At first,
while the babies are still blind, they can't see their mother at all.
They remain very still in the nest when she's not there so predators won't
notice them.
Q: How do baby hummers know when their mother has returned with
food? (Answer under photo.)
A.
They
can feel the wind from her wings on their skin, and they can hear the
little "mew" call she makes to them.