1. Abnormal Plumage Survey
Clockwise from top left:
Blackbird: condition commonly referred to a ‘Leucism’ although more precisely in this case (and, indeed, in most cases for Blackbirds) the condition is called ‘Progressive Greying’. While leucism is heritable, progressive greying is not – but without knowing the history of a bird, these two conditions are difficult to tell apart. Progressive greying: each year when worn-out feathers are moulted, more and more white ones grow back until – if a bird lives long enough – the bird will turn completely white!
Blue Tit: this bird is ‘Melanistic’. Here, there is an elevated amount and/or distribution of dark-coloured melanin pigment. In tits, it is often the white cheek patches that are affected.
Dunnock: All-white Dunnock. This bird is ‘Leucistic’ – although it is all-white we can tell that this is not an ‘Albino’ because of the dark-coloured eye. Albinos lack the dark pigment in the eye, so these appear pink. In leucistic birds, affected plumage lacks melanin pigment due to the cells responsible for melanin production being absent. This results in a white feathers, unless the normal plumage colour also comprises carotenoids (e.g. reds, oranges, yellows – such as the red face of a Goldfinch), 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.
Note – none of these birds are albinos. Albinism is, in fact, very rare in the wild, chiefly because albinos have very poor eyesight. Albinos are completely white birds, apart from any parts of the plumage that might be coloured by caroteniods as these areas are unaffected by the albinism. There is no such thing as a ‘partial albino’!
Robin Aitken, John Harding, Andrew Cook

2. Abnormal Plumage Survey
Some more funky plumage to look at… House Sparrows
Through the survey, the plumage abnormality classifications would be as follows:
Left picture = ‘Other’
Right picture = ‘Leucism’
Ian Collier, Malcolm McGhee 2

3. Abnormal Plumage Survey
Some more funky plumage to look at… Starlings
Through the survey, the plumage abnormality classifications would be as follows:
Both pictures = ‘Leucism’
Paul Pierce, Stephen Mosley 3

4. Abnormal Plumage Survey
Some more funky plumage to look at… Robins – INCLUDES ‘SANTA ROBIN!!’
Through the survey, the plumage abnormality classifications would be as follows:
Both pictures = ‘Leucism’
Donna McGhee, Ian Wilson 4

5. Abnormal Plumage Survey
Some more funky plumage to look at… Jackdaw and Blue Tit
Through the survey, the plumage abnormality classifications would be as follows:
Both pictures = ‘Leucism’
Morgan Stephenson, Richard Winston 5

6. Abnormal Plumage Survey
Some more funky plumage to look at… even Ring-necked Parakeet and Moorhen! So far, over 50 species recorded through the project.
Through the survey, the plumage abnormality classifications would be as follows:
Both pictures = ‘Leucism’
Bob Fry, Roger Nixon 6

7. Average weekly count per garden Plumage abnormality rate (PAR)
Abnormal Plumage Survey
Species
Number of records
Average weekly count per garden
Plumage abnormality rate (PAR)
Blackbird
998
2.66
375.99
House Sparrow
224
4.94
45.34
Jackdaw
144
1.12
128.11
Carrion Crow
137
0.43
318.60
Chaffinch
100
2.94
34.01
Starling 78
3.84
20.32
Robin 65
1.22
53.24
Great Tit 55
1.81
30.39
Blue Tit 53
2.80
18.93
Goldfinch 45
2.64
17.05
Greenfinch 42
1.90
22.11
Dunnock 38
1.41
26.95
Collared Dove 33
1.70
19.41
Pheasant 27
0.26
102.29
Magpie 25
0.96
26.04
Rook 23
0.30
76.92
Great Spotted Woodpecker 16
0.35
45.71
Woodpigeon
2.23
7.17
Latest results: species affected
Table: Species for which 10 or more records of birds with abnormal plumage have been collected. ‘Average weekly count per garden’ is derived from BTO Garden BirdWatch from 2010–13. ‘Plumage abnormality rate (PAR)’ is calculated from ‘number of records’ divided by the ‘average weekly count per garden’.
Of the near 2400 records submitted so far, 87.5% have been classed as being ‘leucistic’; compared with just 3.5% as ‘albinistic’; 4% as ‘melanistic’; and 5% as ‘other’.
Of all the species recorded, abnormal Blackbirds have been seen most frequently, accounting for over 40% of records. Most of these birds have sported odd white feathers or have been completely white. House Sparrows, with 224 records submitted to date, are the next most frequently seen species through the Abnormal Plumage Survey, with Jackdaw (144) and Carrion Crow (137) next on the list.
There is a bias to consider in our sample, however, given that some species are much more frequent garden visitors than others. To try and account for this, we can incorporate data from our year-round GBW survey. By dividing the number of records of abnormal-looking birds by the average weekly count for each species, the latter as documented through Garden BirdWatch, a ‘plumage abnormality rate (PAR)’ can be derived (see table).
Despite being common garden visitors, the PAR of Blackbirds still exceeds that of other species. However, several other birds – those that are less numerous in gardens but have been logged quite often through the Abnormal Plumage Survey – shoot up the table. Carrion Crows, Rooks and Robins are notable examples, while House Sparrows, which are relatively abundant in gardens, drop down the list.
The four species with the highest PARs – Blackbirds, Carrion Crows, Jackdaws and Rooks – have one particularly obvious shared characteristic: their normal plumage is a largely uniform, dark colour. Given that the most frequent plumage abnormality type recorded through the survey has been ‘leucism’, whereby unusual white feathers appear, few species could display this abnormality more clearly. However, at this stage we cannot exclude the possibility that these species might somehow be more susceptible to plumage pigmentation loss.
It’s not just strange white feathers that have been documented through the Abnormal Plumage Survey. Of the 98 records of ‘melanistic’ birds – whereby unusual dark pigmentation patterns have been seen – about 40% have been of Great Tits (26) and Blue Tits (14), with 16 other species also logged. In the case of Great and Blue Tits, it is often the case that the white cheeks or yellow bellies appear as a much darker colour.
Other fascinating abnormalities have included a family of four chocolate-brown Jackdaws in County Antrim, a Greenfinch with orange feathers in the West Midlands and a Goldfinch with an orange rather than a red face in East Sussex. On a handful of occasions, individuals have looked so unusual that participants have had to resign themselves to writing ‘species unknown’.
Dennis Simpkin, Brian Buffery, Mary Payne, Finlay Dowell 7

8. WE WANT YOUR RECORDS!!
We want your records! Please pick up an Abnormal Plumage Survey form if you have ever seen a bird with unusual plumage in your garden.
Anne Riley
Bob Fry, Roger Nixon 8