Songbirds have good reason to fear white-tailed deer. Contrary to popular belief, deer are not vegetarians. Though they forage on plants they will eat eggs and baby birds when they encounter them. Some people have seen it. Trails cams show the rest of us.
Be alert when you hear a songbird freak out in the presence of deer. There’s a reason. Learn more and see a video in this vintage article: Deer Are Not Vegetarians.
(photos from Wikimedia Commons; click on the caption to see the original)