Its summer and birds should be flying round doing birdy things. However if your chimney pot does not have a birdguard type cowl on it they sometimes fall in and get stuck. We have rescued dozens of live birds (yay!) over the years and removed many more expired ones (boo!).
Rescue methods include the traditional grab and go to the more exotic where you can get the bird to hop onto a brush and push it up the chimney, we call it the sweeps elevator! Magpies, Pidgeons and Crows and Jackdaws are common but Owls sometimes find their way down too.
Prevention is key – if you dont have a birdguard fitted then consider getting it done, there are different types available and be aware not all are suitable for ‘live’ chimneys as they are designed for venting redundant ones.