LIFE HISTORIES OF NORTH AMERICAN GULLS AND TERNS. 177 



showing the four extremes measure 54 by 37, 50.6 by 38.2, 44.5 by 

 35, and 47 by 32.5 millimeters. 



Plumages. — I have never seen the downy young of the Bonaparte's 

 gull, but Dr. Jonathan Dwight (1901) describes it as "much like 

 that of Sterna Mrundo^ yellowish with dusky mottling above." He 

 describes the juvenal plumage as follows: 



The upper surface is decidedly brown, with paler edgings ; a blackish brown 

 band extends along the cubital border of the wing into the tertiaries ; the 

 secondaries have dusky markings ; the primaries show little white, their coverts 

 being partly black, and the tail is white with a broad subterminal black band, 

 the recjtrices being tipped with buff. The sides of the head are white with a 

 dull black auricular patch and an anteorbital spot, and the rest of the lower 

 parts are white with a brownish wash on the sides of the neck and breast. 

 The bill and feet are black. 



This plumage is partially replaced, in September and October, by 

 the first winter plumage, the molt involving only the contour 

 feathers. " A blue-gray mantle and paler head are assumed," but 

 the wings and tail of the juvenal plumage are retained. A jDartial 

 prenuptial molt, involving mainly the head and neck, possibly some 

 of the body plumage, takes place during March and April. At this 

 molt most specimens merely renew the first winter plumage on the 

 head, but some birds acquire a partially black head. In some birds 

 the head is only slightly mottled above, but in others the deep plum- 

 beous hood of the adult nuptial is more or less complete. Young 

 birds can always be readily distinguished, even at a distance, by the 

 broad, dusky, subterminal band on the tail and by the color pattern 

 of the wings. The dusky cubital band is always in evidence, though 

 often much faded, in the lesser wing-coverts. The scapulars are 

 largely dusky, the greater wing-coverts partly so, and all the remiges 

 are broadly tipped with dusky. The three outer primaries are also 

 dusky on the outer web and for a narrow space on the inner web, next 

 to the shaft, on the outer two. 



A complete postnuptial molt occurs in summer, beginning in 

 July or August and lasting sometimes until October, at which the 

 adult winter plumage is assumed, with the pure white tail and the 

 white, black-tipped primaries. Adults have a partial prenuptial 

 molt, as in young birds, and a complete postnuptial molt in sum- 

 mer. I have examined adults in full winter plumage as late as 

 March 17 and molting into nuptial plumage at various dates from 

 March 30 to May 15. I have seen specimens taken on the Pacific 

 coast in full nuptial plumage on November 6 and December 2, but 

 ordinarily the postnuptial molt begins in August and is completed 

 in October; usually the flight feathers are molted last. 



Food. — Like its larger relative, the Franklin's gull, the Bonaparte's 

 gull is largely insectivorous. Over the marshy ponds of the interior 



