Saturday, August 18, 2018

A Whiter Shade Of Pale

The week has been a frustrating one of dull days, bouts of rain and irritating wind speeds that preclude even an hour or two of ringing. Consequently I've not done a lot of anything birdy wise. 

During the dry spell of June and July the garden was devoid of birds apart from a few Goldfinch, the usual Woodpigeons and a passing Great-spotted Woodpecker. Last night when dozing half asleep I heard the screech of a Tawny Owl that sounded very close, probably in our apple tree. It’s about now that Tawny Owls start to sort out their winter territories as a prelude to their often post-Christmas breeding and each year and there’s always a pair in the trees just along the road from here. 

Tawny Owl 

But in the last few weeks, and with the change of season, lots of Goldfinch reappeared on the feeders in some numbers. These birds are about 90% juveniles and probably the second or even third brood of their productive parents. Yesterday I counted up to 20 Goldfinch at a time on the feeders, so goodness knows how many individuals that represents using the garden during the course of a day. 

So when Sue went off shopping to the big city, I was left home alone with just a mist net for company and where the breeze was not a major problem in the sheltered back garden. I caught just Goldfinches and no other species, exactly as expected where Goldfinches are by far the most common bird in our semi-rural location. 

What I didn't anticipate was to catch a very leucistic Goldfinch. It was one born this year. With its washed out appearance and lack of pigmentation I sexed it as male by a combination its long bill, the lengthy wing and healthy weight. I didn't see or catch any similar birds so there is no way of knowing if this was a one off, if there are similarly affected siblings or whether it inherited the leucism from a parent.  

Leucistic Goldfinch 

Leucistic Goldfinch

'Normal' Goldfinch

Here’s a little more about leucism & albinism in birds. From the British Trust for Ornitholgy (BTO). 

"Leucism is an abnormal plumage condition caused by a genetic mutation that prevents pigment, particularly melanin, from being properly deposited on a bird’s feathers. This results in white feathers, unless the normal plumage colour also comprises carotenoids (e.g. yellows), which remain unaffected by the condition. Although leucism is inherited, the extent and positioning of the white colouration can vary between adults and their young, and can also skip generations if leucistic genes are recessive. 

The reduction of pigment in leucistic birds causes feathers to weaken and be more prone to wear. In some situations this can hinder flight, which, in addition to leucistic birds usually being more conspicuous, can heighten risk of predation. There is also evidence that leucistic birds might, on occasion, not be recognised or accepted by a potential mate. 

Leucistic Goldfinch 

Leucism is an umbrella term to encompass a number of plumage irregularities that can be difficult to distinguish from each other. One of these is called ‘progressive greying’, which also results in white feathers. While leucism is heritable, progressive greying is not – but without knowing the history of a bird, these two conditions are difficult to tell apart. 

‘Dilution’ is another condition grouped under the category of ‘leucism’. Here, plumage colour often appears ‘washed out’ (i.e. ‘diluted’). In dilution, melanin cells are present (unlike in leucistic birds) but produce less pigment than normal. White feathers can also be caused by chromatophore (pigment cell) defects, rather than an absence of melanin-producing cells. 

Albinism also results in white feathers but true albinos are thought to be rare in the wild. Albinism is caused by a genetic mutation causing an absence of tyrosinase in pigment cells. An albino individual is unable to produce melanin pigments. This leads to a good diagnostic feature with which to distinguish leucistic and albino individuals – the colour of the eye. 

Leucistic Goldfinch 

Albinos have pink eyes while the iris pigmentation of leucistic birds remains dark. Most albino birds die soon after fledging, primarily as a consequence of their poor eyesight, and albino birds are not thought to progress to adulthood in the wild. As with leucistic individuals, albinos can retain carotenoid pigments if normally present in the plumage. A common misnomer is ‘partial albino’ – this is not possible since albinism affects the whole plumage of a bird, not just part." 

