We have had 10 boxes up for about 10 years now. We have had Bluebirds every year. This year 9 of the 10 boxes were nested in. 8 of the 9 successfully hatched and raised, but all just one batch. What is odd to me is that none of the 8 breeders tried raising a second batch...and stranger still they all departed together either last Saturday or Sunday. Gone. All of them are gone. Why did they leave? Usually a least a couple of pairs tough out the winter - the others are generally gone by the first week in October...but they are all gone now. Any idea why?