MOULT SAND PLUMAGES 23 



Another illustration of the completeness of the imitation of the 

 female plumage by some species, will be seen by reference to Plates 28 

 and 29, where it will be observed that the American Merganser, himself 

 without crest, assumes a crest, as in the female, during the eclipse. On 

 Plates 11 and 17, it will be seen that even the bills of some species change 

 colour, as illustrated on these Plates by the Gadwall and the Shoveller. 



The eclipse moult is peculiar to the Ducks, and is exhibited in no 

 other kind of bird. Strangely enough the eclipse is present only in the 

 ducks of the Northern Hemisphere, not being found in those of the 

 Southern Hemisphere, even in those countries where the climate is 

 similar to that of the North, and even in ducks of the same species, such 

 as the Cinnamon Teals of North and South America. 



Much variation exists in the extent of the eclipse moult. In some 

 species the change into the female-like dress is complete, as has been 

 described in the case of the Mallard and the American Merganser. In 

 others, the eclipse plumage more closely resembles the dress of the ju- 

 venile male. Yet again, it may be somewhat of a mixture of the female- 

 and juvenile-male-type dress. However, the appearance, in general, is 

 very much like that of the adult female. 



The eclipse is practically complete in all of the River and Pond 

 Ducks. It is less complete in the case of the Diving Ducks, in which 

 some traces of the winter plumage are retained. In those ducks in which 

 the sexes are very similar, such as the Black Ducks and the Scoters, it 

 is obvious that there can be no eclipse moult in the sense that "eclipse" 

 is a change into a more sombre, female-like plumage. In such cases there 

 is a partial prenuptial moult, and a complete postnuptial moult of both 

 sexes, during which very little seasonal change in plumage is apparent 

 (see eclipse plumage of Black Duck). 



There is great variation in the dates of the flightless period; in 

 general it would be safe to say that the flightless season for River and 

 Pond Ducks is between the first or second week in July and early 

 August; with Diving Ducks the peak of the flightless season is between 

 the last of July and the end of August. 



The Old-squaw and Ruddy Duck have distinct and different plu- 

 mages for both winter and summer. Some ornithologists claim that the 

 winter plumage of the Old-Squaw is its nuptial or breeding plumage, 

 and its summer plumage is really a prolonged eclipse plumage. It is also 

 held that the female-like winter plumage of the Ruddy is a prolonged 

 eclipse plumage. 



Whether the eclipse plumage represents a return to some primitive 

 ancestral plumage, in which the sexes were alike, or is a more recently 

 adopted, specialized development to render the male less conspicuous 

 during the flightless period, is a matter for discussion, even among 

 experts. Whatever the true explanation of the phenomenon of "eclipse" 

 may be, it remains a feature in which Ducks differ from all other classes 

 of birds. 