Because so many birders rely on plumage colours and patterns for bird identification, seeing an unusual bird with lighter colours or white patches can initially be confusing. By understanding what leucism is and how it can affect birds, birders can better appreciate the great variety of avian life they see. 

Linking this post to Anni's Birding Blog.

13 comments:

David Gascoigne said...

Good morning Phil: Leucistic birds are always interesting and can lead to misidentification, especially if the observer fails to take into account habitat and behavioural clues as to the identity of the bird. I am far from leucistic right now having just returned from a short sojourn on the Gaspé Peninsula where I had lots of exposure to sun and wind........turning me into a bronzed Adonis......no, correct that a wrinkled old man! My wife might even say a more wrinkled old man. Had a wonderful birding experience down there especially with the huge colony of Northern Gannets on Bonaventure Island. It’s about a seventeen hour drive, but it was well worth it.

eileeninmd said...

Hello, I love your tawny Owl. It is a beautiful bird. The leucistic Goldfinch is lovely, what a nice catch. Enjoy your weekend!

sandyland said...

overall throughout the years have you seen many leucistics? all types of birds??

~Lavender Dreamer~ said...

I'm always thrilled when you have a photo of an owl! It's still on my 'yet to see' list! And we have a lot of goldfinches here but not in the summer months. How interesting to see the Leucistic Goldfinch!

Rhodesia said...

I do love Owls of any kind and I am only too happy to hear them even if I do not get to see them. I have not seen a goldfinch here this year, but I am sure they will turn up when food is short!! I have seen the return of a few great tits, but the blue titis still seem to be in hiding and also the one winter robin that we see has not returned. I love the birds in winter I only wish it did not have to be so cold!!
Enjoy your Sunday, Diane

Powell River Books said...

I hear owls quite frequently, but have never had the pleasure of seeing one in the wild. - Margy

Margaret Adamson said...

great shots of the eucistic Goldfinch and for you to be able to exam it so closely. Great to see the Ow shot Phil. Have a wonderful week ahead.

Anni said...

This was incredibly educational!! But, twenty goldfinch at once? I'm lucky to see one!! That owl...sweet! - That's why they call me Hootin' Anni (my love for owls)...thanks for sharing this with us this week at I'd Rather B Birdin'

Betty Crow said...

Interesting information on the Leucistic Goldfinch. Nice shot of the owl. I looked out the window last night and saw an owl perched on the ground wire to our light. He was big and light colored, but couldn't see him good enough to identify him and too dark for my camera. Hope he comes back. It was exciting to see.

Mary Cromer said...

Such a beauty the little Leucistic Goldfinch Phil. There was a recent red Cardinal...male that had this condition near where I live, but I never went to see it. I have only seen a partially Leucistic Red-tailed Hawk and how interesting it was to see. Beautiful is the Goldfinch, really sweet looking bird. Do they have eye problems over there? Here we get a lot with an eye condition that is really very frustrating to see. Have to just keep the feeders even cleaner than normal.
Oh how adorable is the Tawny Owl. My oldest daughter got to see one while visiting at Oxford last month~

Wally Jones said...

Happy to hear your weather may be improving a bit and that migration is underway. Very interesting post on leucism. Have encountered a smattering of affected birds over the years. The most striking was a black and white Boat-tailed Grackle in the back yard. Thought for sure I had a Florida record for a Magpie!

Here's hoping your future forays take you beyond your garden, although it seems your doing quite well on studying goldfinches!

Our own migration has begun with dribs and drabs of redstarts and yellow warblers. We typically have a small flourish of activity at this time each year and then nothing until mid-September.

We hope your brand new week is filled with birds, excitement and Fun!

Angie said...

Phil - very interesting - I did not know about this genetic mutation, so I learned a lot today. And quite helpful to have a picture with a comparison to a normal goldfinch. But of course, you know I am partial to owls, so I loved the tawny owl photo!!!

italiafinlandia said...

The small Goldfinch is so tender! Thanks for your clear lesson.

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