156 THE STORY OF THE BIRDS: 
The Goose-duck groups sleep sometimes floating 
on water, often squatting at its edge. Sometimes 
they may squat simply on the feeding ground in 
fields, but usually they have favorite couches, at least 
during the winter season, to which they will travel— 
often after dark—as much as a hundred miles, coming 
back next day to a favorite larder. There are some 
exceptions to these methods. 
The plovers sleep variously, but all out of trees of 
course. The waders generally sleep standing—usually 
on one leg, since one is found often much stronger 
than the other. Some are said to have a locking 
mechanism to prevent the joint bending while asleep. 
Storks, however, rest in a squatting position at times. 
Many ducks and geese also rest standing on one foot 
with the head under the wing. There can be little 
doubt that many of these birds have sentinels that 
watch while others sleep. All birds, however, are 
light sleepers and are apt to ery out or fly at the least 
sien of danger. 
The birds of prey have the peculiarity of roosting 
standing on both feet, never allowing the body to 
touch the perch. In the great capacity of their ten- 
don arrangement for grasping, a crouch brings, per- 
haps, a painful tension on their toes, or they may in- 
herit their standing tendencies from heronlike ances- 
tors. Most birds above them in the Picarian group 
(that perch) have the breast down, and all the Passeres 
roost thus. Near the fowl forms (practicing this) is 
that singular bird so frequently mentioned, the hoaetzin 
(pronounced wah-zeen) of South America, which is 
