If so, the animal needs immediate intervention. Don't approach an injured wild animal without calling a professional for advice. This is not a reliable rule of thumb. For example, it is not unusual for female rabbits to leave their bunnies alone in the nest or when a bit older, alone above ground during the day. The bunnies stay put and wait for mom to return at dusk from foraging for food.
Deer show similar behavior.
If you're lucky enough to locate and have access to the nest, and if the baby bird doesn't seem injured, put her back. It's a myth that parents will abandon the baby bird once they smell human scent on them. Every year, thousands of wild animals are injured or orphaned as a result of human activities. Their legs are broken by fishing line, their wings are fractured after colliding with a car. They sustain head trauma from hitting windows and are poisoned after eating insects and plants treated with pesticides and herbicides.