146 NATURAL HISTORY OF BIRDS. 



with a fenestrated or closed labyrinth renders the character useless as such. As ex- 

 amples may be quoted the common eider, which has a labyrinth much like that of the 

 mallard, while it is feuestrated in /Sarkidiornis and JRhodonessa. Some species have, 

 in addition to the labyrinth, or alone, a bulbous expansion higher up on the trachea, 

 as in the rosy-billed duck (Metopiana peposaca) from South America, without lobe to 

 the hind-toe, and in the velvet-scotor (Oidemia fusca), one of our common sea-ducks. 



We shall now briefly review the minor groups into which this sub-family is divis- 

 ible, commencing with the tree-ducks, which seem to be -somewhat isolated, and, 

 perhaps, might have been made to form a separate sub-family in connection with the 

 Muscovy duck and the genus /Sarkidiornis. The tree-ducks (Dendroeygna) are 

 remarkable for their long thin neck, the long hind-toe, their arboreal habits, and their 

 curious geographical distribution. The genus consists of about a dozen forms, which 

 inhabit the tropical regions of the earth, chiefly America and the Malayan archipelago, 

 but also India, Madagascar, Africa, and Australia. This general distribution is not 

 so strange, since we have numerous parallels, as repeatedly observed on previous pages. 

 But in this case we are confronted with the fact that one species, D. viduata, occurs 

 both in Africa and in South America. Dr. Sclater, however, thinks it probable that 

 it has been introduced to the latter country by negro slaves, but we are not- aware that 

 this is more than a mere guess. The Muscovy duck (Cairina mosc/iata), originally 

 neotropical, but now domesticated nearly all over the earth, is too w r ell known to 

 detain us further, and the 'black-backed geese' (Sarkidiornis) need only be men- 

 tioned for the curious, compressed, high wattle, that surmounts the culmen for nearly 

 the whole of its length. The three species, one of which is found in South America, 

 one in South Africa and Madagascar, and one in India, are exceedingly alike, and 

 were once thought to be only one species, making one more instance of the kind of 

 geographical distribution alluded to above. 



Not very distantly related to the foregoing genera are the true sheldrakes, Tadorna, 

 of which the typical species ( T. tadorna) is well worth mentioning. Considering its 

 striking coloration, the head and neck being greenish black ; anterior part of back, 

 sides, and breast rusty brown, shoulders and middle of under parts black; wing- 

 speculum green, rusty brown behind ; bill and frontal knob bright carmine, legs flesh- 

 color, it will be perceived that it is one of the most striking-looking ducks. The size 

 is that of a mallard, but it stands higher on the legs, and looks much statelier and 

 walks better, on account of the more central position of the feet. The sheldrake 

 inhabits the coast of temperate Europe, and is also found in corresponding latitudes on 

 the eastern shores of the Palaearctic continent. It is sedentary, and, in spite of its 

 unlobed hind toe, is strictly confined to salt water. The plumage is only molted once 

 a year ; there are no seasonal changes, and both sexes are neai'ly alike in coloration. 

 Its breeding history is most interesting, for it nests in burrows made in the sand-dunes 

 of the coast, either made by themselves or other burrowing animals, as rabbits or foxes. 

 The inhabitants on several of the small sandy islands off the western coast of Jutland 

 notably the island of Sylt have made the whole colony of sheldrakes breeding there a 

 source of considerable income, by judiciously taxing the birds for eggs and down, 

 supplying them, in return, with burrows of easy access, and protecting them against all 

 kinds of injury. The construction of such a duck-burrow is described by Johann 

 Friedrich Naumann, who says that all the digging, with the exception of the entrance- 

 tunnel, is made from above. On top of a small, rounded hill covered with grass, the 

 breeding chambers are first dug out to a uniform depth of two to three feet. These 



