THE TUBE-NOSES 187 



shallow openings in the volcanic rock into which the sun may shine 

 upon the sitting birds. Soon after midday these great shearwaters 

 begin to assemble in vast numbers on the sea close to their island, 

 and long before sunset there is an exciting scene in the air as the 

 flocks begin to rise and come inland, circling overhead in thousands. 

 But where much persecuted by fishermen, as in the Berlengas Islands 

 off Portugal, and the Desertas off Madeira, this shearwater is 

 nocturnal. On Nightingale Island, Tristan da Cunha, Rowan (1952) 

 found the great shearwater {P. gravis) partly diurnal. 



With comparatively few other tubenoses is it possible to witness 

 this magnificent gathering of birds waiting to come to land. The 

 rafts of tens of thousands of Manx shearwaters off Skokholm and 

 Skomer in British waters are well known, but assemblies at sea of tube- 

 noses are more generally associated with a concentration of food, as 

 at whaling stations and trawling grounds. Many hundreds of fulmars 

 at one time may be seen on the water close to St. Kilda, and up to 

 5,000 may gather around one trawler at Rockall. J. T. Nichols (Bent, 

 1922) recorded over one thousand Wilson's petrels in sight at one time 

 from the coast of Long Island on 30 June 191 3. 



The courtship of the smaller petrels — ^Vilson's, Bulwer's, storm-. 

 Leach's, Madeiran and frigate-petrels, visiting their burrows at night — 

 has not been easy to study. Like the albatrosses of New Zealand, 

 storm-petrels at Skokholm (Lockley, 1932), Madeiran petrels on the 

 Desertas (Lockley, 1942) and Leach's petrels at North Rona (Ainslie 

 and Atkinson, 1937) have a circling flight over the nesting burrows 

 that appears to be partly a ceremonial dance, accompanied by excited 

 call-notes, very soft, of the storm- and Madeiran petrels, but by 

 a pleasant, almost musical, eight-syllabled cry of Leach's petrel. 

 Wilson's petrel has a similar night-flight, which Roberts considers is an 

 important part of their courtship, and utters a harsh call, generally as 

 the bird alights near its burrow when it chatters to its mate underground 

 and is answered. This night flying is characteristic of Bulwer's petrel, 

 but it is silent and not so prolonged, the incoming birds seeming to 

 circle for a short period as if orientating. As these circling flights 

 become localised the petrels drop down to their burrows and begin 

 the night's activities of burrowing, mating and incubating. Burrowing 

 by petrels and shearwaters is carried out by both sexes. The bill is 

 used as a pickaxe and the loose material thrown under the breast; 

 the webbed feet then drag and scatter it backwards down and out 

 of the burrow, as the bird lies now on one side and now on the other. 



