It might be the jays, they can be bullies, but it's unlikely that they are the cause of the death of the sparrows. The most likely situation is that there is a bad food source somewhere nearby. I'd suggest you take one of the birds to an Avian Vet, or find a wild animal rehab center that may be able to determine it's cause of death. Check with your local natural history, or bird watchers group, they may know of a disease amoung the sparrow populations. Your local university may have information, fish and wildlife.....

It may have an impact on other species of birds, including the jays, it may just be someone not cleaning their feeders and the food has gone mouldy, and the birds have injested this and died. If you have feeders, take them down, they may be infected with whatever has caused the death of the sparrows. Until you know, try to prevent other birds from being infected. Good luck.

Blue Jays are mean. They behave a lot like crows, and gang up on anything they may get interested in. They pester anything. I've seen a crow sneak in while the nest was unprotected and steal a sparrow. Either would do the deed.

Blue jays are MEAN . Im not sure how to get rid of them because they're so mean and persistent. You can try borrowing a friends cat for a while to roam around your yard. Thats how we got rid of our birds. But it will get rid of ALL your birds , the swallows might come back next meeting season though

I don't think it is the blue jays. I would be more likely to think that someone in my area was setting out poisoned food for the birds.

For the past three days, i found dead sparrows in my pond every morning. There is a tree above my pond where they must nest. We think blue jays we see everyday are attacking them and pushing them out of the tree into the pond. The sparrows seem to have no serious damage to them when we scoop them out of the pond. I love birds and all animals, what do i do? Its getting out of hand