One of my reasons for finding ringing so interesting is that you can put some tangible figures on the population levels and productivity of some of our commonest birds.
Many garden bird enthusiasts have commented to me that there seems fewer Blue Tits in their gardens this winter. Do our ringing returns support this view?
A trawl through our database came up with the following figures for our ringing of Blue Tits at Leighton Moss.
2006 480
2007 338
2008 242
So yes 2008 has been a very poor year. Perhaps even more telling is the proportion of adult birds in the catch. Adult and first year Blue Tits can easily and reliably be told apart in the hand because the young birds retain the greenish juvenile feathers on the primary coverts.
In 2006 only 7 % of the birds we caught were adults, a sure sign that productivity was high. In 2007 this increased to 21% and this year to 25%. So the last two years have seen low productivity mainly due to the unusually wet weather either during or just after the nesting season, making invertebrate food hard to find and so causing high mortality among the young inexperienced birds. The Leighton birds were caught in the scrub and reed bed areas and were not taking artificial food.
A catch today of 35 Blue Tits at a feeding station in Arkholme produced an amazing 55% of adult birds. The high numbers may partly be explained by adults relying on their knowledge of a good feeding station and so returning in succesive years whereas young birds have to discover the good sites for the first time. It was also noticeable in this admittidly small sample that adult birds were on average a gram heavier that young birds.
One side line to this is that Coal Tit numbers have been the highest on record with lots of young birds. Coal tits nest mainly in conifer areas and also nest somewhat earlier than blue tits so may have escaped the worst of the bad weather.
John Wilson
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