Crows nest

I think it's a madness of gardeners.

 

Thanks everyone for the helpful suggestions. I have bought some smoke pellets and tried that, fun but no success. The rifle, gosh I am tempted but I wouldn't honestly have the heart to do it. The detonators too sound fun, but I do want a chimney left!
I was a bit perplexed about what the birds were as I couldn't find the call online. Once Kandy said Jackdaws, I checked that and you are spot on. I thought they were a bit small for crows. Thanks for that.
I am going to give it a few days and then probably call the sweep to sort it.

I have checked online and Jackdaws should be nesting in April, what with the warm weather perhaps they are starting early. One thing that is a bit worrying is what looks like bits of mortary lining rubble that comes down occasionally.

Thanks everyone, really helpful.