I have mentioned in some of my previous posts that the ringing totals at Titchfield Haven have been considerably lower this year than last year, and that the percentage of adults birds ringed has been much higher this year, than last. So given that more typical British summer weather had once again returned, and there was no chance of ringing on Saturday I thought it would be an ideal time to do a bit of analysis. Initially I was just going to compare 2011 totals with 2012, but seeing as last year was such a fantastic year for several species, and was not typical for the site, I thought I would also include 2010 in my totals.
Bird ringing at Titchfield Haven has been carried out since the early 1970's, but it was in 1999 that we started ringing at the current location. We adopted a standardised approach, whereby we only ring on three days in any week, and we use the same number of nets during each session. This has meant a high level of commitment from the ringing team, but it does allow us to make some useful comparisions from year to year.
For this analysis I have chosen a selection of species, the dates chosen are from our first sesson of the year through until the 23rd August. The totals for each year are summarised in the graph and table below.
From the graph it is possible to see Sedge Warbler is the to most numerous species ringed at the site, and last year over a thousand birds were ringed up to 23rd August, and the second most numerous species switching between Grasshopper Warbler and Reed Warbler. The surprise last year was the amazing numbers of Grasshopper Wablers ringed, with 564 captured. Other species that seemed to have a good year were Common Whitethroat, Blackcap and Garden Warbler, with 97, 61 and 76, ringed respectively.
Looking back to the 2010 totals it is possible to see just what an amazing year 2011 was, and a real blip, which presumably was down to the weather conditions, which were ideal for migrant birds to breed. This year, as we all know, the weather has at times been atrocoius, and after an early warm period in April, May and June turned out to be a wash out. Unfortunately, these conditions were not ideal for summer migrant species, but our resident birds were able to take advantage of the warm April weather. The totals for 2012 seem to reflect this, with Sedge, Reed, Grasshopper and Garden Warbler and Common Whitethroat all significantly down. The Blackcap is down on last year but up on the 2010 total, whereas as Blacbird, Robin and Wren are all on a par with 2011, or have done better. The worrying trend is the steady decline in the numbers of Willow Warblers ringed, even in 2011.
So the next thing I have done is looked at the percentage of adult birds within the ringing totals. The reason I have done this is because during our ringing sessions this year we felt that we were catching a higher than normal percentage of adult birds for the time of year. The significance of this could be that some summer migrant species have had such a bad breeding season, that the adults have given up trying to breed and started their autumn migration.
From the analysis it is interesting to see that in fact our feelings were correct for some species, but not for others, but the most noticeable species was Garden Warbler, where over 55% of the birds captured were adults. Other species with a higher percentage of adults were Reed Warbler, with 44%, Blackcap, with 23%, Common Whitethroat, with 9% and Willow Warbler with 9.5%. The higher parcentage of adult Cetti's Warbler, Blackbird, Robin and Wren are probably due to an increase in the number of breeding birds in the ringing area.
|Species||% of Adult Birds Captured|
So what does all this mean? Well obviously this study only relates to our ringing totals at Titchfield Haven, and up to the third week of August. But the results seem to suggest that some summer migrant species have had a poor breeding season, as the number of juvenile birds passing through is down on both 2011 and 2010. Whereas some resident species, such as Blackbird, Robin and Wren, and some migrant species, such as Chiffchaff and Blackcap seem to have had a good breeding season. Willow Warbler appears to be on a steady decline. The number of adult Grasshopper and Sedge Warblers captured is lower than the two previous years, which could suggest that birds are breeding later, certainly at the time of writing this we were still catching Reed Warblers that appeared to be feeding young. I guess we will just have to see what the second half of the season brings, I will keep you posted.