LIFE HISTOBIES OF WOBTH AMERICAN GULLS AND TEBNS. 151 



The postnuptial molt of adults, which is complete, occurs mainly 

 in July and August, though it is often prolonged into September. 

 Adults in the fall may be distinguished from young birds by being 

 somewhat lighter in color both above and below, with the gray of 

 the body plumage shading off gradually into the white of the head 

 and neck; in young birds this change is much more abrupt. The 

 head and neck are much whiter in old birds, with much less dusky 

 mottling, confined principally to the top and sides of the head. The 

 partial prenuptial molt begins in December, and by January or 

 February the pure white head of the nuptial plumage has been 

 acquired. The white tips of the primaries wear away partially or 

 wholly before spring, and the white tips of the rectrices also dis- 

 appear before the postnuptial molt. 



Food. — Although the food of Heermann's gull consists largely of 

 fish and other sea food, which it obtains offshore, it also indulges 

 freely in a great variety of other foods and does its part as a scaven- 

 ger along the shores and on the beaches with the other gulls, where 

 it does not seem to be at all fastidious as to its diet. Dr. George 

 Suckley (i860), however, says: 



This species, unlike the ring-billed and many other gulls, does not seem to 

 be fond of feeding on the shores and bare flats, but is almost always (in that 

 vicinity at least) found on the kelp beds floating in the deep water some 

 distance from shore. Whether they are attracted to these kelp beds by the 

 hopes of finding small shellfish in the upturned and netlike roots of such plants 

 as, detached from their fastenings on the bottom, have become entangled 

 together and with others in situ, or because these floating islands afford a con- 

 venient resting place where they can rest to a great extent secure from their 

 enemies of the land, I can not say ; but presume that the presence of a supply 

 of food must be a great inducement. 



Mr. A. W. Anthony (1906) describes their method of catching 

 fish as follows: 



When herring are swimming in compact schools near the surface both Heer- 

 mann's and western gulls secure them by approaching the school from behind 

 and flying near the surface of the water, making repeated, quick dips into the 

 school. The fish seek safety in the depths the instant anything occurs to alarm 

 them, but soon return to the surface, so that the gulls by stalking them from 

 the rear are enabled to approach quite near before the fish are alarmed. As 

 soon as the limits of the school have been passed the gull, rising higher in the 

 air, returns by a wide circuit and again passes over the school from the rear. 

 As the fish all swim in one direction, in a compact mass, these tactics afford the 

 gulls a decided advantage, which seems to be thoroughly understood. I think 

 that the Heermann's gull secures about one out of five fish that are snapped at 

 and the western half as many. Royal tern and the other gulls employ these 

 same methods but to a less extent. 



They have also been found to feed on shrimps and other crustaceans 

 and mollusca. 



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