300 Notes and Observations on a Guan. 



some species constantly, nest in trees. Sucli a nesting-place 

 doubtless lias only lately been resorted to — it is a reversion 

 to an ancient custom [italics ours] and not a survival, as in 

 the case of the Hoatzin." 



In the West Indies I am acquainted with the nesting- 

 habits of three Gannets. One of these, Sula piscator, invari- 

 ably nests in trees ; but two, viz. S. cyanops and S. sula, 

 invariably nest on the ground. Yet all three have helpless 

 naked young in the early stages of the nestling period ; and 

 it seems to me that it might just as well be argued that 

 originally all Gannets nested in trees ; that S. piscator has 

 never done anything else ; and that in the case of S. cyanops 

 and S. sula the descent to the ground has been of compara- 

 tively recent origin, consequent upon the more arid con- 

 ditions of their nesting-sites and a gradual and progressive 

 diminution of a lush vegetation in comparatively recent 

 geological periods. 



Knowing, as we do, of the far greater widespread 

 prevalence and luxuriance in past ages of the mangrove- 

 plants (Rhizophoracese) and mangrove associations — among 

 which S. piscator, tropical Cormorants, Frigate-birds, and 

 Pelicans seem to nest/or choice — I must confess that this last 

 argument appears as worthy of consideration as that which 

 supposes that the arboreal nesting-habit of -S. piscator is a 

 case of reversion. 



But perhaps we have said enough in support of our thesis 

 that in the life-history of the Guan we seem to have at least 

 illustrated among tree-nesting birds an intermediate and 

 living link in the chain of evolution of nidifugous habits, 

 which chain, as Mr. Pycraft has pointed out (Proc. IVth 

 Internat. Ornith. Congr. 1905), began on the one hand with 

 the reptilian method of progression seen in the young of the 

 Hoatzin, and ended on the other Avith the precocious poten- 

 tiality for flight (and a complete descent to the ground) as 

 seen in the case of the Megapode and its young. 



It may possibly be that some of the facts brought forward, 

 illustrative of the life-history of this most interesting and 

 primitive game-bird, could be interpreted in a contrary sense. 



