96 The Naturalist in La Plata. 



in the sky, and the wave of terror attending its 

 progress subsides behind it, the birds still continue 

 wild and excited for some time, showing how 

 deeply they have been moved ; for, as a rule, fear 

 is exceedingly transitory in its effects on animals, 



I must, before concluding this part of my sub- 

 ject, mention another raptor, also a true falcon, 

 but differing from the peregrine in being exclusively 

 a marsh-hawk. In size it is nearly a third less 

 than the male peregrine, which it resembles in its 

 sharp wings and manner of flight, but its flight is 

 much more rapid. The whole plumage is uni- 

 formly of a dark grey colour. Unfortunately, 

 though I have observed it not fewer than a hun- 

 dred times, I have never been able to procure 

 a specimen, nor do I find that it is like any 

 American falcon already described ; so that for the 

 present it must remain nameless. Judging solely 

 from the effect produced by the appearance of this 

 hawk, it must be even more daring and destructive 

 than its larger relation, the peregrine. It flies at 

 a great height, and sometimes descends vertically 

 and with extraordinary velocity, the wings pro- 

 ducing a sound like a deep-toned horn. The sound 

 is doubtless produced at will, and is certainly less 

 advantageous to the hawk than to the birds it 

 pursues. No doubt it can afford to despise the 

 wing-power of its quarry; and I have sometimes 

 thought that it takes a tyrannous delight in wit- 

 nessing the consternation caused by its hollow 

 trumpeting sound. This may be only a fancy, but 

 some hawks do certainly take pleasure in pursuing 

 and striking birds when not seeking prey. The 



