Thousands of starlings come here every winter, some from as far away as Russia. They come to escape the cold winters, and especially frozen ground. To feed, a starling sticks its beak in to the ground, and then opens it to make a hole.
A starling's eyes swivel to point forward so it can see if there's a tasty insect grub in the hole. But when the ground freezes a starling can't push its beak in. And even if it could, it would find that most of the grubs have dug themselves in that bit deeper to avoid the frost.
At this point, the starling switches to berries, seeds and grain. It's harder to digest these so the starling's gut grows longer in the winter to get the most out of its food.
View this page online at http://www.rspb.org.uk/youth/discover/birds/bird_food/starlings.asp