toll time / as fragile as a cuckoo's

[frindle]

Hello. I don't follow exactly what the underlined part means in this context.
1. Here 'toll' means 'sacrifice'?
2. I don't understand why a cuckoo has a fragile mind.
Please help. Thank you.


Here is the context. They are from a storybook about stolen Mona Lisa.

You must appreciate the risks I took in stealing the fair lady for Italy!
The secret I kept from the world, the months of unimaginable, the toll time took on nerves as jangled as a hummingbird's and a mind as fragile as a cuckoo's.

 

[Tdol]

If something takes a toll, it has a negative effect, causes damage, etc.

I don't know why the cuckoo's mind is fragile. Could it possibly refer to One Flew Over the Cuckoo's Nest? (Just guessing)

 

[frindle]

Thanks. But I still don't understand the second one, a mind as fragile as a cuckoo's.
Could it be related to the thing that cuckoos lay their eggs in other birds nests or something?

 

[Tdol]

But doesn't that show how clever the cuckoo is rather than being a sign of mental fragility? That's why I wondered about the book or movie, which does deal with mental health.

 

[frindle]

I agree with you. Thank you again.:-D