26 



NORTH AMERICAN FAUNA. 



like those from western Mexico. Specimens from Ascension Island, off 

 the west coast of Africa, also have a light ashy shade on the lower 

 tail coverts. 



The following average measurements show the sizes of these birds 

 from various parts of their range : 



Table of measurements of Sterna fuliginosus and Sterna f. crissalis.* 



* All measurements are in millimeters. 



In the foregoing measurements the length of the tail is unreliable, 

 owing to its variability, on account of wear and other causes. 



Anous stolidus ridgwayi Anthony. Pacific Noddy Tern. 



Anous stolidus Lawr., Mem. Boston Soc. Nat. Hist., II, p. 318, 1874. 

 Anous stolidus ridgwayi Anthony, Auk, XII, p. 36, 1898. 



Common the last of April on Isabel Island, and a few seen off the 

 Tres Marias during May. Between San Bias and the islands a 

 number of these birds were seen. We usually saw one or two indi- 

 viduals at a time, and did not find them in flocks anywhere except 

 when congregated on the rocks at their roosting places. At sea they 

 usually flew close along the surface of the waves with long, graceful 

 wing strokes. From their dark color and habit of keeping close to the 

 water they were several times mistaken for black petrels. 



They were found in considerable numbers on the ragged faces of 

 cliffs and rocks along the northeastern point of Isabel Island, and were 

 very unsuspicious, permitting us to approach quite near in the boat. 

 While perched on the black lava cliffs, their dark color blended so 

 closely with the background that it was very difficult to distinguish 

 them, even when within fair gunshot. The day we left the island we 

 visited their resting place and fired a dozen or more shots while they 

 were on the rocks or flying about, but the noise of the reports did not 

 seem to give them much alarm. They would circle out a short dis- 

 tance, and, after hovering for a few moments over their killed or 

 wounded companions floating in the water, would return to the same 

 part of the cliff from which they had just been startled. They were 

 not heard to utter any notes, and the silence with which they would 

 suddenly appear out of the cliff and then return and vanish again in 

 its gloomy face produced an uncanny effect. 



