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Re: COMPETING BATS, BIRDS & PTEROSAURS



Henri said:

"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, if one has good eyes."

I don't agree with either sentence. Taking the latter statement, bird visual
acuity is good, but echolocation (in bats and dolphins) is at least its
equal in many respects (ie. in terms of information the bat receives about
its prey, to enable it to capture that prey). The organs involved are also
adaptable to other tasks: pressure for more sensitive ears, which can also
be used to listen for prey movements; adaptability of echolocation signals
for different environments (open spaces, cluttered forest, etc); the ability
of pressure waves to "detect" things that vision cannot (eg. dolphins
detecting food under sand) amplification of acoustic signals to stun prey
(in dolphins).

However, that's moot in the context of what you're saying. If that was the
whole story there's no reason why bats couldn't share the air with birds, so
there must be other factors - the main one probably being why bats not able
to gain a foothold in bird-dominated airspace. If we assume that birds
appeared before bats, which seems reasonable even though the bat fossil
record is appallling, that means you have a gliding mammal - using a skin
membrane stretched across its forelimbs - trying to enter a niche occupied
by highly volant, feathered predators. I don't think it was going to happen,
but there was sufficient pressure to occupy a nocturnal niche specialising
on insects which are highly abundant in the few hours following sunset. This
would likely have driven the evolution of sophisticated echolocation, so I
don't think you can really use echolocation and vision to address the reason
why birds and bats don't occupy the same niche today.

Adam