ART. 18 PARASITIC HABIT IN DUCKS FRIEDMANN 6 



posed Rosy-bill eggs are identical with a mature egg which was taken from 

 the oviduct of a female of the Black-headed Duck. It may be remarked in 

 this counection that the Black-headed Ducks are not uncommonly seen in the 

 company of Coots. 



Since the time this was published, a few additional data have been 

 forthcoming, all of which tend to show that Heteronetta is regularly 

 parasitic in its breeding habits. It lays a relatively large ^gg for its 

 size, usually larger than the eggs among which its own are deposited. 



Of all the nonparasitic forms, the ruddy ducks {Eris7natura or 

 Oxyura) are certainly the most frequent offenders, and it is of great 

 interest and suggestive value that, for their body size, they lay the 

 largest eggs of any of the ducks except Heteronetta, which lays a 

 similarly large egg. At first sight it might seem that the large size 

 of the eggs, as compared with the smaller ones of the other ducks in 

 whose nests they are laid, is a factor directly correlated with the rela- 

 tively greater frequency of parasitism in the ruddy ducks, parallel- 

 ing in a way the case of the cowbirds parasitizing birds smaller than 

 themselves; but while the facts are perfectly sound, the correlation 

 appears to be only an indirect one. Ruddy ducks are notoriously 

 shy at their nests ; this is true not only of the North American species 

 Erismatura jamaicensis, but of the Old World forms as well. In 

 fact, so marked is this trait in the Palearctic Erismatura leucoceyhala 

 that there are many stories to the effect that the bird sits on the eggs 

 for a few days only, and that after the embryos have gotten well 

 started in their development the parent ceases incubation entirely 

 and actually does not even revisit the nest. 



Phillips -^ writes that Icucocephala occasionally uses old nests of 

 coots, thus sometimes not building for itself. Of the North Ameri- 

 can ruddy duck he records some very significant facts. The birds do 

 not mate early, or, at least, often not until after reaching their breed- 

 ing grounds. Some of the nests are — 



* * * very poorly constructed and in some cases the eggs have actually 

 been found wet in a carelessly made nest * * *. 



Another curious thing about the Ruddy is that not all the eggs found are in 

 the same stage of incubation and it is certain that the females lay more or 

 less in each others' nest, for their nests are often rather close together * • *. 



As a general thing so shy is the female that she is never seen near the nest 

 at all, even when the eggs are well along in incubation * * *. 



* * * The male retains some little pride in his own or other families 

 (we hardly know which) and is seen with the young broods until they are a 

 third or half grown, behaving in a most gallant fashion, displaying on any or 

 every occasion and rushing at real or imaginai-y intruders with a great show 

 of jealousy. He is therefore wholly an exception to any other North American 

 duck (excepting only the Tree Ducks) for he goes into molt much later than 

 any other species and spends the summer parading about in the full glory of 

 his rich, red plumage. 



• Natural history of the ducks, vol. 4, p. 156, 1926. 



