In past years, the Ilex v. berries, both wild and planted, would be among the last to go here, if they were even eaten. This year, they disappeared before the weather turned cold.
I had a hermit thrush working one bush this year, which tells you how early they disappeared.

I also have several types of I. verticillata. The birds always ignored them until this year, especially Wintergold. Every berry is gone this year. The only ilex types that still hold berries is the blue holly - Blue Princess and an I. verticillata x I. serrata cross which is either Sparkleberry or Bonfire. Even the pyracantha berries are gone.
Are your shrubs large enough to perch on?

I have no suggestion as to how to handle the negative appearance of the unclaimed berries. Emerging Spring leaves may just shove them off the branches. My adventures with my one large winterberry have been reported in other forums, but, briefly, large flocks of robins must swing through a great part of S. Jersey, the native Ilex opaca holly being one of the commonest understory tree locally. This year they totalled my first major crop of berries on my one winterberry, ignoring the other holly type. That was in late September. Since, all berries are gone on all trees.
I, actually, plan to put bird netting on my Ilex verticillata until after Christmas, next year. One or two hermit thrushes are always wintering here, but their only impact seems to be an early feasting on the beautyberries on my little bushes. The big winterberry had so many berries, only the horde of robins could handle them.

Well, the shrubs are only about 30 inches tall so maybe they're too small for them to perch on. But thanks for your feedback. I was so looking forward to watching the birds have at the berries. Maybe next year. Thanks all!

Like I said, it took a few years for the birds to discover the feast I was growing for them in my yard. I have to admit though, I am a little disappointed as I choose shrubs that were suppose to have persistent berries in winter and they didn't make it this year past fall. I want the birds to eat the berries but I want to look at them a little longer too. Oh well.
I have a few theories about why the birds finally ate my offerings this year. One is, that most of my shrubs have matured enough to provide cover and are strong enough to perch on now? Maybe the long cool fall provided better tasting berries? Maybe they are building so much that food is more scarce?
Don't give up. "If you build it and they will come".