Timid and shy Robins?

Morning all,

I moved to my new home early Jan and with its expansive gardens close to woodland/farmland there has always been quite a bit of bird activity which is lovely - Coal Tits, Blue Tits, Sparrows and of course with 2 robins. Until last month, the robins were very much "in charge" and quite active at the bird eater and while they chased away any 3rd robin there was never any issues between the Tits and the Robins - they shared food with no issues and given the dexterity of the tits, and the fact they arn't shy, all got a fair share of any bird feed I put out.

However, over recent weeks I've noticed the Robins becoming a lot more docile towards the Tits and the robins flying away from the feeder when a Tit approaches - the Tits dont attack or anything, they just fly up and the Robins fly away and wait in a tree until the feeder is free. If i get the attention of a Robin and put out some mealworms away from the feeder they take the worms until the Tits find it and then back off.

There are about 5 or 6 tits in the garden. I'm surprised the change in behaviour - can anybody advise why? The robins do eat when they can, although perhaps not as vigorously as before - perhaps because there is plenty of other food this time of year? Do they feel outnumbered? 

I'm fascinated by this! In other respects the Robins appear fine - plenty of chirping and they otherwise appear healthy but they are a lot more timid!