Sunday, 16 August 2015

Oxwich Marsh 15 August 2015: an autumn redstart

A predominantly bright day, with a gradually strengthening westerly wind.  In addition to 560 feet of standard nets in a mixture of scrub, reed bed and ruderal (with scattered scrub) habitats, we also put a series of two-shelf nets along an earth bund through an area of dry reedbed with stands of bracken and scattered rosebay willowherb.  The latter proved very successful, as the bund separated two areas of similar habitat, and birds regularly moved across it: it was also relatively exposed, and the birds were moving below the height of the marginal vegetation.

The catch was as follows:

Species New Re-trapped Total
Great Spotted Woodpecker 0 3 3
Wren 3 0 3
Dunnock 1 2 3
Robin 1 3 4
Redstart 1 0 1
Blackbird 0 2 2
Cetti's Warbler 0 3 3
Grasshopper Warbler 2 0 2
Sedge Warbler 12 1 13
Reed Warbler 8 1 9
Whitethroat 5 0 5
Blackcap 1 1 2
Willow Warbler 6 0 6
Blue Tit 13 8 21
Great Tit 1 5 6
Chaffinch 1 2 3
Greenfinch 23 3 26
Siskin 0 1 1
Reed Bunting 0 1 1
Total: 78 36 114

The features of the catch were:
  • A female common redstart, the first of this species to be captured at the marsh since ringing recommenced in February 2013;
  • The sixth and seventh grasshopper warblers of the year, both of which were young birds undergoing post juvenile moult;
  • A good day for whitethroats, with five young birds captured;
  • A steady catch of reed and sedge warblers.  We are awaiting a real fall of both species - and are behind the game with regard to sedge warbler in comparison with 2014;
  • The continued good catches of greenfinches.  All were juveniles, with some not having started their post juvenile moult.  All appeared healthy, with no evidence of trichomonosis at present, which is good news.
  • The lack of blackcaps.  A week ago 240 feet of net returned 23 blackcaps.  This week, more than twice the amount of net returned only two birds.  
Ageing of female common redstarts is difficult, as adults undergo a complete summer moult and young birds a partial post juvenile moult.  It follows that both adults and juveniles of both sexes have fresh plumage in the autumn (albeit juveniles may show a little more wear to the primaries and tail feathers and a moult limit in the greater coverts).  In males, clear moult limits in the greater coverts in 1st winter birds, the extent and purity of the white tipping on the throat feathers and of the white band above the eyes can all be used to determine age,

Photographs are below.

A first winter lesser whitethroat from earlier in the week.  Aged on the basis of the uniform olive colour of the iris and the pattern of the 5th tail feather (Owain Gabb)

A female redstart.  Tentatively aged as a first winter. (Keith Vaughton)

Female common redstart (Keith Vaughton)

Great spotted woodpecker.  The darker red coming through on the hind crown indicates this is a male (the juvenile red feathering on the rest of the crown is being moulted out).


Thanks to Val Wilson, Heather Coats, Wayne Morris, Cedwyn Davies and Keith Vaughton for company and assistance on Saturday.

Particular thanks to Val for scribing and to Cedwyn for taking the initiative to set the two-shelf nets. The redstart, grasshopper warblers and all but one of the whitethroats came from them.

More information on trichomonosis can be found here:
http://www.bto.org/volunteer-surveys/gbw/gardens-wildlife/garden-birds/disease/trichomonosis

Owain Gabb
15/08/2015

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