NUMERICAL EATIO. 121 



chosen, the paucity of human population in the 

 regions or districts which most species affect 

 and the little attention paid to them, even when 

 noticed, except by European collectors, tend 

 greatly to their exemption from molestation. 

 Perhaps more birds' nests are despoiled in one 

 year in England, than are those of the collective 

 group of Humming-birds in several seasons. 

 Hence, their nests are much rarer in cabinets 

 than might be expected from the number of 

 species therein contained. Probably most spe- 

 cies breed at least twice during the season, and 

 on the average, in ninety-nine cases out of the 

 hundred, in safety. Putting, then, these things 

 together, the numerical abundance of the Tro- 

 chilidce in their respective localities, each species 

 having its dilecta sedes, may, we think, be not 

 unreasonably accounted for, as well as the per- 

 petuation of this abundance in spite of losses by 

 man, by casualties, and also by natural death.* 

 With respect to the ordinary duration of the 

 life of these birds, nothing has been ascertained; 

 nor have we any data by which to form a con- 

 jecture ; we only know that the young males do 



* According to Mr. Hill, the Grey Petchary of Jamaica 

 and other islands, a species of Tyrant Fly catcher ( Tyrannus 

 Dominicensis), is known not unfrequently to make the 

 Humming-birds its prey, darting upon them as they hover 

 over the hlossoms of the garden. When this fierce hird 

 has seized a victim he kills it by repeated blows, struck on 

 the branch, where he devours it. 



