FAMILY RYNCHOPIDAE 465 



Females, wing 331-362 (342), tail 102.6-112.8 (108.4), culmen 

 51.8-64.8 (56.4), tarsus 26.6-33.7 (30.1) mm. 



Presumed to be migrant from the north. Casual in occurrence. 



Griscom (Ibis, 1935, p. 545, and also in his check-list) gives a 

 sight record for the Pacific coast of Veraguas, which must have been 

 made in the early part of 1924 during a trip out from the Wilcox 

 camp on the Rio San Lorenzo, west of the entrance of the Golfo de 

 Montijo. He refers also to "skimmers seen but not collected" by 

 Arce, a report that may have been a slip of the pen, as I have not 

 found any authority for such a record. 



In recent years nesting colonies of the black skimmer that have 

 been found on the western coast of Mexico, in Sonora, Sinaloa, and 

 Nayarit, are the evident source of the birds reported in the nonbreed- 

 ing season south to El Salvador. Griscom, on the basis of a small 

 series of these northern migrants taken on the coast of Guatemala, 

 described a race ohlita. Recent studies indicate that the Pacific popula- 

 tions do not differ from those of the Atlantic area so that the proposed 

 form is a synonym of typical nigra. 



RYNCHOPS NIGRA CINERASCENS Spix 



Rynchops cinerascens Spix, Avium Spec. Nov. Bras., pt. 2, 1825, p. 80, pi. 

 102. (Rio Amazonas, Brazil.) 



Characters. — Differs from typical nigra in lesser extent of the 

 white edgings on the ends of the secondaries ; tail, in adult, with dark 

 colors predominating, especially on the inner webs of the feathers; 

 under wing coverts neutral gray in the adult, sometimes almost white 

 in immature birds. 



Measurements.— UdXts, wing 380-416 (392), tail 111.5-130.3 

 (113.7), culmen 75.0-87.7 (86.6), tarsus 32.2-38.5 (34.8) mm. 



Females, wing 333-375 (353.7), tail 100.3-119.0 (108.8), culmen 

 59.4-66.8 (64.0), tarsus 28.4-31.5 (30.2) mm. 



Casual in occurrence on the Caribbean coast. 



A male in the American Museum of Natural History, taken by 

 R. R. Benson at Cocoplum, Bocas del Toro, October 28, 1927, is a 

 typical example of this race. Eugene Eisenmann has informed me 

 that on June 28, 1952, in company with John Bull he saw two 

 skimmers flying at Fort San Lorenzo on the mouth of the Rio 

 Chagres. These are the only records. 



The subspecies cinerascens of northern South America is common 

 on the larger rivers of northern Colombia including the Rio Atrato. 

 It is probable that these birds wander from time to time into 

 Panamanian waters. 



