Showing posts with label leucism. Show all posts
Showing posts with label leucism. Show all posts

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.

Friday, December 5, 2014

Birding Friday Fun

Following a spot of bird ringing inland on Wednesday it was good to go birding along the familiar coast today. However the weather wasn’t too friendly with wind and intermittent showers so there’s not a lot to report. 

I started off at Knott End for the incoming tide where the stiff north westerly made for cold hands and shaky optics. A far from complete count gave minima of 18 Eider and a single great Crested Grebe on the incoming tide. On the shore and near the jetty a mix of 1700 Oystercatcher, 700 Dunlin, 290 Redshank, 180 Knot, 145 Bar-tailed Godwit and 42 Turnstone. The jetty hugging Turnstones can be relied upon to provide a few pictures, the other species out on the shore proving much harder to approach. 

Turnstones

Knot

There was a flock of approximately 45 very flighty Twite. The birds were disturbed by a walker and then settled back down in the grassy marsh and out of sight. Two Pied Wagtails, 10 Goldfinch and 1 Rock Pipit also. 

At Damside, Pilling approximately 1800 Pink-footed Geese occupied the same fields they recently adopted. I searched through the scattered flock for the oddities that occur, the best I could find today a rather obvious partly leucistic bird. Leucism which differs from albinism is caused by a reduction in pigment of a bird’s feathers. This particular pinkie seemed to be leucistic on one side of the body only and so much more obvious when facing one way rather than the other. 

Pink-footed Goose

In the same field were approximately 120 Curlew, a couple of Oystercatchers and a single Black-tailed Godwit. 

Black-tailed Godwit

I parked up at Fluke Hall and walked the wood and shore circuit. Through the wood a Nuthatch called and a Jay shrieked off as I interrupted its feeding time. Along the shore, 12+ Little Egrets, 6 Whooper Swan, more Curlews, 140+ Shelduck, a Rock Pipit and a Stoat, Mustela ermine.

The Stoat was in an area where lots of Red-legged Partridge hang around. There’s no doubt a wily Stoat will help itself to more than a few of the shooters’ partridges in the course of the winter months. 

Stoat

The human race often interferes with the natural world without fully studying the possible or likely consequences. In the 19th century, Stoats were introduced into New Zealand to control rabbits but the Stoats had a devastating effect on native bird populations. New Zealand has a high proportion of ground-nesting and flightless birds, due to the long geographical isolation and the lack of natural mammal predators. The introduced Stoats took full advantage of the bounty. 

That’s all for today. Look in soon for more birds, birding and other tales from Another Bird Blog.

Linking today to Anni's Blog and Eileen's Saturday.

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