24 BULLETIN 107, UNITED STATES NATIONAL MUSEUM. 
them in anything approaching a flock. Throughout the interior, 
where they are more numerous, they seem to fly in flocks. Audubon 
(1840) mentions a flock of 30 which alighted near him in a pond, and 
states that they migrate in flocks, flying high in the air and following — 
the courses of streams. 
The horned grebe swims buoyantly and rapidly, using its feet alter- 
nately; it also has the power of sinking below the surface and swim- 
ming with its body partially or wholly submerged and with only its 
bill protruding. Coues (1877) and some other observers seem to think 
that this is accomplished by so regulating its respiratory processes 
that its body is increased or decreased in bulk; he cites the following 
instance to illustrate it: 
Once holding a wounded grebe in my hand, I observed its whole body to swell 
with a labored inspiration. As the air permeated the interior, a sort of ripple 
or wave passed gradually along, puffing out the belly and raising the plumage 
as it advanced. With the expiration the reverse change occurred from the op- 
posite direction, and the bird visibly shrunk in dimensions, the skin fitting 
tightly and the feathers lying close, 
I have always supposed that grebes and some other water birds 
had the power of regulating their displacement, and consequently 
their floating and sinking ability, by their control of their plumage, 
compressing the feathers of the body to reduce the displacement and 
expanding them to increase it; the above incident, cited by Coues, 
seems to be open to this interpretation as well as any other. 
This grebe is just as good a diver as the rest of its tribe. Mr. E, 
Howard Eaton (1910) says: 
I have often seen it remain under water for three minutes and cover a 
distance of at least 30 rods at one drive. 
Dr. Charles W. Townsend (1905) has well described its diving 
power, as follows: 
The diving of this grebe is often a beautiful piece of work. The bird springs 
vigorously upward and forward, the bill cleaves the water on the downward 
curve just as the feet leave it, while the whole body describes an arc. The 
wings are closely applied to the sides, and do not flop out as in the Alcidae, 
where they are used for flight under water. In the grebes the feet are the 
propelling power in the forceful initial spring and in the movements below 
the water. That the wings are kept close to the sides under water I have been 
able to observe when the grebes were borne up in the advancing rollers on 
Ipswich Beach. The clear water before the waves broke revealed the diving 
birds. The full beginning of the dive, as described above, is often curtailed in 
all degrees, so that the head is below water before the feet emerge, or the jump 
is lost entirely, and the bird disappears suddenly with a vigorous kick, or 
mysteriously and quietly sinks in the water. The duration under water de- 
pends somewhat on its depth as well as on the abundance of food there. Thus 
a grebe close to the rocks stayed under from 30 to 35 seconds, while the same 
bird a short distance out was under water from 45 to 50 seconds each time. 
They often remain below the surface longer than this. 
