64 The Naturalist in La Plata. 



was noon-day, had their crops full. There were 

 three mice and two young cavies (Cavia australis) 

 lying untouched 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 mGst people as a very wonderful 

 phenomenon, not easily explained. On the pampas, 

 whenever grasshoppers, mice, frogs or cricket 

 become excessively abundant we confidently loo 

 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 ; Avhile the night air resounds with the 



