FAMILY LARIDAE 453 



November, and the return northward is mainly in April. Numbers 

 of nonbreeding individuals, in immature (or winter) plumage, re- 

 main through the months of northern summer. In 1953, on June 

 11, I collected one on the lower Rio San Pablo, near Guarumal in 

 southern Veraguas. Others were recorded later in this month at 

 Riomar, Playa Coronado, and Nueva Gorgona along the Pacific 

 coast and on the Rio Chagres above Gamboa in the Caribbean drain- 

 age. Eisenmann (Condor, 1957, p. 252) recorded them in Almirante 

 Bay, Bocas del Toro, June 29, 1956. There are numerous other sum- 

 mer records. These terns range regularly through Gatun Lake, and 

 less commonly over the broad reaches of the Chagres between Gam- 

 boa and Juan Mina. 



In 32 records for Panama of birds banded on their northern nest- 

 ing grounds the majority were marked in Ontario, with others from 

 Michigan, Wisconsin, Minnesota and Illinois. Only four came from 

 east coast colonies in Massachusetts, New York and Maryland. Of 

 the total returns 30 are of birds that died during their first winter. 



Common terns range alone or in small groups, usually in flight 

 a few meters above the water, which they scan with bills pointed 

 downward. When small fishes appear they dive instantly in attempt 

 to seize them. Near Isla Taboga in December I have recorded flocks 

 of 30 to 40 resting in company on calm water, and off the Balboa 

 entrance of the Canal I have seen 20 or more crowded together on 

 the base of a buoy. Near Punta Mala I have observed one in com- 

 pany with black terns, resting on a stick of driftwood 5 kilometers 

 or so offshore. And in Almirante Bay I have seen them with royal 

 terns standing on snags stranded in shallow water. One that I shot 

 here February 20, 1958, was in very badly worn plumage on the 

 wing coverts and the whole upper surface. 



[It is probable that Sterna paradisaea Pontoppidan, the Arctic tern, 

 gaviotin drtico, which includes the eastern Pacific in its migrations 

 from northern breeding grounds may come casually into offshore 

 Panamanian waters. The nearest record to date is an adult female 

 in the British Museum (Natural History) taken during the St, 

 George Expedition on October 4, 1924, "at sea 300 m. S. of Panama." 

 As the ship was en route to Isla Gorgona this would have been ap- 

 proximately 200 kilometers from the coast of Colombia. The species 

 has been found in considerable numbers at sea off Peru and Chile, 

 and is reported casually on the coast of the latter country. 



The Arctic tern differs from the common tern in grayer color 

 on the ventral surface and in the shorter tarsus, which measures 

 13.5 to 16. mm.] 



