ME. E. DEGEN ON ECDTSIS. 351 



III. — Method of Research. 



The practice commonly adopted for the study of the moult is that of observing the 

 changes on birds living in captivity. 



Confinement in cages and enclosures, however, as is well known, so greatly alters 

 the natural habits of birds that the information derived from this source is of too 

 uncertain a character to yield reliable results. 



As an instance of this contention, I have to mention only the frequent occurrence 

 of the adoption of the plumage of the male by old female birds deprived of the 

 opportunity of pairing. On this point Dr. Fatio (19) makes the following statement 

 (p. 269, I.e.): — "Moreover, anyone may have remarked that a bird which has been 

 kept in captivity, or which has been partially deprived of the normal influences acting 

 from without, never attains the perfection of its plumage so completely as the individual 

 which is in a state of freedom " (translation). 



Besides, there is abundant evidence for suspecting moult to be affected in those 

 species of birds which are of migratory habits. It is imperative, therefore, to take 

 into consideration the geographical range of such species when inquiring into the 

 subject. To show that this is the case with imported birds, I may quote the following 

 instances which came under my own observation : — 



A two-year old Cacatua roseiccipilla was transferred from Australia to London 

 during the months of October and November. It had just previous to departure 

 entered upon its regular annual moult, in accordance with conditions existing there ; 

 this continued during the voyage, and the process was finished at the end of January, 

 which is the normal course for this species. About the month of June, in the same year, 

 this bird, in accordance with the alternating season, entered upon another complete 

 moult, which it terminated in October following, thus undergoing two complete moults 

 (inclusive of flight- and tail-feathers each time) within one calendar year, a totally 

 unnatural proceeding. 



The other bird, a six-year old Parrot [Platycercus eximius), whose regular period 

 of annual moult in its native habitat is somewhat later, falling within the months of 

 December to March, on account of the wintry conditions prevailing here after its 

 arrival from Australia, suppressed this yearly process altogether till December of the 

 following year, which is the month corresponding with the regular conditions for this 

 moult in the southern hemisphere. Its plumage, on account of having been retained 

 for the two consecutive years, was consequently the worse for wear. (See also Bock (5), 

 p. 207, with remark by Dr. Cabanis.) 



From these incidents we derive the further information that the latter and older 

 bird adhered to the moulting-season prevailing for the Southern, whilst the former 

 and younger bird, immediately upon transfer, adopted that of the Northern 

 Hemisphere. 



