Handbags   (The sad, the bad and the ugly. Non-productive stuff here.)

However, by the 1950s the entire UK blue tit population had learnt how to pierce the bottle tops to reach the cream, whereas the robins never did. Occasionally an individual robin learnt how to pierce the milk bottle seal but the skill never spread to the whole population as it did with blue tits.

Here

So them there robins aren't reliant after all.