12.To help make up for sleep lost during marathon night flights,migrating(遷徙) birds take hundreds of power nap(小睡) during the day,each lasting a few seconds.
Every autumn,Swainson's thrushes(畫眉) fly up to 3,000miles from their breeding grounds in northern Canada and Alaska to winter in Central and South America.Come spring,the birds make the long trip back.
The birds fly mostly at night and often for long hours at a time,leaving little time for sleep.So to get through these tiresome periods,thrushes,during autumn and spring when the birds are normally migrating,change their sleep patterns,staying awake at night and resting during day.But instead of sleeping for a long period at a time,the birds took several naps a day,each one lasting only 9seconds on average.
The thrushes also mixed up their shut-eye sessions with two other forms of sleep.In one,called unilateral eye closure,or UEC,the birds rested one eye and one half of their brains while their other eye and half brain remained open and active,protecting them from danger.
The birds also occasionally slipped into another state,one that any college student who has ever been stuck in a boring lecture can relate to.Called drownsiness(睡意),this state is characterized by a partial shutting of both eyes that still allows for some visual processing.
"In terms of quality,drowsiness may be less useful than normal sleep,but it may also be safer."said Fuchs.
What's interesting is that even animals should make up for sleep loss.That a need for sleep cannot be lost even in these birds means the importance of sleep for many,if not all,animals,not to mention human.
29.What would be the best title for the text?D
A.Migrating Birds Travel for Long Hours
B.Migrating Need Help
C.How Birds Migrate during Autumn
D.Migrating Birds Take Many Daily Power Naps
30.According to the text,when having drowsiness,the thrushesC.
A.will rest one eye and the other active
B.will often sleep during day
C.will still be careful with the possible dangers
D.will not see anything in front of them
31.What can we learn from the text?A
A.Sleep is important for human being.
B.Animals need sleep to rest.
C.Migrating birds need sleep only during day.
D.College students often have drowsiness in fall.