;6 
NATURE NOTES 
thousands of rooks gather for the night. The bird roamed over a district of a 
ten miles radius, and was reported to me from several parishes. I think tliese 
facts establish the fact that cockatoos could be acclimatised in England at liberty, 
and would add much interest to country life if it were not for the barbarous silly 
fellows who will not let a strange bird live in peace. 
The Wren's Nest, Astwood Bank, James Hi.am. 
Worcestershire. 
Caged Robins. — I am .sure that the readers of N.atuke Noi'ES will agree 
with me here. .Vbout two weeks ago while in the neighbourhood of Finsbury 
Park, I was surprised to see in a bird dealer’s shop about half-a-dozen robins in 
a cage. Although the cage was roomy, it is not probable that the robins felt 
happy within their prison. Some of them were hopping about with wings almost 
touching the floor of the cage. Can anyone tell me if they have seen the same? 
It is the first time, and I hope the last, that I have seen our little friend as a 
caged bird. 
Canonbiuy. Ch.arles E. J. IIan'.nett. 
How do they do it ? — Now and then one comes across people who boast 
they have never changed their opinions in their lives ; and when we prove them 
these opinions generally turn out to be of little value. The study of Natural 
History has taught me many things, and amongst others that preconceived ideas 
must be surrendered with a light heart, and that what we know to be elementary 
principles of physics are apparently at times brushed aside in an astonishing and 
unexplained manner. 
It is an acknowledged law that an object floats if bulk for bulk it be lighter 
than water, and that the greater the disproportion the greater will be the weight 
or force required to cause submergence. 
Now the question arises. Do certain of our birds set this law at defiance ? Or 
do they possess some occult power as yet unknown to science ? 
.\lmost all diving birds have the power of submerging their bodies without 
any apparent muscular effort. The body sinks while the head and neck, or part 
of the bill, remains above the surface, and in this position it will remain a con- 
siderable time. During this almost complete submergence it is so absolutely still 
that not a ripple can be seen on the smoothest surface. This takes place irrespec- 
tive of the depth of the water or of the presence of weeds, or any matter to assist 
in keeping the bird in position ; in short, without any adventitious aid whatever. 
This action is not to be confounded with the habit of diving for food, which may 
be seen any day. In diving the body is placed in a nearly vertical position, and 
is then driven underneath the water by powerful strokes of the feet. In other 
words, diving is caused by the e.xpenditure of mechanical force, just as flying is 
attained by the use of the wings. 
All diving birds, when alive and undisturbed, as also do their carcases, float .‘o 
lightly on the water as scarcely to make any noticeable depression in it. In 
order, however, that a bird may submerge its body slowly without any apparent 
muscular effort, one would suppose it were necessary that its weight should be 
greater than the water it displaces, but how this is to be brought about it is 
impossible to suggest. Now a large specimen of the Great Northern Diver which 
weighs 15 lbs. may be said when totally immer.sed to displace about a cubic foot 
of water, and a cubic foot of sea water weighs 62 lbs., more than four times the 
weight of the bird. Consequently in order to keep the bird beneath the water a 
weight of 47 lbs. or an equivalent force would be required, and to suppose that it 
had the power of compressing its body to less than a fourth of its size, in order to 
equal the weight of the water displaced, is contrary to the evidence of one's 
senses and quite impossible. Nor is it conceivable that a sufficient volume of 
water could he received into the body to redress the inequality in weight. 
A dabchick has been seen to remain with only its beak protruding in a pond, 
and had selected some shavings about an inch long on the surface of the water, by 
means of which it for a long time escaped notice. The water was still and deep, 
and there were no weeds or such-like to which the bird could hold on with its 
feet. 
Heinrich Gatke tells us he saw a cormorant perform the following feat in 
a pond at the Zoological Gardens in Hamburg. A number of swallows were 
