296 Field Museum of Natural History — Zoology, Vol. IX. 



20. Larus Philadelphia (Ord). 

 Bonaparte's Gull. 

 Distr. : North America, breeding chiefly north of the United States ; 

 south in winter to the Gulf coast. 



Adult in summer: Bill, black; whole head, including throat, dark 

 sooty plumbeous; a white spot on the eyelids; back, pearl gray, 



shading into white at the base of the 



neck; under parts, white; feet, orange 



red; tail, white; first primary, white, 



with outer web and tip, black; second 



^ primary, white, tipped with black; 



rest of primaries with subterminal 



band of black tipped with white. 



Adult in winter: Similar, but 



Bonaparte's Gull. Summer. having the head and throat white, 



Bonaparte's Gull loses the black head in and the crown and sidcs of the head 



winter. 



showing more or less gray. 



Immature: Upper plumage mixed with more or less gray and pale 

 brown ; under parts, white ; tail with black band narrowly tipped with 

 white. 



Length 12.10 to 14; wing, about 10.25; bill, about 1.15. 



This species is abundant at times on Lake Michigan and in the 

 interior during the migrations in spring and fall. The majority arrive 

 from the south early in April. 



" Exceedingly abundant migrant. * * * In very mild winters a 

 few remain during the season." (Nelson.) "A transient migrant in 

 Illinois, occasionally wintering in the southern part of the state." 

 Ridgway.) "Winters along the Gulf of Mexico and southward and 

 sometimes in Illinois." (Cooke.) "The systematic slaughter of this 

 beautiful gull for millinery purposes has so reduced its numbers that 

 we can no longer claim it as our most abundant species." (Kumlien 

 and Hollister, Birds of Wisconsin, 1903, p. 11.) 



Genus XEMA Leach. 



21. Xema sabinii (Sab.). 

 Sabine's Gull. 

 Distr.: Arctic regions, south in winter occasionally to New York, 

 the Great Lakes, and Great Salt Lake. Stragglers have been taken 

 in Kansas, Iowa*, Bahama Islands, and Peru, S. A. 



* Dr. Paul Bartsch records two immature specimens taken near Burlington, Iowa. (The Auk, 

 Vol. xvi, 1899, p. 86.) 



