Hi Suzy and welcome to the Community. I also get lots of House Sparrows and Starlings in my garden and I do see mixed flocks of them quite regularly. I suspect that due to the Sparrows and Starlings being social birds by nature that it's quite normal for them to move together from one feeding area to the next. I often see a similar type of behaviour with the Jackdaws and Rooks, both of them once again being social birds. I hope this may help you.
Paul
My bird photos HERE
I’m having the same experience right now. I’ve seen the same single starling for multiple days and hanging out with the 20+ house sparrows that live in my yard. Is this common? I haven’t seen any other starlings around this season.
I have sparrows feeding on and off all day in my garden as they live in the eves of the flat above mine. Local starlings drop in and are often fighting amongst themselves to dominate access to the feeders . The sparrows tend to fly off or step back when the starlings arrive and I dont blame them!. A minority of starlings will feed more quietly alongside the sparrows .
I see it on a regular basis but i think it maybe the fact that the are both numerous & regular & they just seem to tolerate each other. The sparrows only give way if a starling tries to land in exactly the same spot. But if there are Starlings I always see sparrows there as well, maybe they enjoy the shark like feeding frenzy atmosphere, i know most of the other birds aren't too keen.