Beavers is one of two buildings in Institute Road to have a plastic owl, and there are at least two other owls within a hundred yards or so (can you spot them?) The owls are there supposedly to discourage pigeons; there are other anti-pigeon measures along the road including spikes and netting. Owls will eat toads, by the way - I did check - though they're not their favourite food. But so far as I know owls do not eat beavers. The consensus of opinion is also that the plastic owls are not effective pigeon deterrents, or at least not for very long.

Pigeon spikes are also not always effective, especially when there's a parrot who disapproves of them:

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