THE BIOGRAPHY OF A BIRD. 319 



they are indispensable in maintaining its position, at least when it is beginning 

 its hole. We have further remarked that some of these martins' 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 crum- 

 bling away than upon any deficiency in its 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 should do, by fixing a point for the centre around which to 

 draw the circumference : on the contrary, it perches on the circumference with 

 its claws, and works with its bill from the centre outward; . . . the bird con- 

 sequently assumes all positions wliile 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 martin wheeling slowly round in 

 this manner on the face of a sand-bank when it was just breaking ground to 

 begia its gallery. 



" This manner of working, however, from the circumference to the centre 

 unavoidably leads to irregularities in the direction. . . . Accordingly, 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, is spread with little art for the 

 reception of the four to six white eggs. 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 dis- 

 turbs the plane of the floor, which rather slopes upward, and of course the lodg- 

 ment of rain is thereby prevented." 



Sometimes the nest is carried to a far greater depth than two or 

 three feet, as in a case observed by Mr. Fowler, in Beverly, Massacliu- 

 setts, where, in order to get free of a stony soil where pebbles might be 

 dislodged and crush the eggs, the tunnel was carried in nine feet, while 

 neighboring birds in better soil only went a third as far. In one place 

 the burrows will be close to the top of tl)e bluff, in another near the 

 bottom, according as fancy dictates, or the birds have reason to fear 

 this or that enemy. English writers agree that occasionally their bank- 

 swallows do not dig holes, but lay in the crannies of old walls, and in 

 hollows of trees. This is never done, that I am aware of, in the United 

 States; but in California a closely allied species, the rough-winged 

 swallow, " sometimes resorts to natural clefts in the banks or adobe 

 buildings, and occasionally to knot-holes." On the great Plains, how- 

 ever, our Gotyle burrows in the slight embankments thrown up for 

 a railway-bed, in lieu of a better place, 



" How long does it take the bird to dig his cavei'n under ordinary 

 circumstances ? " is a question which it would seem hard to answer, con- 

 sidering the cryptic character of his work. Mr. W. H. Dall says four 

 days suffice to excavate the nest. Mr. Morris, a close observer of 

 British birds, says, per contra^ that a fortnight is required, and that 

 the bird removes twenty ounces of sand a day. Male and female 

 alternate in the labor of discojinff, and in the duties of incubation. 



When the female is sitting, you may thrust your arm in and grasp 



