The other day I was sent an email with an attached photograph of a bird seen on Kauai, the most westerly of the main Hawaiian Islands. The photographer was Donald Thornton, a Californian on holiday on Kauai, who told me that he and his wife had been taking bird pictures in Spouting Horn Park near Poipu and come across something they just couldn’t identify. Could I put a name to it, Don asked?

I’ve never been to Hawaii and don’t know all that much about Hawaiian birds consequently, but like (I suspect) most birders I do know that there are some unique and difficult to identify birds on the Islands. As the photo downloaded I have to admit I was feeling very curious to know if I had any chance at all of putting a name to it.

As it turned out I was able to identify the bird in the photo - which is posted below - fairly quickly. Have a look and see what you think it is yourselves…

When I said I could identify the bird fairly quickly, I meant absolutely no disrespect to Don at all (and I asked his permission before writing this post which he happily gave me incidentally). I can completely understand why he had been stumped: he was in an unfamiliar region full of unfamiliar birds, faced with a bird that didn’t quite ‘fit’ - whereas I was able to step back and recognise that what he had photographed was a bird I get in my own garden at home, and in a ‘plumage state’ that I’d actually seen before.

The bird is - and did you get this right? - a leucistic House Sparrow Passer domesticus.

Leucistic? Leucism is a fairly unusual condition where the pigmentation cells in a bird (or any other animal) fail to develop properly. The result is a scattering of abnormally coloured (usually ‘non-coloured’) feathers, which show as white patches or white blobs randomly scattered throughout the plumage.

The clue that you’re looking at a leucistic bird is in that word ‘random’. There are sparrow-like birds with white heads (the African White-headed Buffalo Weaver for example), but there are none where the white is arranged asymmetrically or dotted with random areas of ‘normal’ colour.

Looking again at Don’s sparrow there are clearly brown spots on the crown, a wash of very pale brown tones below the eye, and even though the whole bird can’t be seen the white on the back doesn’t look even, and the white in the upperwing isn’t arranged or confined by or to feather tracts but look to be random also.

On top of that everything about this bird suggests a House Sparrow (which Don did consider). It’s the right shape, size, and structure and is in the right habitat. Aside from the white patches the rest of the plumage is spot-on for a House Sparrow. And - as a look on the internet reveals - sparrows were introduced to the Hawaiian Islands in 1871 (I’m not sure why, but the usual ‘reason’ for introduction of this species was for insect control) and have been doing well ever since.

Interestingly a good friend of mine, Jack Cole, has sent me a photo (posted below) of a similar female House Sparrow that he found on another Hawaiian island, Maui, in December 2008.

Leucistic House Sparrow, Maui. Copyright Jack Cole

Had I been in Don’s place would I have just thought to myself, “leucistic House Sparrow” and walked on. I doubt it very much. As I said I don’t know very much about Hawaii’s birds and my first instinct (and fervent hope) would be that I’d found something remarkable and endemic, a lifer that I might never see again…I’d have been wrong but it’s worth bearing in mind, in other words, just how much our expectations are built up by birding in a new and exotic location!

Having travelled so widely now, though, and come across leucistic ducks, crows, American Blackbirds, Fox Sparrows, and even a Cactus Wren in the past I think I would have soon experienced that familiar ’sinking feeling’ and realised what it was I was looking at…

Leucistic American Robin, Illinois. Copyright Charlie Moores

Leucistic Cactus Wren, Arizona. Copyright Charlie Moores

Don’s photo does bring up another interesting question though: what’s the difference between ‘leucism’ and ‘albinism’?

Many birders, myself included, would probably happily describe Don’s sparrow as a ‘partial albino’ - but, speaking in a strictly scientific sense, we’d be wrong. Simply put, albinism is a genetic aberration involving recessive genes 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.

So what is ‘leucism’ therefore? Scientists and aviculturalists use the term slightly differently, but in essence (as I understand it) ‘leucism’ is a genetic defect where some pigmentation cells are unevenly distributed causing uneven distribution of colour or where the cells are faulty which causes a partial loss of pigment which can affect all of the colours that should be present in those feathers and ‘dilute’ their intensity, or cause asymmetric and randomly-arranged patches of white feathers. In a leucistic bird some/most of the ‘normal’ colours and associated plumage marks are typically still present, therefore, and in many cases the soft parts - the bill, legs etc - will also be largely normally coloured (though as the images here shows that’s not always the case by any means).

For an interesting example of a leucistic House Crow and an amusing discussion have a look at Daisy O’Neill’s post on the excellent Bird Ecology Study Group website (and my thanks to Daisy for allowing me to reproduce one of her photos below, and to YC Wee for acting as go-between!).

Leucistic House Crow, Penang, Malasia. Copyright Daisy O’Neill