Another source of information I am currently seeking is old Bird Observatory reports - pre 1977. Thus far I have only managed to source reports for Rathlin Island BO and Tory Island BO from the 60's and will get Copeland BO records in the next week or two. I have yet to get any feedback for Saltee BO, Cape Clear BO, Loop Head BO and Malin Head BO, so if you have any contacts, please let me know.
As the data, pre 1975, is limited, I will only focus only scarcities and rarities in that period. The current Irish ringing species list I have accrued stands at over 270 species but I expect this to rise a little further with the addition of a few more yanks.
The data of course is not perfect with overlooked late submissions, altered records, missing data, mistakes by previous editors and my own mistakes. This is unlikely to change for the foreseeable, until the BTO finally track back and digitise all the historic ringing data.... which might take a decade or two.
The data should therefore be taken at face value - it isn't perfect but is representative and fit for purpose.
I plan to filter the information out, post by post on the blog, covering a few species at a time. I will try and graph the 'All Ireland' totals from 1975, with North and South separate from 1977. At this stage I will focus on passerines, near passerines and birds of prey. I will also map the recoveries of these groups coming into and out of Northern Ireland (but no inter Irish movements). I have restricted myself to the North at the moment because the dataset is much smaller and my spare time isn't limitless!
The data will go in someway to present the population trends in some species but for some species it is flawed. Changes in techniques, improved equipment, the use of tape lures, the number of ringers & their effort, the closure of Bird Observatories, BTO periodic species targets (i.e. Swallow Roosts, Sedge Warblers in Ireland) and changes in birds behaviour (Finch species visiting feeders for example) etc. all have a huge affect, meaning it is not truly representative.
The BTO has national standardised programmes in place such as Constant Effort Site (CES) scheme and Retrapping Adults for Survival (RAS) scheme which are fantastic for assessing population dynamics, along with the Nest Record Scheme (NRS).
Goldfinch
As a ringer in my mid 20's and in the game for c4 years, I have always known Goldfinch to be a common bird and one that is caught in big numbers. But this wasn't always the case and many ringers still remember when it was a nice catch. The graph below really highlights the large increase in birds being caught, which is generally a reflection of the increase in the population. In 1982, only 6 Goldfinch were ringed in Ireland, compared to the best year of 1538 birds in 2013.
Over 10,000 have been ringed since 1975 and this figure should rapidly increase with todays yearly totals.
The controls/recoveries of Goldfinch into and out of Northern Ireland also show a similar trend in terms of dates. The majority of these mapped below have occurred after 2007.
With the exception of the one bird coming in from Scotland, the rest show a very similar migration route. The Calf of Man Bird Observatory is central to the route with 2 controls coming during spring migration. Copeland Bird Observatory is also key as a staging site for the birds heading south east, accounting for four birds in late autumn.
Those displayed are the only ones available to me at this time.
Goldfinch movements into (green) and out (red) of Northern Ireland
Greenfinch
The Greenfinch unfortunately is experiencing an opposite trend, with a large reduction in population. The finger can firmly be pointed to the disease Trichomonosis for the crash. Greenfinch were formerly one of the most common species ringed, which is represented in the map below. These days however, they are much reduced - in 1991 2474 were ringed In Ireland and only 313 in 2014.
Over 46,000 have been ringed since 1975.
The mapped recoveries below do not show any particular trend but do highlight that many more birds are recovered in Britain, with the much greater density of ringers. The dates and age stages of the recoveries are very interesting and in general show a similar theme of Greenfinches coming to winter in Ireland and returning to Britain to breed. They are also the opposite to Goldfinches in that the majority of these recoveries are from the 80's and early 90's, with only one in the 00's (2007/2008).
The Calf of Man BO is again focal, with three different birds being trapped there on migration.
Greenfinch movements into (green) and out (red) of Northern Ireland
I must also add a quick thank you to people who have assisted me in getting information - Dr Ken Perry, for access to his extensive ornithological library, Niall Tierney (the current editor of the Irish Ringing Report) and Niall T Keogh from Birdwatch Ireland, Neal Warnock (RSPB NI) for the Rathlin data and Peter Phillips for the Tory records.
NTK, Neal and Peter are all big patch birders and you can check out information for the former two at http://patchbirdingireland.blogspot.co.uk/ and the later on his Tory Island Bird Blog - http://toryislandbirdblog.blogspot.co.uk/
Check out http://dublinbaybirds.blogspot.co.uk/ for some of N Tierney's ringing exploits in the South.
I have not given permission for any of these pictures, graphs, diagrams or the data itself to be copied. If you are interested in something in particular, please get in touch.
Richard D
No comments:
Post a Comment