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BATS, BIRDS, ECHOLOCATION & SIGHT
On mechanisms of competitive exclusion in birds, bats and pterosaurs,
Henri Rönkkö wrote...
>I believe birds do better than bats in daylight because
> birds rely on vision whereas bats rely on echolocation.
> Echolocation is neither as acute nor as effective as seeing,
Later on in the thread, Ron wrote...
> Let's not forget that not all bats echolocate, and some birds do.
Furthermore, let's not forget that many bats are far from deficient in
terms of eyesight. Some bats, notably megadermatids, have large eyes,
acute vision and hunt predominantly by sight, even gleaning *without*
echolocating (as Ron notes). They catch large arthropods, small
mammals and sleeping birds in this way. I need not say that megabats
have large primate-like eyes and visual centres in the brain.
Furthermore, as noted before, some microbats hunt in the day on
islands devoid of predatory birds.
As usual therefore, there are few black and white rules, but lots of
shades of grey. Bats may do better at night because of
thermoregulatory constraints, and they may actively avoid competition
from birds, but this doesn't necessarily restrict them to nocturnal
behaviour - there does not seem to be one simple rule that dictates a
dichotomy in bird and bat behaviour. Perhaps the constraints of
ancestry provide another answer: branch-leaping proto-bats (sensu
Fenton) were probably nocturnal, and most descendants of these
ancestors simply stayed this way. There are excellent text-books by
Fenton, Altringham and Hill and Smith that discuss these areas in
much greater depth.
To bring this round to pterosaurs: the (largely) naked patagia of bats
apparently restrict their foraging period. Pterosaurs had naked patagia,
but I find it very hard to think that they were nocturnal (diurnality is
implied by their many visual display structures). Were pterosaurs better
at temperature regulation than bats, perhaps because of their
pneumaticity? Or is it bats which are strange in being mostly nocturnal,
and in adopting a uniquely mammalian approach to the problems of
being a flighted tetrapod?
Ron - is the turtle book out yet?
"Craig's in the bedroom, asleep like a kitten - this man could sleep, for
the whole of Great Britain" - - Caroline, 2000
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