Deserted nestlings

[Boilerrph1996]

I live in mid-northern Indiana and it seemed like a weird Martin year here. The PMs arrived probably 3-4 weeks later than normal, and seemed to leave earlier, probably mid August. I put a new a new quad pod pole and 8 compartments up this spring, to go along with the 1 I already had. Probably my 5th year having PM. The new home was nested a bit later than the original, and the nestlings were a few weeks behind the original house when I checked in July. Noticed there was no activity around mid August, and finally lowered both houses to clean mid Sept. The original pole was fine, but the new pole had 3 nests in which the nestlings were deceased. I'm only speculating, but it appears they were deserted because they weren't big enough to fledge. I haven't had this happen before. Does this occur on occasion?

[Bird Brain]

My guess would be heat related morbidity for the second pole. You said they nested late. If units aren't ventilated thoroughly, late nesters have little chance to survive the heat, even in Indiana. Consider adding more ventilation to all your units.