I have been doing the BGBW for a number of years and in common with many other posters feel that te birds are playing hide and seek with me! This year, we went from pub grub to gastropub food. We put out nyjer seeds, got someone to shell the sunflower seeds so that there were just hearts, bought some grated cheese from the supermarket and even put out some mealworms! I had had the notices up for days about the free food and we were way out in front of the neighbours!
Yes, the results were better (particularly starlings) but both the wrens were noticeable by their absence as were the pair of bullfinches (a page 2 bird). The normal group of 6 chaffinches was represented by a single member!
So, my question to the PTB (Powers That Be) is, in the absence of any way of acknowledging absent friends, how is the result representative of our bird population?
They rely on the very large numbers taking part.
Some people will miss things they normally see, others will see birds that only occasionally come into their garden. Some people will put out more food, others less, others different types. Some people will have a cat sitting there scaring all the birds away.
On average though, these things are pretty much the same from year to year. This means that when they crunch the numbers they can spot trends with high accuracy. It is the trends that are important, not the actual numbers of birds seen.
I think that there are also a small number of people who act as reference watchers, they perform regular counts throughout the year. This would help gauge the numbers of birds that would normally come into gardens but are missed. It also allows them to take account of the weather.