204 SEA-BIRDS 



impervious to water, roost or sleep at sea except in the breeding 

 season, but cormorants, shags and frigate-birds spend as much time 

 as possible on land or in the air, as already mentioned. Their loose 

 feathers are easily penetrated by water, and therefore they do not enter 

 it except when fishing; and after fishing they spend much time extend- 

 ing their wings^ and drying them in the wind and sunlight. They rest 

 and roost on sand, shingle, rocks, buoys and sea-marks, posts, trees, 

 even on electric power cables. Bartholomew (1943b) records 2,300 

 double-crested cormorants roosting at one time on a power line in 

 San Francisco Bay — a considerable strain on the cable. He found 

 that non-breeding cormorants contested for the best perching sites 

 on piles in California, but that the success of a fight depended not 

 on absolute "peck-right," as in the domestic fowl, but upon external 

 conditions such as the direction and speed of the wind, which governed 

 the approach of a bird wishing to land, and a bird might have to 

 crash its way through to a successful landing upon the overcrowded 

 perches. These contests were purely psychological and often ended in what 

 he terms "incomplete display," although the birds were non-breeders. 



The gannet and the pelican are extremely tenacious of their breed- 

 ing sites; many of the gannetries have been known to be occupied for 

 hundreds of years and doubtless some have been occupied for a thous- 

 and or more. The colony on Lundy was known to be occupied from 1 274 

 to 1909; that on the Bass Rock has been known since 1447, on Ailsa 

 Craig since 1526, on St. Kilda since 1696, on Sula Sgeir since 1549, 

 on the Westmann Islands since about 1687, on the Bird Rocks in the 

 Gulf of St. Lawrence since 1534. 



Where the colony is a large one, the gannet, like the guillemot, 

 returns correspondingly earlier in the spring. A few may settle on the 

 breeding cliff at the beginning of December, although it is usually 

 January before the best nesting sites (i.e., the oldest established ones) 

 are occupied: at least two months before the egg is laid. One of the 

 reasons for this early return has already been suggested: it is important 

 for successful breeding to claim desirable housing sites within the 

 densely packed colony. There is some evidence that the nest-sites on 

 the periphery, the region most exposed to outside influences such as 

 predatory animals and weather, are the last to be taken up — by the 

 younger inexperienced adult gannets, which are last to arrive, as in 

 the case of the tubenose and other sea-birds. 



All the pelicans breed in colonies, some less gregariously than 

 others, like shags which, though found in colonies, sometimes build in 



