Birds inhabiting the Southern Ocean. 293 



however, is quite right when he says that sometimes a marked 

 bird turns up after being absent for two or three days; and 

 how can this be accounted for by the theory of the birds con- 

 stantly following the ship ? Most of the Petx'els, more particu- 

 larly those that burrow, or live in holes in rocks, are, no doubt, 

 nocturnal in their habits when they are on or near land ; but, 

 when they are at sea, they all become more diurnal. A few 

 can certainly be often seen flying under the stern at night ; and 

 once, when I was keeping the middle watch, at about one 

 o'clock A.M., a Cape-Pigeon, in crossing over the ship, struck a 

 rope and fell on deck. Still they are never numerous; and, 

 where there were fifty or a hundred birds in the daytime, there 

 are only one or two at night. 



Their defenceless condition is, as far as I can see, the only 

 reason for the Petrels hiding themselves by day, and flying by 

 night, for the oceanic Mollusca, &c., on which they feed, are 

 equally diurnal and nocturnal. At sea, however, where they 

 have no enemies to fear and no holes to hide in, the conditions 

 are quite difi*erent, and it is then better for them to take their 

 rest at night, and to be alert and feeding in the daytime, and 

 they change their habits accordingly. I, therefore, believe that, 

 although a few may follow a ship for a night, most of them 

 sleep on the sea, and in the morning, knowing very well that a 

 ship is the most likely place to obtain food, they fly high with 

 the intention of looking for one. Some find the ship that they 

 were with the day before; some another one. In the latter 

 case, if the second ship is going in an opposite direction to the 

 first, they are never seen by the first again ; if, however, the 

 course of the two ships is the same, the bird might very likely 

 lose the second ship and rejoin the first, after a lapse of two or 

 three days. A height of 1000 feet would enable a bird to see a 

 ship 200 feet high more than fifty miles off"; and often, although 

 unable to see a ship itself, it would see another bird which had 

 evidently discovered one, and would follow it in the same way 

 that Vultures are known to follow one another. This opinion 

 is much strengthened by the fact that at sunrise very few birds 

 are round the ship, but soon afterwards they begin to arrive in 

 large numbers ; and I think I may safely say that this is always 



