Oxwich Marsh 4 Sept: 2000 new birds in 2014.

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A very bright and warm day.  The wind picked up mid-morning, but had died off by the afternoon.  As a result we were able to do both an early session in the scrub, reed bed and fen meadow, and to try for a swallow roost in the evening.  The results were excellent.  Numbers by species are in the table below:

Species New Re-trapped Total
Sparrowhawk 0 1 1
Great Spotted
0 1 1
Sand Martin 10 0 10
Swallow 178 0 178
Tree Pipit 3 0 3
Meadow Pipit 2 0 2
Wren 3 0 3
Dunnock 0 2 2
Robin 6 1 7
Blackbird 0 1 1
1 2 3
1 0 1
Sedge Warbler 2 0 2
Reed Warbler 3 1 4
Whitethroat 0 1 1
Garden Warbler 1 0 1
Blackcap 21 1 22
Chiffchaff 2 0 2
Blue Tit 12 9 21
Chaffinch 0 1 1
Greenfinch 5 0 5
Goldfinch 6 0 6
Bullfinch 2 3 5
Reed Bunting 1 1 2
Total: 259 25 284

The features of the morning catch were a re-trapped sparrowhawk, three more tree pipit and our first two meadow pipit of the autumn, a new Cetti’s warbler, our fifth grasshopper warbler of the year, another good haul of blackcaps and a garden warbler.
Our fifteenth new Cetti’s warbler of the year.  Including retraps, we have captured 19 unique birds on the marsh in 2014.
The sparrowhawk, a young male, had lost slightly in excess of 5 grams in weight since it was initially captured in August.  Nothing a blue tit can’t sort out (typical weight around 10 grams!). 
It was nice to catch both tree pipit and meadow pipit, albeit the birds were caught at different times in the session so a photograph illustrating differences was not possible.  The differences in flank streaking (tree pipit has weaker more diffuse streaks), belly colour (tree pipit is whiter), and head pattern (tree pipit has stronger markings) were all obvious in the hand.  However it was also interesting to note differences in hind claw length (the three tree pipits showed hind claws of 6.8mm-8mm and the meadow pipits 13mm and 14mm respectively) and bill depth (tree pipits have a sturdier bill and measured 4mm-4.6mm with the meadow pipits measuring 3.5mm and 3.7mm).  Bill depth is measured between the nasal cavity and the head using callipers.
Meadow pipit.  Note the long, narrow bill and lack of strong head pattern in comparison with the tree pipits photographed for previous blog posts

Meadow pipit.  Note the long hind claws.
The grasshopper warbler was a juvenile.  It was not carrying significant fat.  However many of the blackcaps and the garden warbler were, indicating that they were moving actively migrating.  Numbers of reed bed warblers remained low.
Grasshopper warbler.  The fifth of the year.
Blackcap.  We have now captured 218 new blackcaps on the marsh in 2014.

Garden warbler.  The 19th of 2014.  A scarce autumn passage bird in Gower
The evening session was a success.  The only disappointment was that house martins, which had been present in good numbers in the early evening, did not come in with the swallow flock.  Small numbers of sand martin were trapped.
In the hand adult swallows can be sexed on the basis of total tail length (male 93-132mm, female 76-112mm) and the distance between the longest and shortest tail feathers or ‘tail fork’ (male in excess of 51mm, female 35-58).  There is some overlap in both of these measurements, and some tails showed broken ‘streamers’, but the majority of adult birds could be determined to sex.  Juvenile sand martins show pale fringing to their tertials and coverts and have very little wear to the tips and edges of wing feathers.  Adult birds have more uniform wing feather colouration.
Other visitors to the nets were a wren and a brown long-eared bat.  The bat was easily extracted and released.  A noctule had been seen at dusk flying powerfully over the reed bed prior to the swallows coming in to roost.
An excellent day.  Thanks to Cedwyn Davies and Keith Vaughton, who were able to come in both the morning and the evening, and to Cedwyn for acting as scribe for the roost session.  Also good to see Wayne Morris for the swallow roost.

Owain Gabb

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