THE BANK-SWALLOW. 19 
pers to a point like a sailor’s marlinspike, or, rather, 
like the points of a pair of fine compasses when 
shut. If we compare this little sharp borer, as we 
may well call it, with the caliper-like mandibles of 
the sand-wasps (Sphecide, Leacu), and of the bur- 
rowing bees, which, like this swallow, excavate gal- 
leries proportionable to their size in hard sand,* we 
are compelled to confess that the bird is furnished 
with the more efficient instrument. Its operation 
also is very different. The insects alluded to gnaw 
into the sand, or, rather, bite off a portion of it, and 
carry it out of the hole in their mouths; but the 
bank-swallow, as we have had an opportunity of 
observing, works with its bill shut. This fact our 
readers may verify by observing their operations 
early in the morning, through an opera-glass, when 
they begin in the spring to form their excavations. 
In this way we have seen one of these swallows 
cling with its sharp claws to the face of a sandbank, 
and peg in its bill as a miner would do his pickaxe, 
till it had loosened a considerable portion of the hard, 
sand and tumbled it down among the rubbish below. 
In these preliminary operations it never makes use 
of its claws for digging; indeed, it is impossible it 
could, for they are indispensable in maintaining its 
position, at least when it is beginning its hole.t 
We have farther remarked that some of this swal- 
low’s holes are nearly as circular as if they had been 
planned out with a pair of compasses, while others 
are more irregular in form; but this seems to depend 
more on the sand crumbling away than upon any 
deficiency in the original workmanship. ‘The bird, 
in fact, always uses its own body to determine the 
proportions of the gallery, the part from the thigh 
to the head forming the radius of the circle. It | 
does not trace this out as we would do, by fixing a 
point for the centre around which to draw the cir- 
cumference. On the contrary, it perches on the 
* See Insect Architecture, chap. iii., &c. + J. Rennie. 
