5o6 A NATURALIST IN THE PACIFIC chap. 



The view naturally presents itself that in past ages birds in the 

 Pacific were much more uniform in their characters, and the agencies 

 of dispersal far more active in their operations and far more 

 general in their range than in more recent times, " It may be 

 accepted (says Mr. Dixon) as an axiom of geographical distribution 

 that all existing species are surviving relics of more ancient forms 

 or ancestral types, whose dispersal in a remoter past was more 

 continuous, and whose affinities and characteristics were therefore 

 more homogeneous." I assume that in past ages the differen- 

 tiation of birds has largely been favoured by differentiation of 

 climate acting through the limitation of their ranges. To these 

 changes, plants, so often biologically connected with birds, have 

 largely responded. 



There is, of course, no difficulty in imputing to birds the capacity 

 of reaching Hawaii in the mid-Pacific, and there are many regular 

 migrants now (sea-birds, waders, ducks, &c.). The only difficulty 

 is in the estimation of the time occupied in the trans-oceanic 

 journey. According to Gatke the journey, which is 1,500 to 2,000 

 miles, ought to be accomplished within the limit of fifteen hours, 

 which he regards as " the longest spell during which a bird is able 

 to remain on the wing without taking sustenance of any kind." 

 As he considers that a bird might cover the 1,600 miles between 

 Newfoundland and Ireland in nine hours {Heligoland as an Ornitho- 

 logical Observatory, p. 140), the Hawaiian traverse would offer to 

 him no difficulties. It has frequently occurred to me in this 

 connection that in ancient times, when the volcanoes of the mid- 

 Pacific were in full activity, their light at night-time would have 

 often given a direction to the migrating bird, and that they might 

 have sometimes determined the line of migration across the Pacific. 



It has not been possible to discuss here the capacity of pigeons 

 to cross an ocean, a subject bearing directly on the floras of all the 

 Pacific groups (excepting Hawaii, which possesses no indigenous 

 Columba;) and as concerning these islands generally presenting no 

 difficulty. Dr. H. de Varigny, who amongst his other studies has 

 long displayed an active interest in plant-dispersal, has directed 

 my attention to two very important papers on the flight of pigeons 

 in the Revue Scientifiqiie, one by M. A. Thauzies (April 30, 1898) 

 and the other by M. M. Dusolier (Nov. 28, 1903). That land birds, 

 as well as swimmers and waders, cross the Atlantic is well known, 

 and in this connection the reader might profitably consult Prof 

 YieWprms Geographical Distribtition of Aiiinials (vol. ^Z, Internal. 

 Sci. Ser. 1887). 



