Birdsbesafe Cat Collars protect your local songbirds from hunting by your housecat in most situations, but one of the situations that the bright collars don't overcome is when young birds leave the nests. Many songbirds leave the nest before they can actually fly.
These birds, the fledglings, spend a few days or so on the ground, trying out flying and learning to fly. At first, they are not yet really able to fly and if your cat tries to capture them then, your cat is likely to succeed. Birdsbesafe cat collars work by warning a bird to fly away -- which a fledgling may not be able to do.
So, if you want to go the extra mile to protect birds in your yard and environs, please ask your local birder friends or Audubon types, when songbirds fledge from their nests. It is usually a several week period, and after you know when it is, maybe you can keep your cat indoors for that time or at least severely limit their outdoor hunting time.
Try a harness to walk the cat? Later, you can rely on Birdsbesafe Cat Collars again to protect the birds.