BIRD LIFP] IN THE UEUBAMBA VALI.EY OF PERU. 53 



from Puno, but very near a Falkland Island bird. Additional 

 specimens, and particularly field studies, are needed to determine 

 satisfactorily the status of these herons on the table-land of Bolivia 

 and Peru, but the material examined in this connection (see list of 

 specimens under table of measurements) shows, as stated above, 

 the existence of a dark form in Chile and of a somewhat variable -^ 

 light form in the Falkland Islands and Argentina, and doubtless 

 Paraguay, Uruguay, and southern Brazil. The former has long 

 been known as Nycticorax cijanocepliahis, the latter has stood as 

 Nycticorax tayazu-guira until 1914, when Mr. Hartert,'* stating that 

 Paraguayan birds were referable to naevius, applied that name to 

 all the mainland birds east of the Andes and described the Falkland 

 Island bird as Nycticorax cyanocephalus falklandicus. 



I have no specimens from Paraguay, but it is not probable that 

 they M'ould differ materially from those in our excellent series from 

 northern Argentina. Some of the latter can be matched by dark 

 specimens of riaevius from the United States, nevertheless it is 

 quite evident that they belong to the form of naevius which inhabits 

 southern South America, east of the Andes, for which Vieillot's 

 name tayazu-guira, founded on Paraguay specimens through Azara, 

 is available. To this form I refer Falkland Island as well as 

 Titicaca and Lake Junin specimens. In other words, I follow 

 Sharpe ^^ rather than Hartert. As shown above, adults from the 

 FaUdands are essentially like adults from Peru, while an immature 

 Falkland bird can be matched by one from Jujuy, Argentina. In 

 other words, the Falkland Island bird can not be separated from the 

 light-colored mainland form either by color or by size. It is equally 

 clear that, in spite of its variability, there is but one light-colored 

 form of the Night Heron in southern South America, where it ranges 

 from at least Lake Junin to the Falkland Islands, specimens from 

 these two localities, as well as from Lake Titicaca being inseparable. 



The relationships of the light form (tayazu-guira) to the dark form 

 (cyanocephalus) are in doubt, but our specimens establish the fact 

 that both occur together on the Peruvian tableland, where also 

 intermediates between them are found. It is not impossible that 

 the dark coloration is a partial dichi'omatism, constant in Chile, oc- 

 casional on the tableland, and shown in a lesser degree by certain 

 specimens from Peru, Argentina, and the Falklands. Since %vritiDg 

 the above we have received an adult night heron from Panama, 

 which is nearly as dark as Chilean specimens. 



In size, the wing and tail average longer in the dark form. This 

 difference is well shown by the two males from La Raya, one of which 



2' Almost as much variation is shown by naevius in the United States. 

 -6 Bull. Brit. Orn. Club, vol. 35, 1914, p. 15. 

 " Cat. Birds Brit. Mus., vol. 26, pp. 155, 150. 



