314 SWALLOWS AND MARTINS 



There can, however, be no doubt that both feed the young, and that, 

 like swallows and house-martins, they do so by regurgitating balls of 

 insects. Their mouths contain the same viscid saliva, and in the 

 mouth of one as many as nineteen insects have been found adhering 

 at the same time. 1 When the young are big enough they come to the 

 entrance of the nesting-hole, and, like young house-martins, keep 

 watch for the return of their parents, and call for them almost inces- 

 santly in harsh twittering notes. As far as my observation goes, only 

 one of the brood is fed at a time, the practice of sand-martins in this, 

 again, resembling that of house-martins. When fledged, the young 

 are fed in the air or on any convenient perch, and often, as before, 

 at the entrance of their holes. 



Those who have watched sand-martins, young or old, at their 

 breeding-place cannot fail to have noticed a curious habit they have of 

 clinging in a flock to the face of the cliff, not always motionless, but with 

 short hoverings and flutterings, as if trying to scramble higher up, 

 only suddenly, after a while, to fly off all together, and at the same time. 

 These movements are independent of the ordinary passing to and fro 

 to the nests of the birds engaged in feeding young. They are indulged 

 in by those that have, so to speak, time for relaxation. The sudden 

 flights off are, however, frequently joined by birds resting in or about 

 the entrance to their holes. On one occasion (July 21) when I 

 watched this play for such it appears to be I noted that a swallow, 

 a young one, took part in it, his presence being taken for granted. 

 There were no others of his species in view. 



Mr. E. Selous has noted a similar play on the part of sand- 

 martins when engaged in building their nests, and describes it as 

 follows : "We will suppose that the birds are now all working, either 

 inside their tunnels or clinging to the face of the cliff. All at once, 

 either at or about the same instant of time, they all fly off, darting 

 away, and disseminate themselves in the sky, not one being left in 

 or about the pit. In a few minutes they return, but . . . not in 



' Macgillivray, iii. 599, 604 ; and above, p. 289. 



