WHY BIRDS FLOCK 221 



having nothing to fear from the eagle's attack because 

 of their combination ; and every one knows how a 



party of small birds will defy a hawk, or will 

 Why mob and rout a cuckoo or a day-flying owl. 

 Flock Possibly the reason for the great congregation 



of sparrows in one chosen tree in a London 

 square is mutual protection from cats. Food is a 

 most important factor in flocking ; the keeper knows 

 that the scarcer the food of partridges the greater is 

 their tendency to pack. Birds may pack at night for 

 mutual warmth as when titmice snuggle on branches, 

 and wrens, to the number of ten or twenty, crowd a hole 

 in the thatch. Partridges gain something in warmth in 

 snowy weather by their habit of jugging at night 

 a good covey on a yard of ground. But examination 

 of the spot where they have passed the night shows 

 that the main pack has been divided into compara- 

 tively small parties, in the same way as there were 

 small parties among the great herds of buffalo that 

 travelled as one column across the plains of America. 

 Sheltered hollows are naturally chosen for jugging, 

 where the keen edge of the wind passes over the 

 birds' heads. There is not always safety or benefit 

 in numbers ; a flock may attract foes where in- 

 dividuals would pass unnoticed, or may make short 

 work of food which would keep an individual for 

 many days. With insects, great congregations may 

 be harmful, if an advantage to their bird enemies. 

 Presumably, flocking is a matter of general con- 

 venience. 



