230 The Naturalist in La Plata. 
exercises that in bright warm weather, in winter 
and spring, it spends a great part of the day in the 
upper regions of the air. On the earth its air is 
grave and its motions measured and majestic, and 
it rises with immense labour, the wings producing 
a sound like a high wind. But as the bird mounts 
higher, sweeping round as it ascends, just as 
vultures and eagles do, it gradually appears to 
become more buoyant, describing each succeeding 
circle with increasing grace. I can only account 
for this magnificent flight, beginning so laboriously, 
by supposing that the bubble space under the skin 
becomes inflated with an air lhghter than atmo- 
spheric air, enabling a body so heavy with wings 
disproportionately short to float with such ease and 
evident enjoyment at the vast heights to which the 
bird ascends. The heavenward flight of a large 
bird is always a magnificent spectacle; that of the 
chakar is peculiarly fascinating on account of the 
resounding notes it sings while soarmg, and in 
which the bird seems to exult in its sublime power 
and freedom. 
I was once very much surprised at the behaviour 
of a couple of chakars during a thunderstorm. On 
a still sultry day in summer I was standing watch- 
ing masses of black cloud coming rapidly over the 
sky, while a hundred yards from me stood the two 
birds also apparently watching the approaching 
storm with interest. Presently the edge of the 
cloud touched the sun, and a twilight gloom fell on 
the earth. The very moment the sun disappeared 
the birds rose up and soon began singing their long- 
resounding notes, though it was loudly thundering 
