64 The N aturalist in La Plata. 
was noon-day, had their crops full. There were 
three mice and two young cavies (Cavia australis) 
lying uiatouched in the nest. 
The short-eared owl is of a wandering disposi- 
tion, ard performs long journeys at all seasons of 
the year in search of districts where food is abun- 
dant ; and perhaps these winter-breeders came 
from a region where scarcity of prey, or some such 
cause, had prevented them from nesting at their 
usual time in summer. 
The gradual increase or decrease continually 
going on in many species about us is little re- 
marked ; but the sudden infrequent appearance in 
vast numbers of large and comparatively rare species 
is regarded by m.ost people as a very wonderful 
phenomenon, not easily explained. On the pampas, 
whenever grasshoppers, mice, frogs or crickets 
become excessively abundant we confidently look 
for the appearance of multitudes of the birds that 
prey on them. However obvious may be the cause 
of the first phenomenon — the sudden inordinate 
increase during a favourable year of a species 
always prolific — the attendant one always creates 
astonishment : For how, it is asked, do these large 
birds, seldom seen at other times, receive informa- 
tion in the distant regions they inhabit of an abun- 
dance of food in any particular locality ? Years 
have perhaps passed during which scarcely an indi- 
vidual of these kinds has been seen : all at once 
armies of the majestic white storks are seen con- 
spicuously marching about the plain in all direc- 
tions ; while the night air resounds with the 
