150 LAND-BIRDS. 



considerably by the nature of the soil. Extremely interesting 

 details may be learned through the study of their excavations, 

 as these latter vary greatly in size, depth, and the angle at 

 which they run, in accordance with the variation of the soil. 

 The Bank Swallows invariably select a bank, the sand of which 

 will not " cave in," and then burrow to a stratum where the 

 pebbles, which might fall down upon their eggs or young, are 

 not found. Their colonies sometimes increase from year to 

 year with rapidity, and, if not disturbed, in the course of a 

 few seasons consist of a large number of excavations. 



How wonderful is that instinct which enables these Swallows 

 to find out the best places for their homes, and how wonderful 

 their skill in making these secure ! When a small party boldly 

 advance to a country hitherto unknown to them, who can de- 

 fine that sense which enables them to discover and select the 

 most fitting bank for their purposes, or even the best part of 

 it ? What, indeed, prompts them to part from their fellows 

 and to become pioneers in new settlements? Instinct can 

 never be fully understood by man, nor its workings. 



Wilson, speaking of the " Sand Martins," says : " We have 

 sometimes several days of cold rain and severe weather after 

 their arrival in spring, from which they take refuge in their 

 holes, clustering together for warmth, and have been fre- 

 quently found at such times in almost a lifeless state with the 

 cold, which circumstance has contributed to the belief that 

 they lie torpid all winter in these recesses." 



d. The Bank Swallows are usually more silent than the 

 other species, though one might not gather this impression 

 from a flock ; and their notes are less musical. 



V. PROGNE. 



A. SUBIS. Purple Martin. " Black Martin" Martin. 

 " Cape Cod Swallow.''' The Martins, though formerly abun- 

 dant, are now very generally rare in New England, being 

 confined to a few tracts of country and to localities.* 



* Although the Martin breeds extensive tracts of country which ap- 



throughout New England, as well as pear to he in every way suited to its 



still further to the northward, it is sin- habits, and returning to others, season 



gularly local in its distribution, avoiding after season, with unfailing regularity. 



