Below is a copy my recent correspondence with Alan Ball, which explains why there have been so few sightings of Barn Owls this year:
This year 2013 was the worst Barn Owl breeding year since 1950 (before my time) and we know that many adults did not survive the cold weather at the end of the winter particularly in March. The good news is that Lincolnshire probably fared better than anywhere else in the country and we were only down by 50% and we had a good end to the breeding season so hopefully will be back to reasonable numbers next year. My colleagues in other parts of the UK were down by 90%.
The triangle box on the tree this year was used by Grey Squirrels. They were also in the pump box – either going in after the Jackdaws had finished or taking the box from the Jackdaws.
Hopefully we'll be OK again in 2014.