The pretty red berries of the American holly (Ilex opaca) can certainly look inviting. You might be tempted to taste them, especially after you see the birds gobbling them down. But remember that birds can tolerate poisons that would kill a human. Holly berries contain a number of toxins, and while fatalities are rare from holly consumption, there have been some documented deaths.
There may be no shortage of these shiny red berries in the fall and early winter in the eastern United States. Numerous native and non-native species of dogwood (Cornus spp.) can be found growing in the under story of forests or in transition zones between forest and field. The red berries of dogwood are eaten by birds, but should be avoided by people.