Poison oak produces small clusters of berries that you can still see drooping from the stems. Over the last couple of weeks as I have walked around bird watching, I have frequently observed chickadees zipping in and out of poison oak patches gleaning berries. They usually pluck one and fly over to a near by branch. They don’t eat it whole. They hold it down against the branch with their feet and open it up. It appears that they are eating the fleshy part of the berry, and I imagine they ingest a few of the seeds too.
Poison oak loves living in disturbed areas, especially old farms like Mt. Pisgah Arboretum. I have heard poison oak referred to as the “protector plant.” It protects areas that have been disturbed so that they can heal. So it is no surprise that poison oak is an established plant of the ecosystem there. I am really allergic to poison oak, so it certainly keeps me out of certain areas and reminds me to try to minimize my impact on the environment.