To check or not to check?

Boxes that is.
 With the cold weather holding everything up this year I was beginning to wonder if nesting would ever start, but encouraged by seeing a Blue Tit in my garden taking nesting material somewhere (obviously not to one of my boxes) I thought it may be time to check some of the small boxes on our sites.
Starting with our Tree Sparrow colony, from 22 boxes there were 4 with 3/4 built nests and 5 with complete nests although not lined with feathers yet, good start, the rest were empty apart from 2 that contained half built nests of moss, so they belonged to either Great or Blue tits. Based on these findings I think I will leave checking our woodland site for another week.
 This recent run of good weather has obviously encouraged the birds to start nesting.
This time last year some of our Tree Sparrows had already hatched, so it looks like we're behind by about 3 weeks.