10 November 2012

Snow Buntings

Races of Snow Buntings

There are three races of Snow Bunting which can be found in Britain, though only two are regular and likely to be seen. The nominate race 'nivalis'. breeds from Canada and Greenland via Scotland to Scandinavia and NW Russia. The second race is 'insulae' which breeds in Iceland (and has been cited as a perhaps rather unlikely candidate for a split). The rarest race to appear in Britain is the NE Russian and Siberian race 'vlasowae'.

A work in progress

Because the number of Snow Buntings seen on passage and wintering in Pembrokeshire (and other west coast sites?) is small, it's difficult to be clear about the ratios of sexes, ages and races present. My own recent experience has produced rather more males of the race 'nivalis' than might perhaps have been expected since on the east coast (particularly Norfolk where there are large flocks in winter at a number of sites) trapping revealed a preponderence of females, particularly 1st year birds, of the Icelandic race 'insulae'. However I understand that the ratio of races at least may have changed significantly there in recent times, though I haven't seen any written accounts as yet. In Pembs there'll be an ongoing attempt to  photograph and, hopefully, trap wintering and passage birds.

Ageing Snow Buntings

Males, are generally whiter than females, having more extensive white on head and cheeks as well as broader white fringes to feathers on back and mantle. The white is often tipped with buff which wears over time to show more white. On the whole adult males have the whiter primary coverts and immature females the darkest but with individual variation. Also 'insulae' tends to be darker than 'nivalis'. The shape of the tail feathers is a useful method of ageing Snow Buntings with 1st year birds having more pointed and often more worn tail feathers (Svensson 1992 has useful illustrations). The tertials are often easier to see and judge and two generations of feathers; with a contrast between fresh chestnut tertials with paler more worn feathers indicating 1st year birds (usually the longest tertial is retained, juvenile). Uniform tertials and all adult type tail feathers do not always indicate an adult bird since a juvenile can, rarely, moult all these feathers.

Sexing Snow Buntings

Overall Males are whiter and more contrasting than females. Male Snow Buntings generally have more white in the wing and the primary coverts , in particular, are generally, largely white. It seems likely adults will, on the whole, show more white than 1st year birds. females have darker primary coverts and less white in the wing overall. All these features exhibit some overlap.

Racing Snow Buntings

Overall 'nivalis' is the brighter and 'insulae' the darker race, though this is subject to the criteria which determine age and sex. Males of the race 'nivalis' exhibit white rump feathers, often tipped buff or gingery buff, this often abraiding over time to become reduced. Females have the 9th primary 60% or more white (a feature often visible in photographs). Males of the race 'insulae' have black based rump feathers tipped rufous-buff. Females of this race have 40% or less of the 9th primary white. The back and mantle of 'nivalis' is often described as 'frosty' looking, having a pale greyish-white appearance. 'Insulae' is darker and browner. While this generally follows from earlier descriptions of the extent of white etc made earlier, at least one individual seen in Pembs suggests that, at the least, this feature may be worth further critical examination.

Some Snow Buntings are probably impossible to catogarise with certainty but many can aged, sexed and raced with some confidence. It is important to use as many characters as possible, in combination.

Snow Buntings in The Wirral

The following, very instructive, illustrated photographs have been produced by Phil Woollen.

This 1st year male 'nivalis' bird was present on St Agnes Scilly on at least 2th October 2012.

extensive white inc white p. cov's = male
white, buff-fringed rump feathers = 'nivalis'

2 generations of tertials = 1st yr
(longest paler and more worn)

The pale, frosty mantle which appears to be characteristic of 'nivalis' may not be useful for all birds. Occasional records, such as a bird viewed at Fishguard Outer Breakwater during a ringing session (but not trapped, unfortunately), may throw some doubt on this feature. Something to assess over time.

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