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I wanted to report on an event that occurred during the cold wet weather we
had this past weekend, because I learned something about tree swallows as a
result that may be useful for anyone who managers or monitors tree swallow
nest boxes.

I went around to check our nest boxes yesterday evening, all of which were
last checked on June 16 and at that time contained thriving families of
nestlings at various stages of development. Yesterday's check found dead
tree swallow nestlings in four different boxes -- a total of nearly 20 young
birds.

The sole bluebird family was spared, along with three sets of swallow
nestlings. There was no evidence of any sort of attack, so I was baffled.  I
wrote to the Cornell bluebird list for help, and many experienced people
suggested that it was almost certainly the cold rainy weather that was to
blame.  It seems that because tree swallows are exclusively insectivores and
catch food exclusively on the wing, they suffer when the weather turns cold
and wet.  The rain suppresses the flying insects, the swallows must range
farther from the nest to find food, and they either can't find enough, or
the young become hypothermic because the parents are spending so much time
away.  Bluebirds, on the other hand, will catch bugs on the ground when it's
rainy.

This was interesting and new behavioral information for me so I thought I'd
share it -- even though it may not be news to some folks here.  I had no
idea these birds were so vulnerable to the elements.

I also made an interesting related discovery that is slightly off-topic, but
since we sometimes discuss entomology here, I thought I'd share this as
well.  When I went around cleaning the dead nestlings and nest material out
of the boxes this morning, every box contained two giant carrion beetles,
also known as American Carrying Beetle (the birds had been dead a couple of
days).  It's a gorgeous beetle.
http://www.dnr.state.wi.us/org/land/er/invertebrates/beetles/amerburying.htm
Apparently the males find carrion during the night, then emit pheremones
that attact females.  That explains why I found two in each box.

The reason I mention this is that I discovered while researching it this
morning that this beetle is listed federally as a critically endangered
species.  It's in significant decline around the nation... it used to exist
in 35 states, but now is found only in 4... for example, the last one was
seen in Wisconsin in 1953 -- yet I saw not just one, but 8 of them in the
space of half an hour.  This struck me as interesting enough to be worth
reporting on.  There is no question whatsoever that this is the beetle I saw
-- it is very distinctive.

Miriam Lawrence
Monkton, VT