just found this site seems sme of you know a little sbout birds

Try and plant non-toxic types.

For the outside, plant something like Hops. Plant about 1-1.5 ft. away from the base of the pen. Provide something for them to climb up to 3.5 - 4 ft. before letting them attach to the wire. (prevents the birds from eating the tops)
Each fall carefully remove, down to the ground. They come back each year from the roots.
They grow really fast, and provide good cover for shade etc.

Inside you can plant Cedars etc. Try and find trees that will survive prunning. Plant 2-3 rows, about 1.5 - 2 ft. apart. Pheasants will use this for cover/shade etc.
The birds fertilize them.
I have used Brandon Cedar, Globe Cedar, Emerald Cedar.
I have Dogwood in two aviaries.
If you plant Junipers, make sure they are the non-berry producing ones (berries are toxic) or pick the berries off (takes 2-3 years for them to ripen).

Best to plant well before birds are in the pen. Any fresh dirt showing, and they'll dig it up.

Good mix of weeds, grass, clover or alfalfa for the main base.

You have many more options on what will grow in your area.
My being so far north, at the northern edge of growing zone 2b, limits what will grow for me.

I have Honeysuckle outside of one pen. Doesn't winter well at all.