Bats Upside Down
Name: Drew H
When bats sleep upside down does all their blood rush to
their heads like when people are hanging upside down?
Bats are so small that, unlike humans, the problem of blood distribution is
not a huge problem. They are able to wrap themselves into a small package and
like most mammals, they can regulate blood flow by contracting their blood
vessels to direct and achieve blood flow.
Up-dated July 2008
I concur with the other answer here. I had noticed several sources on the internet
that describe "special valves" that keep blood from pooling in the head (I was
studying to co-lead a presentation on bats), however none of my bat books describe
this. In fact, the book "Flying Foxes" by Leslie Hall (2001) states: "It was once
thought that bats had a series of valves in their blood vessels which prevented
blood rushing to their heads when they were upside down. No such valves have been
found and it is considered that bat's small size and the small amount of blood allow
them to sleep upside-down." I would consider the valves a myth until shown otherwise.
The internet claims usually mention that similar valves in human veins prevent blood
from pooling up in our legs, however this mechanism relies on fairly regular movement
to "squish" the blood past the valves (which explains the discomfort of standing
motionless for a few minutes), and they are not important during the relative
motionlessness of sleep, since we sleep laying down. So in summary, the relatively
small size of bats (and many similar sized animals in the insect world that can rest
upside down) is probably the prime reason.
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Update: June 2012