Our large heated greenhouse has the front door open during mild weather. We occasionally have sparrows visit for a short time and in the spring hummingbirds love to come in to sip from the petunia flowers. If they get trapped there is plenty of water and food until the door is again open and they are released. Last week during a teacher workshop I was giving tours and a large bird flew in which I assumed was a curious seagull looking for compost scraps. The big bird made several swoops around the greenhouse (with teachers ducking) before we realized it was a red tail hawk. We have no idea what she was chasing but it made for a great tour!