20 THE ARCHITECTURE OF BIRDS. 



circumference with its claws, and works with its 

 bill from the centre outwards ; and hence it is that 

 in the numerous excavations recently commenced, 

 which we have examined, we have uniformly found 

 the termination funnel-shaped, the centre being al- 

 ways much more scooped out than the circumfer- 

 ence. The bird consequently assumes all positions 

 while at work in the interior, hanging from the roof 

 of the gallery with its back downward as often as 

 standing on the floor. We have more than once, 

 indeed, seen a bank-swallow wheeling slowly round 

 in this manner on the face of a sandbank when it 

 was just breaking ground to begin its gallery.* 



This manner of working, however, from the cir- 

 cumference to the centre, unavoidably leads to irreg- 

 ularities in the direction, which would not so read- 

 ily occur by reversing the procedure; for though 

 the radius formed by a part of the bird's body is 

 subject to little variation, yet the little that does oc- 

 cur from the extension or contraction of the neck, 

 must tend to throw it out of the right line. Accord- 

 ingly, all the galleries are found to be more or less 

 tortuous to their termination, which is at the depth 

 of from two to three feet, where a bed of loose hay 

 and a few of the smaller breast-feathers of geese, 

 ducks, or fowls are spread with little art for the re- 

 ception of the eggs.f 



It may not be unimportant to remark also, that it 

 always scrapes out with its feet the sand detached 

 by the bill ; but so carefully is this performed, that it 

 never scratches up the unmined sand or disturbs the 

 plane of the floor, which rather slopes upward, and, 

 of course, the lodgment of rain is thereby prevented. 

 The bank-swallow is eminently a social bird ; since 

 it not only always nestles in numerous colonies, but 

 also hunts for insects in troops of from three to fifty, 

 and, as Buffon correctly remarks, associates freely 

 with other swallows, 



* J. Rennie, t J. Rennie. 



