest North American wren, and is 18-23 cm (7-9 inches) long. Native to the south-western United States southwards (southern California, southern Nevada, Utah, Arizona - it’s Arizona’s State bird, and western Texas) to central Mexico it is as might be expected a bird of arid regions, and is often found around yucca, mesquite or saguaro. It nests in cactus plants, sometimes in a hole in a saguaro, or where its nest will be protected by the prickly leaves of a cholla or yucca. It rarely drinks water, getting its moisture from its food (mainly insects).

Cactus Wrens form permanent pair bonds, and the pairs defend a territory where they live all through the year. There is little sexual dimorphism.

Two main groups occur: the nominate brunneicapillus is found in NW Mexico and includes couesi which ranges from SW USA, N Baja California, and northern parts of NW Mexico; and affinis which is found through the Baja peninsula (”Birds of Mexico and northern-central Mexico”, Howell and Webb).

 

Near Mexico City, Mexico, June 2004:

 

 

 

 

 

 

 

 

 

 

Joshua Tree National Park, California. June 2004:

 

 

 

 

 

 

 

Partial-albino, Papago Park (near Phoenix), Arizona. November 2005:

 

 

 

 

I sent a photo of this partial-albino to the very popular Birds-Pix Yahoo group. I had hoped that it might be interesting to its members - it was, but rather than discussing my good fortune in “right place, right time” it instead caused quite a debate over my use of the term “part albino” in the subject bar. Can you have a “part” albino?, asked one member. Surely, he means ‘leucistic’, said another…Well, yes you can, and no I didn’t: and here’s why.

Firstly, what is “albinism”? Simply put, albinism is a genetic aberration where there is a total absence of pigment in the plumage and/or bare-parts. An “albino” bird therefore is one with no pigment whatsoever: it will have totally white feathers, and it will have a pink bill and legs, and pink or red eyes, caused by the blood supply under the pigmentless skin being visible.

Secondly, what is “leucism”? Scientists and aviculturalists use the term slightly differently, but in essence “leucism” is a partial loss of pigment which affects all of the colours present and ‘dilutes’ their intensity. Colours and associated plumage marks are still present, therefore, but are washed-out.
This dilution or washed-out appearance can be caused by another aberration called “schizochroism”. Here, though, one or more specific pigments (perhaps red or green) is missing: every other pigment is present at normal levels, but where a dominant colouration is lost this can result in the bird looking abnormally “pale” (if the dominant colour was black, and the genes for creating black pigment is faulty, then the bird will have white feathers instead of black ones, but will still more than likely have normally-coloured bare parts).

 

The Cactus Wren in the photos has white patches scattered throughout its plumage, but does have normal - not ‘diluted’ or washed-out - colour in eg the folded primaries and in the retrices (tail feathers). It has no pigment in the bill or legs, but does appear to have a normally coloured eye - though because of the rich blood supply to the eye “full albinos” often appear to have dark eyes.
Clearly, this is not an “albino” and is not “leucistic”: but is it a partial albino - after all many birds have the odd white feather or feather tracts? If the bare parts had been normally coloured, then the Wren could possibly have been described as just “aberrant” (though to an unusual degree), the loss of colour in the feathers perhaps caused by illness or stress and therefore perhaps temporary: but as the bare parts are mostly pigmentless as well I do feel justified in using the term “partial albino” - in this case the loss of colour is genetically-based and permanent (ie moulted colourless feathers will always grow back white).

 

All photographs © Charlie Moores