Maggie, we are losing our precious songbirds so anything we can do to protect them from any predator should be welcomed. If that was a female blackbird that was killed this morning then babies could now be starving in their nest. Spath, never mind the "little" bell, cat needs the loudest bell Gill can get.
Gill can I beg you to not let him out early on these summer mornings when the fledglings are still not street-wise and finding their way about. Keep him in until later when they have fed and had their fill, if you can. Thank you.