17/01 Are 1st Winter Blue Tits scarce this winter.

We (I) have mentioned recently several time that there are fewer 1st winter birds visiting our feeders. I thought I would have a look at our data over the last 10 years for the Nov-Dec period for Blue Tit to see what it shows.

We operate three feeders at Bagnor (est 1985), Greenham (est 2010) and Snelsmore (est 2007). The charts below cover the last 10 years from the winter 2007/08 (Greenham 7 years). The data relates to structured ringing and is from two visit, one in each half of each month. (we often ring weekly but the additional visits are not counted). “Standard” nets are up by 08:00hrs until 11:00hrs. What we are looking at is abundance as the captures include individuals captured more than once. Flocks move around; individuals captured are often not recaptured again until around the same time the following winter.

Each of the charts shows a steep decline for 2016/17 with the 1st winter birds dropping towards 2nd winter and older birds. What is more interesting is that it has happened before and hasn’t been noticed in my perception. The winter of 2012/13 for instance shows the two ages converging except at Bagnor where numbers are towards the lower level of the others and recovering from a similar level the previous winter. Looking back through the 32 year history of the Bagnor Feeder, similar convergence has occurred before in the winters of: 2005/06, 2001/02, 1993/94, 1992/93, 1987/88. For some winters a drop in numbers of both ages is apparent and probably indicates a general survival issue whereas convergence of ages with adult (parents) levels maintaining would indicate a nestling or post fledging failure.  

Great Tit show similar but in lower numbers

Very basic stuff, I am sure it is more complicated than this but it stops me getting bored.

JanLegg