When people visit Switzerland for the first time, they look with great interest, not only at the mountains
but also at a type of clock-a Cuckoo-clock, on sale there. Cuckoo-clocks are very popular with tourists
looking for a souvenir. A Cuckoo-clock has a small painted cuckoo that comes out near the top of the clock
every half an hour and says, "Cuckoo". Every hour it comes out and says "Cuckoo" the right number of times.
It does not get a sore throat at midnight or mid-day! Children find these clocks wonderful. Adults gradually
get annoyed because the cuckoo never misses an hour or a half hour, and this makes a short sleep in an
armchair rather difficult.
In Europe, the cuckoo's call is a welcome sign that summer is on the way. This is the time when the
mother cuckoo flies round, looking for a nest (巢) to lay one of her eggs. She chooses a nest belonging to
another bird which already has eggs. When the nest is left unnoticed for a minute or two, the cuckoo rushes
down, lays an egg and hurries off. In this way, she may lay her eggs in as many as four different nests. not
one of which has been built by herself.
When a cuckoo egg hatches (孵化), the baby bird is bigger and stronger than the other nestlings. Step by
step, it pushes other baby birds and any unhatched eggs out of the nest. In this way, it receives all the food
from its foster-parents (养父母) and has a better chance of surviving.