132 NORTHERN ZOOLOGY. 



Lastly, the formation of the nostrils must not pass unobserved. One of the 

 typical characters of the Tyrant Shrikes is to have the aperture perfectly round, 

 or at least very nearly so ; and it is only among some small species of Tyrannulce 

 that the membrane is so far developed as to reduce this opening to a more oval 

 form : but in the Old World Muscicapaz the aperture is linear-oval, and in the 

 typical species linear. 



No satisfactory results have attended our attempts to draw characters from the 

 different modifications observed in the bills of these two races ; and, indeed, when 

 we see how completely this member differs in size, form, and thickness, in such 

 birds as Tyrannus crassirostris and intrepidus, or again in Savanna and audax, 

 we are convinced how futile will be all such attempts at present. The truth 

 appears to be, that almost every species, from our personal observations on these 

 birds, seems attached to certain species or genera of insects, which may be consi- 

 dered its peculiar food ; and these, varying in size and habits, are captured by 

 bills of different modifications. The whole of Tropical America may be said to 

 swarm with the Tyranninw ; so much so, that several individuals of three or four 

 species may be seen on the surrounding trees at the same moment, watching for 

 passing insects : each, however, looks out for its own peculiar prey, and does not 

 interfere with such as appear destined by nature for its stronger or more feeble 

 associates. It is only towards the termination of the rainy season, when myriads 

 of the Termites and Formica? emerge from the earth in their winged state, that 

 the whole family of Tyrants, of all sizes and species, commence a regular and 

 simultaneous attack upon the thousands which then spring from the ground. 



On duly weighing the peculiar distinctions of the small American Tyrants, we 

 feel justified in the suspicion that they do not belong to the same group as the 

 genuine Muscicapce ; while, on the other hand, these little birds are so blended 

 with the more typical Tyrants, that they can scarcely be detached from them even 

 as a genus. This will be manifest to any one who examines Tyrannus calcaratus, 

 ferox, and crinitus *, or Tyrannula Saya, querula, barbirostris, musica, or nigri- 

 cans t- The natural subdivisions of this group also require much investigation : 

 we can, indeed, feel little doubt that the typical genus is Tyrannus, and that the 

 T. crudelis* exhibits a greater perfection of structure than even the well-known 

 American Kingbird (T. intrepidus). Neither is it difficult to perceive that nature, 

 upon entering the group by means of Ptiliogonys, advances towards the Swallow- 

 tailed Tyrants by two different routes ; but one of these presents an hiatus, on its 



* Journal of the Royal Institution. f Philosoph. Magazine and Annals. June, 1827, P- 366. 



