Every now and then the keen observer of garden birds will turn up something odd. For most of us this won’t be a rare species new to the British List, instead we are most likely to be visited by a common species with a plumage aberration or other anomaly. These differences can range from albino individuals, fully white with pink eyes and bare parts, to conditions that involve feather pigmentation such as melanism (darker feathers) and leucism (paler feathers). Often these individuals are very striking, they can cause identification confusion if observers are not familiar with the size, shape and behaviour of the species involved.
Conditions such as leucism can result in just a single feather or a few individual feathers becoming white. It’s thought to be related to a poor diet. These white feathers can make the individual birds stand out from the crowd. Whilst that may not always be a good thing in a world where predation is an ever-present threat it can mean that you can track an individual bird in your garden over several years. My garden feeders attracted a female House Sparrow with one or two white covert feathers in the wings over a three year period. This year an adult Starling with a single white tail feather has visited on a few occasions over the winter, it’ll be interesting to see if it returns next winter.
One of my neighbours a few streets away is a photographer and has a good garden feeding setup. Tom and I frequently get visits by the same birds and he occasionally sends me images of some of the more unusual species he gets such as Willow Tit and Mealy Redpoll to see if they are visiting my feeders too. We share birds so to speak as our gardens are only a few hundred metres apart.
This week he sent me some very pictures of a very unusual Blue Tit, not an individual I have seen in my garden (yet). Tom has kindly allowed me to share them on this blog.
This Blue Tit has a condition known as Avian Keratin Disorder (AKD), this condition results in overgrown or deformed beaks. Scientists are still investigating the causes of this condition though it may be related to a virus. AKD certainly causes the small number of birds who suffer from it to stand out with big overgrowths, generally of the top mandible.
Unfortunately it’s likely that those individuals who do suffer from the condition will have lower lifespans as it can make feeding difficult.
Blue Tit photography by Tom Quenent
Our Garden Birder’s Diary is written by Northumberland-based birder Alan Tilmouth who has been birdwatching for over 30 years and writing about birds in various guises for the last decade. A keen garden birdwatcher, he also manages to unearth the odd rare bird on his travels. You can find Alan on Twitter and his Facebook blog.