Birds would be expected to have greater species richness than terrestrial animals.
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This is due to the ability of birds to more easily move from island to island. We do indeed see great species richness for birds in island environments and less for snakes and lizards. In fact, many islands that are great exemplars of bird diversity have few lizards and few or no snakes whatsoever. There may be a compound effect here in that there is very little predation of birds on these islands by native species, so the inability of animals such as snakes to immigrate to an island also allows the birds there to thrive in many more niches than would be possible with the introduction of this predation.