Sunday, 2 August 2015

Oxwich Marsh: review of the year to date

July was a frustrating month.  We lost more days to wind and rain than we might expect in any month outside December to February inclusive, and this at a time when the marsh has been alive with juvenile birds.  

Notwithstanding this, if unique birds are considered, we are slightly ahead of where we were at this time last year.  The number of unique birds, by species, trapped between 1 January and 31 July inclusive in 2015 and 2014 respectively is shown in the table below.

Species 2015 2014 Difference
Jack Snipe 1 0 1
Snipe 2 0 2
Sparrowhawk 0 1 -1
Woodpigeon 0 1 -1
Kingfisher 1 2 -1
Green Woodpecker 1 0 1
Great Spotted Woodpecker 18 12 6
Swallow 1 1 0
Wren 41 34 7
Dunnock 35 38 -3
Robin 39 38 1
Stonechat 0 2 -2
Blackbird 22 12 10
Song thrush 10 0 10
Mistle thrush 1 0 1
Cetti's Warbler 14 10 4
Grasshopper Warbler 2 2 0
Sedge Warbler 38 33 5
Reed Warbler 44 56 -12
Lesser Whitethroat 1 1 0
Whitethroat 11 12 -1
Garden Warbler 1 1 0
Blackcap 59 111 -52
Wood Warbler 0 1 -1
Chiffchaff 30 19 11
Willow Warbler 23 28 -5
Goldcrest 6 3 3
Long-tailed Tit 12 1 11
Marsh Tit 0 1 -1
Coal Tit 0 3 -3
Blue Tit 207 202 5
Great Tit 111 102 9
Nuthatch 1 0 1
Treecreeper 3 1 2
Magpie 1 1 0
Chaffinch 162 101 61
Greenfinch 202 235 -33
Goldfinch 320 224 96
Siskin 49 62 -13
Lesser Redpoll 3 0 3
Bullfinch 11 6 5
Reed Bunting 60 100 -40
Total  1543 1457 86

So far in 2015 the highlights in species terms have been the new birds for the site (since ringing recommenced in February 2013): green woodpecker, nuthatch, mistle thrush and lesser redpoll, and the continued good variety of species captured.  We have not had a completely unexpected bird (such as the wood warbler in May 2014), but the numbers have been good in spite of the weather.  August and September are the most exciting months of the year in terms of birds passing through the marsh.

It should be noted that there is very limited scientific validity in a direct comparison between the two years, and the difference between years is included for interest only.  There are various reasons why a direct comparison is not possible, including:
  • In 2015 we have been more active, and have made more visits to the site.  
  • We have also put up more net than in 2014, and tried out some new net rides.  
  • In 2014 we did more ground baiting, but discontinued this in 2015 when pheasants began exploiting the supplementary food source.  
All of these elements, and others, have contributed to differences between years.  However, there are some interesting changes and consistencies that are worth drawing attention to.  For example:
  • In 2014 we caught our first garden warbler on 26 July, while in 2015 we trapped our first on 31 July.  Exactly the same capture dates in the respective years applies to lesser whitethroat;
  • The pattern of reed buntings captures in June and July of the respective years has been very different.  We caught a lot of reed buntings in June 2014 and very few in July.  In 2015 this pattern has been reversed, possibly indicating later breeding.  Currently juvenile reed buntings are very obvious around the marsh.  The lower annual total this tear reflects the lack of ground baiting in 2015.  This reduced the numbers caught in late winter in particular.
  • The numbers of locally resident birds such as blue tit, great tit, dunnock, robin and wren are remarkably consistent, possibly reflecting the fact that a large proportion of the local populations of these species are trapped;
  • Blackcap numbers are well down.  This may reflect the problems getting sessions in in July, and it is notable that we are also down on willow warbler.  There is an influx of both species to the marsh in July, possibly as locally breeding birds disperse;
  • Finch numbers are both up and down depending which species you look at.  There is less evidence of disease in greenfinches this year (we have not had to stop feeding - which we did for a period in 2014 due to evidence of trichomoniasis), but the prevalence of the disease in 2014 may have had a lasting effect on the population in the area, which in turn has affected the catch in 2015.
  • Goldfinches have been consistently present and numbers in 2015 are substantially higher than 2014. Conversely we caught less siskins in the spring this year but they have persisted into July (they had left by early June 2014 whereas in 2015 there are signs that birds have had second broods) and the 2015 total has gradually crept towards that of 2014. 
The final July session (158 birds) made up for disappointments earlier in the month, with the catch including our first kingfisher of the year, two Cetti's warblers (juveniles), 7 sedge warbler, 14 reed warbler, a lesser whitethroat, 4 common whitethroat, a garden warbler, 13 willow warbler, 9 blackcap, 29 greenfinches and 2 lesser redpoll.  The redpolls showed a brood patch and cloacal protrusion respectively.

Thanks to all who have come along to sessions this month.

Photos, taken by Keith Vaughton, are below.

Owain Gabb
02/08/2015

Juvenile kingfisher.

Lesser whitethroat

Lesser whitethroat

Lesser redpolls

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