Re: deer and winterberry. They are a high fat berry. Adult deer seem to ignore my berries (but browse the shoots later in the winter!!) But the years that twin fawns are born nearby, I have to set reminders to spray my winterberries proactively (Deer Off, Plantskydd). I’ve seen them stand on their hind legs to get at those high density winter calories, twigs and all. The shrubs are not a pretty sight after. . . and I thought they had finally grown above spring deer browsing height!

Re: birds eating winterberry in the fall, vs. on their return trip from points south, migrating robins ignored this “rule” in my garden, too, . . . until 2 years ago, when I had all the nearby barberry and buckthorn “shrubbery” bulldozed and buried. Now my winterberries no longer seem to be on their “migration itinerary”? Time will tell.

What you are describing is incomplete pollination for some reason — could be weather, or that the male isn’t large enough to have enough pollen for both females yet I suppose (typically you can have one male for a group of three to five females). Or just that it sounds as if the plants aren’t full grown yet.

I don’t know if this happened just the one year, or each year you’ve had them, and how small they are and so on. Next spring keep a watchful eye for when the tiny white flowers are produced on the females and notice whether the male has his flowers at the same time to make sure you have a good matchup.

By the way, a dryspell can make fruit abort before its fully grown/ripened. Last year it was dry here and the fruit fell off many of my plants’ branches, so it looked as if they hadn’t set fruit — they had, but just didn’t have the water they needed to ripen it.