A Google Search led me to this quote regarding the problem of Common Buckthorn. It seems like wildlife food but some things are not as good as they appear.
Birds and mammals feed on buckthorn berries during the winter, aiding in the dispersal of seeds. While buckthorn may benefit from this behavior, the feeding animals do not. Buckthorn berries contain emodin, a natural laxative, that prevents mammals from digesting sugars found in the berries.
Just an FYI.