[EBB Sightings] Re: mysterious death of w. bluebird and swallow chicks

Dear group,

I am asking this question for a friend of mine who is not on this email list. She has several acres of wild property out in
Morga, bordering on East Bay Regional Park lands (in Bollinger Canyon). For the past several years, she has had western
bluebirds and various species of swallows (including violet greens), as well as house wrens using bird boxes on her property. A
week ago, she went to check the bluebird and swallow boxes closest to her home, and found all of the fledglings in both boxes
dead. (The parents are fine.) The chicks were almost fully feathered and ready to fledge. She cannot figure out what happened to
them; there were no signs of assault on any of their bodies, either. She's wondering now if it could have been something in the
boxes (she got them from a reliable volunteer for the western bluebird project). Does anyone have any other theories? I know
wrens will sometimes destroy other birds' eggs, but I didn't think they would attack fledglings (and she saw no peck marks or
anything on the bodies).

Thanks for any help/ideas on this mystery...

Lisa