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

That is really odd. House Wrens will generally build a nest right on
top of an expropriated nest box, as will House Sparrows. The Wrens will
cover the old nest with coarse sticks; House Sparrow build big bulky
affairs often with string and other flotsam.

I wonder about Blowfly larvae. There are several species of Blowfly
which specialize in bird nests. The maggots draw blood from the toes of
the nestlings. Typically there aren't enough of them to cause death,
but if there's a huge population in the box, this might happen. The
maggots pupate and form firm 'cacoons'. Not silky cacoons like a moth,
but firm leathery looking ones. The larvae pupate on the floor of the
nestbox, underneath the nest. So you'd have to clean out the box to
find them.

     Rusty Scalf



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