HYBRIDISM 43 



Cackling Goose, 45-48 m.p.h. ground speed, by automobile. 



Brant, 45 m.p.h. air speed. 



Snow Goose, 50 m.p.h. (approx.) air speed, chased. 



Mallard, 46, 50, 55, 58, 60 m.p.h. air speeds. 



Pintail, 52 m.p.h. (approx.) ground speed, train. 



Pintail, 65 m.p.h. (approx.) air speed, chased. 



Shoveller, 47 m.p.h. ground speed, easy flight, automobile. 



Shoveller, 53 m.p.h. ground speed, easy flight, automobile. 



Redhead, 42 m.p.h. ground speed., train. 



Canvas-back, 72 m.p.h. (approx.) air speed, chased. 



Golden-eye, 50 m.p.h. ground speed, train. 



The flight speed of a bird flying directly against or directly with the 

 wind is that of its speed due to its own exertions (its air speed) minus 

 or plus the exact speed of the hindering or favouring wind. For exam- 

 ple, if a bird is flying at an air speed of 40 miles per hour directly with 

 a wind of 30 miles per hour, the ground speed of the bird is 70 miles 

 per hour. If the same air speed were being made directly into a head 

 wind of 30 miles per hour, the bird's ground speed would only be 10 

 miles per hour. 



The effect on the flight speed of a bird, of side winds from varying 

 angles to its line of flight, is dealt with in an interesting and comprehen- 

 sive article by Francis H. Allen, in the Auk of July, 1939, to which the 

 reader is referred. 



HYBRIDISM 



Ducks, Geese, and Swans, like all other birds and mammals, usually 

 pair with others of their own kind. Occasionally, however, specimens 

 are found which are, unquestionably, the result of interbreeding be- 

 tween different species, different genera, or even between different sub- 

 families. Among the many strange hybrids recorded are crosses between 

 Swans and Geese, between River Ducks, Eiders, and Mergansers, and be- 

 tween Diving Ducks and Mergansers. 



The chances for crossing in a wild state are naturally greatest be- 

 tween closely related species whose breeding ranges overlap, and many 

 interesting wild hybrids are encountered. As might be expected, how- 

 ever, a far greater number of misalliances are reported in the mixed, 

 semi-domesticated flocks brought together from various regions and 

 maintained through successive breeding seasons in park lagoons or 

 zoological gardens, or confined in cages. The British Ornithologist's 

 Club (1929) exhibited over 125 hybrids obtained largely from such 

 sources. 



Of all members of this family the Mallard is the one which is more 

 often involved in crossing than any of the others. On this continent, the 

 wild Mallard crosses readily and repeatedly, not only with the closely 

 related Black Duck and with the Pintail, Baldpate, Shoveller, Green- 

 winged Teal, and Gad well of the same subfamily, but even with the 



