Tidied around the bird bath

I had noticed a distinct lack of birds around the bird bath over the past couple of months. I do put fresh water in but it tends to get that black slime clinging to the concrete bowl. Also, the bushes around it had almost enveloped it so I expect the birds were feeling a bit trapped and vulnerable if they were enjoying a bath.
First thing I did was get the hedge cutter out and flatten the bushes by taking out all of the tops, leaving the two Lilacs either side (if I'd cut those off I wouldn't be typing this, I'd be buried beneath them!). I then got the scrubbing brush and cleaned the slime, which I think is mostly leaf mould from the Mayfower (Hawthorn) tree behind it. 
I'm thinking I'll have to carry the top bit, extremely heavy, into the garage and form a plastic lining. It would be much easier to keep clean, just have to find a thick bit of plastic big enough to do it in one piece.
The bird bath itself is very old. It was in my Uncles garden then it was passed to my father when he moved back down to Ledbury in the 80's and then we got it when he moved back to South Shields for a few years. They did come back to live with us when the dementia started to creep in, putting a plastic electric kettle on the gas stove was the last straw that made it an urgent matter of getting them down to our house in Gloucester.