Correlation 
habits of the White-rumped Swallow ( Zachycineta 
leucorrhoa) given by Mr W. H. Hudson on p. 32 
of Argentine Ornithology. He says that no 
matter how many nesting sites are available, 
there is always much fighting amongst these 
birds for the best places. ‘“ Most vindictively,” 
he writes, “do the little things clutch each other, 
and fall to the earth twenty times an hour, where 
they often remain struggling for a long time, 
heedless of the screams of alarm their fellows set 
up above them ; for often, while they thus lie on 
the ground punishing each other, they fall an 
easy prey to some wily pussy who has made her- 
self acquainted with their habits.” 
We have already emphasised the importance 
to many species of possessing the power of resist- 
ing the effects of damp. In the case of some 
organisms favourable variations in this direction 
may possess a greater survival value than those 
in the shape of greater speed or physical strength. 
Now, if there be any correlation between the 
power of resisting damp and the colour an animal 
bears, it is quite probable that animals of this 
colour, whether or no it be conspicuous, are likely 
to survive in preference to those who are more 
protectively coloured. There is some evidence 
that in certain cases, at any rate, resistance to 
climate is correlated with colour peculiarities. 
For example, some fanciers assert that yellow- 
legged poultry resist cold and damp better than 
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