138 Wild Life in a Southern County 



such slight openings existed. It was interesting to watch 

 their patient efforts as they clung to the perpendicular 

 wall like bats. Now, two or three flew off and described a 

 few circles in the air, as if to rest themselves, and then again 

 returned to work. At last, convinced of the impossibility 

 of penetrating the mortar, which was much harder beneath 

 the surface, they went away in a body with a general 

 twitter, leaving distinct marks of their shallow excava- 

 tions. The circumstance was the more interesting because 

 the road was much frequented (for a rural district), and 

 many people stopped to look at them ; but the birds did 

 not seem in the least alarmed, and evidently only left 

 because they found the wall impenetrable. Instinct, in- 

 fallible instinct, certainly would not direct these birds to 

 such an unsuitable spot. Neither was there any peculiar 

 advantage to attract them ; it was not quiet or retired, 

 but the reverse. The incident was clearly an experiment, 

 and when they found it unsuccessful they desisted. 



If we suppose this flight of martins to represent a 

 party emigrating from a sand quarry (there were three 

 such quarries within a mile radius), where the population 

 had overflowed, it seems possible to trace the motive which 

 animated them. I imagine that the old birds drive the 

 young ones away, when the young return to this country 

 with their parents after the annual migration. This is 

 particularly the case after a very favourable breeding 

 season, when more than the usual proportion of young 

 birds survive. After such a season, upon returning next 

 year to the sand quarry, the older birds drive off the 

 younger ; and if these are so numerous that they cannot 

 find room in another part of the quarry, they emigrate in 

 small parties. 



I think the same thing happens with rooks. The 



