THE BIRDS OF NORTHERN THAILAND 133 



An immature tern in the Raffles Museum, taken by a Thai collector 

 at Chiang Mai in August 1936, is probably of this species and, if so, 

 is the only example from the Mae Ping above the rapids. At Chiang 

 Rai, on the Mae Kok, I observed at least eight individuals, May 6 and 

 7, 1936. Finally, it was found to be common on the Mae Khong near 

 Chiang Saen Kao, where I took four specimens on January 8, 1937. 



Our various terns have similar habits. They are seen in small flocks, 

 resting on sand bars or beating back and forth above the water, utter- 

 ing harsh cries and periodically plunging for fish. From gulls they 

 are distinguishable by their more buoyant flight, due to the long wings 

 and tail, and by their custom of keeping the pointed bill directed 

 straight down. 



The January birds from the Mae Khong, as well as two specimens 

 from the Mae Ping near Rahaeng (December 27, 1935), are adults in 

 full nuptial dress. 



The breeding adult has the crown and nape black, this color reaching 

 to below the eye and there edged by a streak of white; the upperparts 

 silvery gray ; the underparts very pale gray. Its nonbreeding plum- 

 age is much like that of the preceding species. 



This is the largest of our northern terns ; it has a very long, deeply 

 forked tail and a stout, orange-yellow bill. 



STERNA ACUTICAUDA J. E. Gray 



Black-bellied Tern 



Sterna acuticauda J. E. Gray, Illustrations of Indian zoology, vol. 1, No. 6, 1830- 

 1832 [=1831 ?], pi. 70, fig. 3 (Cawnpore, United Provinces, India). 



In the collection at Washington is an example of this tern, taken by 

 H. M. Smith on the Salwin near the Burmese village of Mae Hiak, 

 January 13, 1933. I collected three specimens on the Mae Khong at 

 Chiang Saen Kao, January 8 and 11, 1937, and another at Ban Mae 

 Sai, January of the same year. The only record for its occurrence on 

 the Mae Ping above the rapids is based upon a solitary individual seen 

 by me at Ban Chang (about 12 km. north of Mae Rim), June 6, 1936. 



All northern specimens examined have been in full nuptial plumage. 



Dr. Smith has noted that his bird, a male, had the bill dull orange 

 at the base, yellow at the tip ; the feet and toes light red ; the claws 

 black. 



The breeding adult has the crown and nape black ; the upperparts 

 silvery gray ; the sides of the head below the eye and the throat white, 

 this color changing to silvery gray on the upper breast, which color, 

 in turn, changes to black on the remaining underparts. The non- 

 breeding dress is similar to that of our other terns. 



This species somewhat resembles the whiskered tern, but may be 

 distinguished by its long and deeply forked tail. 



