204 CHALLENGER 



sight were logged and as the cruise progressed sub-arctic, sub- 

 tropical and tropical avian communities were encountered. There 

 are many seabirds which, unlike the coast-loving gulls, spend the 

 whole of their lives, except for the nesting season, at sea far 

 from land. Such are the Black-footed and Laysan Albatross which 

 attended the ship throughout her time in the North Pacific, al- 

 though they never followed Challenger west of the Nanpo Shoto 

 Islands which lie in a chain running southwards from the vicinity 

 of Tokyo Bay. The Black-footed Albatross were very numerous 

 and very curious. They insisted in clustering daily about the 

 wooden float which supported the i|-pound charge the scientists 

 drifted astern. When exploded, this charge gave a signal which 

 penetrated the sediment layer of the sea-bed, and returning after 

 the bottom echo, gave a thickness of the sediment on the ocean 

 floor beneath the ship. Despite considerable patience in waiting for 

 the birds to lose interest in the float it was sometimes necessary 

 to fire the charge while they still clustered round and inevitable 

 casualties resulted. 



There are three species of albatross known to the North Pacific 

 as against about a dozen species known in the Southern Hemi- 

 sphere. The birds have only been known to cross the Equator on 

 very rare occasions, and even these may have been carried across 

 as captives in ships, for they are fairly easily caught at sea with 

 a fishing line and hook baited with a piece of fat. The albatross, 

 like most other oceanic seabirds, is very susceptible to the 

 changing temperature of the sea, and does not follow a ship far 

 outside the zones of his preference. It is probably the type of 

 plankton food living in such waters that limits the bird's travel 

 rather than the change of sea water temperature itself. 



Oceanic birds can therefore be regarded as tell-tales for the 

 changes of temperature, and hence ocean current boundaries, thus 

 systematic watching of the birds while travelling across the oceans 

 forms a useful type of oceanographic observing. It is a pleasing 

 occupation to watch the petrels as they skim endlessly and effort- 

 lessly between and over the wave crests to windward of the ship 

 and to try and pick out this or that peculiarity of colour or profile 

 which will serve to identify the species. Alexander's Birds of the 

 Ocean, well thumbed and whitened with salt spray, lay to hand 

 on the bridge chart table. 



