Baker, I can think of two possibilities. One is that they have not started incubating yet. Bluebirds can lay up to 7 eggs. Once the eggs are in the nest, the incubation does not need to start right away. Also, the mother may leave the eggs for longer periods if it is hot out. Another possibility is that you have a wasp nest in the box. They will abandon nests where wasps have set up shop. Check on the roof for a wasp nest. To avoid this, always rub paraffin wax or soap on the roof of the house. Or you can rub a thin coat of vaseline on the roof and about 1/2 inch down on the sides. You should be sure to wipe this out well with a paper towel leaving a very thin coating. Ideally this should be done in the early spring before the nesting season, but you could still do it now.

They can but once the female starts incubating you don't see them very often. You may just be missing them. What you could do is very carefully take a sharpie and mark a small dot on one of the eggs and then check the next day to see if the mark has moved. The eggs are turned during incubation so the dot should not stay in the same place. Even if the dot doesn't move though give the eggs the proper 14+ days to hatch, so count from the day the last egg was laid and then at least 14 days from that date to decide if the eggs aren't viable anymore. I have had a male go missing when the female was incubating, he was gone for four days but she as still there. Good luck, hope you are just missing seeing them.

i was reading this thread with interest. i have a situation where it appears i have 8 bluebirds who have hatched in one nest (thursday may 2, they were born). it may be 9, it's hard to tell. while monitoring the nest in late april i noticed what appeared to be eggs missing from the 3 that had been laid earlier in that week. the reality was that the eggs had been pushed down deeper into the nest and covered with pine straw. the mother kept coming back (may have been another species coming in and covering the egg with straw? i have seen no house sparrows here at all) and eventually she started laying again. turns out, there were 10 eggs total in this nest when she was done! i guess five from the first attempt and 5 after that. bottom line, 8 babies are in there now. i'm putting out meal worms twice a day and making sure there's lots of water nearby in the bird bath, and plenty of shelled sunflower seeds for the parents nearby in that feeder. anyone ever seen or heard of a situation like this?

Well If you have ever seen TRES fledge theres no way a baby Blue will make it. I would almost opt to candle the eggs and if there is little to nothing there get rid of them. Is it possable to tell the difference between babies at hatching time? I would want to put them in the Blues nest but that could cause problems too. Lets think babies not eggs here. No way a blue can survive with a TRES Mom, overloading a Blue or having babies hatch days before her clutch could result in dead babies. Yikes this is one for Bet, Malinda or Cornell. Im still thinkin destroy the eggs so no babies ever suffer.