Oxwich Marsh 6 September 2014

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A dull, overcast, windless but warm start to the day provided ideal conditions for catching birds. Unfortunately no-one told the birds to be in the marsh, and the overall result was similar to recent sessions in terms of numbers, albeit with local breeding species featuring more prominently than in recent weeks.
The catch was made up as follows:

Species New Re-trapped Total
Great Spotted
0 1 1
Wren 1 1 2
Dunnock 3 4 7
Robin 6 1 7
Song Thrush 1 0 1
Reed Warbler 4 0 4
Whitethroat 1 0 1
Garden Warbler 2 0 2
Blackcap 20 2 22
Chiffchaff 7 1 8
Willow Warbler 6 0 6
Marsh Tit 0 1 1
Blue Tit 9 11 20
Great Tit 2 0 2
Chaffinch 1 0 1
Greenfinch 2 2 4
Goldfinch 5 1 6
Reed Bunting 2 0 2
Total: 72 25 97

The features of the session were another good haul of blackcaps, two garden warblers, and a minor influx of Phylloscopus warblers, with chiffchaff slightly outnumbering willow warbler.  Only the second young song thrush of the year was trapped: this is one of the few species that we had caught more of at this stage in 2013.  There was no overhead passage of pipits noted, but a few grey wagtails were moving.
Pictures of willow warbler and chiffchaff are below:
Juvenile willow warbler

Juvenile chiffchaff
In the pictures above, the differences in head markings between juvenile chiffchaff and willow warbler are fairly clear – the obvious supercilium of willow warbler standing out.  In the hand the limit to the emargination of the primaries is always checked to confirm species (chiffchaff is emarginated to the 6th primary and willow warbler to the 5th).  However with a bit of practice over 95% of birds can be confidently speciated prior to this confirmation.  Ageing both species at this time of year is far more challenging, and may be the subject of a different blog post. 
Robins have appeared in number in the marsh over the past couple of weeks, and many of this year’s young birds have now completed their post juvenile moult, making them inseparable from adults in the field.  By way of contrast, reed warbler numbers were very low this morning, with the recent settled weather probably providing birds with a window to migrate.  We failed to capture (or record) a single sedge warbler.  It is nice to see the return of flocks of goldfinches to the feeding station, following a couple of months of low numbers.
The table below provides a monthly breakdown of the numbers of birds caught in the marsh in 2014, and also an indication of the diversity of the passerine community on a monthly basis:
Month: January February March April May June July August September TOTAL
Grand Total: 107 103 378 348 186 418 432 682 472 3126
Total Species: 10 9 16 20 24 24 24 31 28 41
Effort has varied between months, and direct comparison is not possible.  Early in the year many sessions were cancelled or foreshortened due to wind and rain.  In March and April large numbers of finches (particularly greenfinch and goldfinch) increased the catches markedly.  Many birds were on territory in May and not moving around to any great degree, and finch numbers dropped off by mid-month reducing the monthly total.  Spring passage catches of warblers were relatively limited. 
By June many locally breeding birds had fledged young, and catches increased as a result of the number of juvenile tits, finches, robins, dunnocks and other common species using the feeders and moving through the marsh.  We captured 53 new blackcaps in June, but only 3 sedge warblers and 8 reed warblers, indicating that breeding numbers were low.  Dispersal and migration of passerines was noted from July, and has continued to date.  The best month for species diversity and total birds captured was August (682 birds of 31 species caught).  However, in addition to the variety of birds moving through the area, this also reflects increased efforts including evening visits to target roosting swallows and mid-week sampling to attempt to ensure catches coincide with influxes of passage warblers.
A good if unspectacular session this morning.  Nice to see a goshawk over the reedbed, although the sentiment was probably not shared by the woodpigeon it was pursuing!
Thanks to Cedwyn Davies and Heather Coats for assistance and company.
Owain Gabb
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