Are We Seeing More Birds with Leucism?

• Last year I saw a red-winged blackbird with leucism.

• A month after that I saw a common grackle that might have leucism.

• Last month, I saw two red-winged blackbirds with leucism. They were very different looking birds because the feathers on the wings of one bird were faded, and the other was pied meaning it had white feather patches.

Leucism is a genetic mutation that causes white patches or faded color by preventing melanin from being sent to some of the bird’s feathers. This is different from albinism when birds don’t produce any melanin.

One year, four birds with leucism in my 1/4 acre rewilded yard! It's fairly easy to spot them because they stand out from other birds.

Leucism is a rare condition affecting only 1 in 30,000 birds - the Cornell Lab of Ornithology’s Project Feeder Watch noted less than 1,000 observations of individuals with leucism (and albinism) out of 30 million birds from 2000 to 2006. This is the number most often used when describing the prevalence of leucism in birds, and it hasn't been updated. Blackbirds are most affected by leucism based on multiple observational sources. It’s possible that other birds are undercounted because white feathers in birds with naturally light or white feathers don’t stand out as much as they do in blackbirds.

It might be harder to see extra white feathers from leucism in a Northern Mockingbird because they already have white feathers.

Note - I'm focusing on leucism because I've never seen an albino bird. Even though most of the studies don't differentiate between leucism and albinism for a number of reasons, albinism is even rarer than leucism. In a British Trust of Ornithology survey, 82 out of every 100 birds with abnormal plumage spotted were leucistic and only 3 were albinistic. (From this information and the Project Feeder Watch numbers it appears that if a tinier percentage of the 1 in 30,000 birds with abnormal plumage are albino, then seeing an albino bird is like winning the lottery)

This albino crow photo from Mark Hope for the Avianreport.com shows the lack of pigment in the eyes, beak, and feet which is different from birds with leucism where only the feathers are affected.

A complex combination of factors keeps leucism low in bird populations. Birds with leucism are at a disadvantage because the affected feathers are weaker and more prone to wear, more visible to predators, and might affect mating although the actual predation risk and mating impact is not clear. Birds with leucism are also smaller in body mass and size than birds without leucism.

When I saw this bird alone in a pine tree near my yard I thought he was a new bird I'd never seen until I realized he was part of a visiting red-winged blackbird flock and looked different because he has leucism.

I couldn’t find any confirmation about the phenomenon, but anecdotally, birders and naturalist are starting to comment that they’re seeing more birds with leucism, not less. The Florida Bluebirds Society questions whether external human related factors such as pesticides might be increasing the mutations or whether there are more sightings because there are more birdwatchers. Other source have noticed increases in leucism in specific bird populations associated with pollution - such as an abnormally large number of eared grebes with leucism at a State Park in Utah in 2017. A lot has changed in the last 20 years including the ubiquitous use of phones to capture images. I'm guessing this might also have something to with the increased sighting of birds with leucism.

If I didn't see hundreds of blackbirds in my small, urban yard every day, I wouldn't recognize how different this red-winged blackbird with leucism is. Red-winged blackbirds don't have white feathers or what looks like ombre wings!

Leucism can be caused by genetics, injury, aging, and environmental factors. The connection between leucism (and albinism) and environmental radiation were documented in follow-up studies of barn swallows near the Chernobyl nuclear power plant meltdown in 1986. The swallows near Chernobyl showed up to a tenfold increase in leucism (and albinism) over control groups of barn swallows. Other evidence shows pesticide exposure in birds promotes leucism.

It's rare, but sometimes if there is some kind of injury and a bird loses feathers, the ones that grow back in are white and when they molt again the feathers that come back will be the right color. One of the common grackles in this photo has a slight white spot on his tail feathers - it's hard to know if it's from injury or leucism.

Living in a city has something to do with why I may be seeing birds with leucism - there are more birds with leucism in urban areas. The reasons could be related to more leucism in males and older birds and there being more males and older birds in urban areas than non-urban areas.  Increased leucism citing in cities are not completely understood but is possibly related to anthropogenic environmental mutagens (human related contaminants) that cause genetic mutations. These mutagens are higher in urban areas and studies have shown that there are more birds with leucism in areas with high levels of mutagens.

It's hard to see because I wasn't quick enough getting a clear photo, but if you look closer where there is a solid white line in this image you can see its a feather on a female red-winged blackbird with leucism. Females are predated on more than males so there are fewer females seen with leucism.

It’s not clear yet whether there is an increase in leucism, and it seems there are still so many variables and unknowns. All I know is I’ve seen at least three red-winged blackbirds with leucism this year in addition to a grackle with possible leucism. If the chance of seeing one bird with leucism is still about 1 in 30,000 birds something is a bit wonky because I've beaten the odds by a wide margin! The environmental connection and possible increase in leucism is an area I hope is being explored because our world is getting more toxic every day. If you see a bird with leucism, you can help the general scientific community by posting it on iNaturalist or Ebird. Pesticide use is one of the leading causes of the 30% bird decline in the last 50 years, so it’s not out of the question to think there might be a link to pesticides and genetic mutations such as leucism.

Leucism is a fascinating phenomenon - but not necessarily one we want to see more of!

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