Blue jays are one of many types of birds that can be a nuisance in a residential setting. These birds are capable of pestering cats, dogs, and humans relentlessly by making threatening noises incessantly at a loud volume, as well as dive-bombing and pecking at humans and domestic animals in their own yards, each and every time someone steps foot out the door. A bird that behaves this way nearly always has a nest nearby and is protecting (rather enthusiastically) its young. After the baby birds leave the nest, the problem will likely resolve itself. In the meantime, you may try these tricks:
Determine the location in the yard where the bird is most likely to harass the cat. Try to pinpoint the location of the nest by observing where the bird comes from and goes to after each attack.
Remove any bird feeders from your yard, or hang them in areas that are as far away as possible from where your cat tends to hang out.
Place a plastic owl between the nest location and the typical location of the attacks on the cat. The plastic owl will appear to be a predator, which the bird will want to avoid.
Hang your shiny, fluttering objects in the same area as the owl. You might need to hang these objects in a perimeter around an area for the cat, attempting to make a buffer zone between the bird and the cat. The shiny objects will catch the sunlight and reflect it in an unpredictable manner, making it difficult for the bird to determine whether the object is a potential threat; therefore, the birds will wish to avoid them.