AVES LARID^E. 209 



i 



fair weather, the sun shining on its snow-white plumage against the dark 

 background of a cloud rendering it very conspicuous. The fact of Swans 

 being seen almost always after a rain is only a proof that they are almost 

 always passing. Whenever we are visited by a great dust-storm, myriads 

 of Gulls appear flying before it ; this is invariably the case even when not 

 a Gull has been visible for months. A dust-storm is always preceded by 

 long drought, so that from the water courses being. all dry the Gulls 

 could not well have subsisted in the region over which it passes. Yet in 

 seasons of drought Gulls must be incessantly passing over us, visible only 

 when driven together and forced towards the earth by the violence of the 

 storm. The bird I allude to is the Black-headed Gull (Larus cirrho- 

 cephafas}. In seasons when Grasshoppers abound very much, flocks of 

 these birds also appear, often in such multitudes as to free entire districts 

 from the devastating swarms of the hated insects. It is a fine sight, and 

 a welcome as well, to see a flight of these birds settle on the afflicted 

 district ; at such times their mode of proceeding is often so regular, that 

 a body of them well deserves the appellation of 'an army of birds.' They 

 come down with a swift graceful flight, and settle on the earth with loud 

 joyful cries, but do not abandon when the work of devouring has begun 

 the order in which the flock was disposed. It often presents a front of 

 several thousand feet, with a breadth of but sixty or eighty ; all along this 

 line of battle the excited cries of the innumerable birds produce a loud, 

 incessant noise. Every bird is incessantly on the move some skimming 

 along the ground with half expanded wing, others pursuing the fugitives 

 through the air ; and all the time the hindmost birds are flying over the 

 flock and alighting in the front ranks ; so that the whole body is steadily 

 advancing, and leaving the earth over which it passes free from the pest. 

 The Black-headed Gull is one of our most common birds, and has many 

 very interesting habits ; I hope before long to make it the subject of 

 another letter." (Hudson, P. Z. S. 1870, p. 802.) 



At a meeting of the Zoological Society of London, 16 June, 1891, 

 "Mr. Howard Saunders exhibited and made remarks on some specimens 

 of eggs of the Spot-winged Gull (Larus maculipennis] and Trudeau's 

 Tern (Sterna trudeaui}, from the province of Buenos Ayres, obtained by 

 Mr. Ernest Gibson, F. Z. S., and believed to be exhibited for the first 

 time. The eggs of the former bird were, as might be expected, similar in 

 character to those of other marsh-breeding brown-capped Gulls. The 



