Public asked to take part in abnormal plumage survey
Changes in pigmentation can cause some blackbirds to have all-white feathers.
Members of the public are being asked to record any birds they spot with unusual plumage, such as a blackbird or sparrow with white feathers.
The reports will help the British Trust for Ornithology (BTO) to map sightings as it works to better understand the phenomenon. It has been conducting a survey on abnormal plumage since 2011.
Plumage abnormalities can range from birds having a few feathers paler or darker than usual to birds that are fully albino.
Although it can be caused by unusual feather growth or loss, abnormal plumage is most commonly caused by changes in the amount or distribution of feather pigments. Blackbirds, for example, sometimes have white patches caused by a lack of the dark pigment melanin, a condition known as leucism.
Reduction in pigment can cause more than a change in colour. It can also mean that feathers are weaker, making them more vulnerable to wear and tear, and can reduce their insulating qualities.
A complete lack of melanin can result in fully albino birds with all-white feathers and pink eyes. Such birds have associated issues with their eyesight and rarely survive to be adults.
Other problems with pigmentation include melanism, where there is too much dark pigment, erythrism, where there is too much chestnut-red pigment, and xanthochromism, where there is too much yellow pigment.
Santiago Cárdenas, Garden BirdWatch Survey organiser, said: “Since we launched the Abnormal Plumage Survey in 2011, we have received thousands of records.
“Blackbirds have, so far, been the real stars of the show, with many of the reports relating to this common garden species. However, many other birds, sporting a wide range of plumage abnormalities, have also been spotted.
“We still have a lot to learn about the distribution of such unusual birds, and we welcome all records from garden birdwatchers across the UK.”
Anyone wishing to report a sighting can do so on the BTO website.
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