44 The Bird 



Mother Nature about the ground-nesters that she puts 

 strength and vigor into the coverts, or upper feathers on 

 the httle wings; so that these shoot forth with an energy 

 far beyond what is usual, for a time lending their aid in 

 flight, although they are not true primaries. Later the}' 



Fig. 27. — Iridescent feather from the breast of a Rufous Humming-bird, showing 

 wearing off of the tips of the barbs, caused perhaps by rubbing against the 

 petals of flowers. Magnified 25 diameters. 



are far outgrown by the flight primaries, and then func- 

 tion only as protectors of these more important feathers. 



The extreme in this precocious development of chicks 

 is found in those strange Australian birds, the mound- 

 builders, which are left from the first to shift for them- 

 selves; even the duties of incubation being shirked by 

 the parents. This necessitates a perfect ability on the 



