BIRDS IN AUTHORITY 49 



and authority over the females, compelling them 

 during the period of incubation to return to the nest 

 when they are inclined to stay out too long. Our 

 swift is a familiar example. But has anyone ever 

 observed an individual of any species, one of a colony, 

 presumably a male, exercising this kind of mastership 

 over a number of females in the absence of their 

 mates ? Yet this is exactly what I witnessed on 

 one occasion, and if I were to ask a dozen or fifty 

 naturalists to name the species they would all guess 

 wrong, for the bird in question was the small, deli- 

 cate, gentle, moth-like sand-martin — the "mountain 

 butterfly," as it is prettily named in Spain. 



Near Yeovil I found a breeding-place of these birds 

 in a vast old sand-pit. It was in May, and no doubt 

 they were incubating. There were about fifty holes 

 in the steepest side of the sand-bank, and when I 

 began watching them there were about fourteen or 

 fifteen birds flying round and round within the basin 

 of the pit, hawking after flies, and perhaps prolonging 

 their play-time after their morning feed. By-and-by 

 I noticed one bird acting in a singular manner; I 

 saw him come out of one hole and go quickly into 

 another, then another still, until he had visited several, 

 remaining about five or six seconds in each, or as long 

 as it would take him to run to the end of the burrow 

 and return. Finally, having finished inspecting the 

 holes, he began pursuing one of the birds flying 

 aimlessly about in the pit; the chase increased in 

 speed and violence until the hunted bird took refuge 

 in one of the burrows. He then started chasing 



