mid-August mixture (25 August 2005)
There is such a lot happening at this time of year, with many birds in moult. In their post-juvenile moult many birds emerge from a drab, unisex plumage into a more distinctive dress in which, in some species, the sexes are distinguishable. Typically, at the time that the bird has dropped its old (juvenile) greater coverts, the post-juvenile moult will have progressed sufficiently for it to be sexed. This effect is demonstrated first in a juvenile Bullfinch Pyrrhula pyrrhula ringed at Woolston on 15 August 2005:
Its heavy moult is indicated by the white flecks of feather scale, and some of the breast feathers are newly-grown and obviously the 'buffish grey-brown' (Svensson) colour of the female. For any readers wanting a reminder of the 'adult' plumage, the following image of a male and female was used previously on these pages:
Returning to the Woolston juvenile bird, the difference between the juvenile and post-juvenile feathers is also shown in this close-up photograph of the breast:
The link with the stage of greater covert moult is shown below. She is retaining 6 old greater coverts, an unusually large number for a Bullfinch in Britain, having recently dropped the innermost four juvenile gcs:
This Bullfinch had not yet started its head moult to acquire the black crown of an adult-type plumage. In Blackcaps Sylvia atricapilla the crown colour is, of course, the feature used for sexing and indeed the characteristic that gives the bird its English and scientific names.
The same general picture applies: when the new greater coverts are growing, the bird should be sexable. To illustrate this 'rule of thumb', my thumb appears in all of the following images! The following five Blackcaps, all ringed on the same day (15 August 2005) at Woolston, illustrate progressively, from top to bottom, five birds in various stages of post-juvenile moult from just beginning through to almost complete. In each case the greater coverts and crown are shown alongside each other for the same bird. These birds are retaining (from the top) 3, 1, 1, 2 and 1 old greater coverts, and are male, female, female, male and male.
It can be trickier to distinguish the two shades of brown in females than it is to see the black of males. It is usually easiest to see the emerging crown feathers by looking from the back of the head, as shown above, but it is difficult in the second bird from the top, and a side-on view, given below, more readily reveals the tufts of brown colour sprouting from the pins just above the bird's eye:
Finally, when the new greater coverts are fully grown, it is likely that the new head feathers will also have all appeared, as in the female shown below, also ringed on 15 August 2005. She has retained 1 old greater covert:
Even though her crown moult appeared to be complete, a few traces of body moult are betrayed by the flecks of white feather scale, and the still-emerging feathers underneath her eye:
Note the great range of stages of moult, amongst birds of the same species caught on the same day at the same site. The onset of post-juvenile moult is probably determined in part by the time elapsed after the bird fledged from the nest, and partly by its condition and general health.
As commented previously, Lesser Whitethroat Sylvia curruca has a south-easterly distribution in Britain and is the least-frequently encountered of the four Sylvia warblers breeding in north-west England. Members of Merseyside Ringing Group never tire of admiring these perky little birds:
The dark grey behind the eyes gives them a piratical look, and many individuals, including this one, have a pure white throat:
This bird (caught at Woolston, 15 August 2005) was readily aged as a first-year bird, Euring age code 3, partly from its dull iris, but the easiest ageing characteristic was its tail. It had accidentally lost the outermost five rectrices on the right side, the replaced adult-type feathers contrasting obviously with the juvenile feathers in the rest of the tail. The adult-type feathers have more white, especially on the tips of r2-r5, and the white on the outermost r6 is purer, again particularly near the tip. The body of the feather is obviously blacker on the renewed r2-r5. It is quite unusual to find a Lesser Whitethroat with as much white as this on r2-r4.
Reed Buntings Emeriza schoeniclus caught at Oxmoor Local Nature Reserve, Runcorn on 23 August 2005 allowed nice comparisons of the tail of an adult (left) and first-year bird (right), that of the adult being more rounded and with a tendency to have more extensive white on the outermost two pairs of rectrices:
It was easy to identify the adult bird as it was coming towards the end of its full moult, juveniles having only a partial moult - not involving the flight feathers - until their second calendar year of life. Many first-year birds, however, moult some or all of their tail feathers, and another useful ageing characteristic is the rounded primary coverts of adult birds:
Reed Bunting is another of the birds that acquires the breeding plumage on the head by abrasion, like Chaffinch Fringilla coelebs, Brambling Fringilla montifringilla and Yellowhammer Emberiza citrinella that have been depicted on these pages previously. As noted before, all are species that flock in winter, and camouflaging the head is probably an adaptation to reduce intra-specific aggression during the winter, whilst allowing birds to assume their breeding plumage without the energy expenditure of another moult.
By the next breeding season, he should be looking like this bird, photographed on 10 May 2005:
However, we should beware that there is considerable individual variation in this species, and unwary ringers can make mistakes. The following bird is an adult female, ringed at Oxmoor on 19 July 2004, definitively identified as a female by her active brood patch and small size (wing of 73.5mm):
Birds caught at night are not so easy to photograph, but some recent examples provide a couple of 'mystery photos', taken with flash:
Any ringer of waders (shorebirds) will probably have little difficulty in identifying the first image as the mantle of a Snipe Gallinago gallinago:
The second 'mystery' image depicts the coverts of a juvenile Dunlin Calidris alpina. In autumn, especially August, Dunlins of the schinzii race, bred in Iceland or Greenland, pass quickly through Britain, pausing only to fatten up to fuel their onward journey to winter in west Africa. On 8 August our small sample of 22 birds weighed from 35g to 60g, probably showing that the lightest birds had just arrived from the north, while the heaviest were ready to depart.
A surprise capture, in a mist-net catching roosting Swallows Hirundo rustica at Frodsham, was two Stonechats Saxicola torquata. This species has featured on these pages before, when a breeding pair was trapped on Walney Island in May 2004, but both of the Frodsham birds were juvenile birds just starting their post-juvenile moult and growing a new generation of greater coverts, although the crown feathers are still juvenile:
Especially at first glance in the dark, it is not trivial to identify the species, separating Stonechat from the congeneric Whinchat Saxicola rubetra, but the amount of white on the rectrices, and the wing length and wing formula, are diagnostic. Comparing the lengths of primary feathers, counting from the outside of the wing, Whinchats have the second primary falling between the 4th and 6th (p2 = p4/ p6), while Stonechats have p2 = p6/ p8. As it happens, this is almost identical to the difference between Chiffchaff Phylloscopus collybita and Willow Warbler Phylloscopus trochilus. The wing formula expresses the simple facts that shorter-distance migrants (Stonechat and Chiffchaff) have a shorter and more rounded wing, while the longer-distance migrants (Whinchat and Willow Warbler) have a longer and more pointed wing.
The effect is not perfectly shown in this photograph because the tip of the third outermost primary (p3) is tucked behind that of p4, but the rounded wing is still evident. For both birds, the tip of p2 fell between p6 and p7. For this wing formula, the primary feathers are counted from the outside of the wing inwards.