138 A HISTORY OF BIRDS 



demanded by these several species, for in those between which 

 these comparisons are made the food is practically the same. 

 Nor can it be attributed to relative differences in fertility, the 

 shy and retiring Rail, for example, having a far larger progeny 

 than the Plovers. It would seem then, that on the whole the 

 evidence favours the superiority of gregarious over solitary 

 habits. 



Among gregarious species some display a much more in- 

 timate association than others — -are more social in their relation- 

 ships. And this is shown very clearly in the devices which 

 some species have adopted for their mutual protection during 

 sleep. The Common Partridge, as is well known, lives in small 

 companies, or "coveys," which scatter only while feeding, 

 and then not far enough to be beyond call. Late in the day, 

 as soon " as the beetles begin to buzz," says Professor Newton, 

 the whole move away together to some spot where they jug, 

 as it is called — that is, squat and nestle close together for the 

 night ; and from the appearance of the mutings, or droppings, 

 which are generally deposited in a circle of only a few inches 

 in diameter, it would appear that the birds arrange themselves 

 also in a circle, of which their tails form the centre, all the heads 

 being outwards^a disposition which instinct has suggested as 

 the best for observing the approach of any of their numerous 

 enemies, whatever may be the direction, and thus increase their 

 security by enabling them to avoid a surprise. Ducks similarly 

 take special precautions to secure safety during sleep, when 

 this must be taken in exposed situations, as when, for example, 

 they desire to doze between the intervals of feeding during the 

 night, which they pass afloat. At such times they keep close 

 together, and to avoid drifting ashore keep one leg slowly 

 paddling and thus drive themselves round in circles. 



More remarkable still are those cases where a number of 

 birds crowd together in ball-like masses during sleep. Our British 

 Long-tailed Titmouse furnishes an example of this strange habit. 

 Similarly, the Crested Tree-swift of India roosts in this fashion, 

 forming feathery balls. The Wood-swallows {Artamida;) have 

 also adopted this practice. But the Australian species seem to 

 have carried it a stage further, inasmuch as instead of forming 

 a ball on the upper side of the bough, they are said to cling 

 together suspended from the under side. If this be so, one can 



