CLOSED: Bluejay and Robin Interaction?

We currently have a Bluejay family with babies at the fledgling stage. With the neighbor's cat visiting quite often, the parents have gotten pretty noisy. The other day, we heard birdie distress sounds just before a pair of birds exploded out of the lilacs onto the lawn. A mature robin and a fledgling bluejay tumbled on the grass, and the robin moved to his tree. By that time, I'd run for my camera, and got several shots of this adorable baby and more shots of his concerned daddy as he looked on. This delightful photo op caused us to wonder this is normal behavior for robins. Our robin is damn near tame, and he comes quite close to us when we're sitting outside, so we were surprised to see this happen! Despite the fact that it gives me an excuse to share some sweet shots, I'm hoping some experienced birders can enlighten me about this aggressive behavior...

Did you know of the Blue Jays' habit of raiding nests for eggs and the very young? We try feeding the Jays' favorite food, peanuts, year round in hopes they will not bother other birds. But this year, our Kitchen Tree Robins must've had previous experience with Jays, so would not allow them any where near the feeders.

Our Robins are extra feisty this year, they have had knock down fights with the Brown Thrashers as well as other Robins. We've always seen the little territorial disputes but this is something else. I wonder if habitat loss is a reason for this.

Amazing. I did witness a flamboyant spectacle amongst the finches, but have never, ever seen our robins get feisty. The feeder is protected but the jays still poke their beaks through to nab sunflower seeds lying on the bottom. Thanks so much for your help!