222 THE ODYSSEY OF AN ANIMAL COLLECTOR 
and honey and glucose, such as is a recognized diet for humming- 
birds in general, acted like a poison to these specialized feeders, 
and after having a good feed they looked miserably ill and I 
liberated them. I kept one for three weeks by completely changing 
the diet and was hopeful of solving the problem, but by that time 
the Sword-bills had completely disappeared as the brugmansia had 
finished flowering. Evidently they had gone to another district 
where, owing to different climatic conditions, these bushes were 
late in blooming. By changing about it seems that they can find 
their favorite food for most of the year. There is evidently some- 
thing different about the nectar of the brugmansia flowers for I 
never experienced any difficulty with artificial food for any other 
humming-birds. 
While here I was very interested in torpidity in humming-birds. 
At night at this altitude, when the temperature drops to around 
freezing point, these birds become torpid—a condition somewhat 
akin to that of a hibernating mammal, except that in the case of 
the humming-bird it endures merely for the night. As with 
reptiles, the temperature of the blood falls in keeping with that 
of the surrounding atmosphere, and respiration almost ceases. In 
this state a humming-bird can be picked up and has the appear- 
ance of being on the verge of death. Its tiny body feels frozen 
though it may give a feeble squeak when it is touched. Warmth 
will quickly revive it, but what is most astonishing is that this 
torpidity in humming-birds is something rhythmic, for on the 
coldest mornings when it is still freezing they come out of their 
torpidity at daybreak, so this is really a provision of nature to de- 
feat the effects of cold nights. The lowering of the blood tempera- 
ture means that less nourishment is required and so the bird sur- 
vives until the morning, when it can get sustenance in the form of 
nectar. Humming-birds in captivity go torpid very easily at the 
slightest lowering of temperature if they are not a hundred per 
cent fit, and then they have to be revived artificially. 
It is interesting that the only other birds in which torpidity has 
been observed are swifts, nightjars and colies (mousebirds), all of 
which show some relationship to the humming-bird. Once when I 
was in Natal I caught four colies and put them in an aviary. There 
a 
