66 The Naturalist in La Plata. 
may be visible to the eye at a vastly greater dis- 
tance than during fair weather; the sun shining 
on its intense white plumage against the dark back- 
ground of a rain-cloud making it exceedingly con- 
spicuous. The fact that swans are almost always 
seen after rain shows only that they are almost 
always passing. 
Whenever we are visited by a dust-storm on the 
pampas myriads of hooded gulls—Larus maculipen- 
nis—appear flying before the dark dust-cloud, even 
when not a gull has been seen for months. Dust- 
storms are of rare occurrence, and come only after 
a long drought, and, the water-courses being all dry, 
the gulls cannot have been living in the region over 
which the storm passes. Yet in seasons of drought 
gulls must be continually passing by at a great 
height, seemg but not seen, except when driven 
together and forced towards the earth by the fury 
of the storm. 
By August (1873) the owls had vanished, and 
they had, indeed, good cause for leaving. The 
winter had been one of continued drought; the dry 
grass and herbage of the preceding year had been 
consumed by the cattle and wild animals, or had 
turned to dust, and with the disappearance of their 
food and cover the mice had ceased to be. The 
famine-stricken cats sneaked back to the house. 
It was pitiful to see the little burrowing owls ; 
for these birds, not having the powerful wings and 
prescient instincts of the vagrant Otus brachyotus, 
are compelled to face the poverty from which the 
others escape. Just as abundance had before made 
