BRITISH WARBLERS 



then there would be nothing to prevent any number of the 

 same species congregating within a very restricted area. 

 Consequently the food supply, which might have been ample 

 for the progeny of one pair of each of those species, would 

 become exhausted in the immediate vicinity of the nest. The 

 parent birds, therefore, instead of seeking and finding food 

 close at hand, would be compelled to travel further and further 

 afield, and thus the quick supply of food, so essential to the 

 welfare of the offspring, would not be forthcoming, and 

 correspondingly the interval for brooding, which is of such 

 importance during the early stages of growth, would be 

 diminished, with results that could only be detrimental, and 

 in cold wet seasons disastrous to the offspring. Apart 

 from these general considerations, my belief that the effect 

 of this law of territory has resulted in securing an efficient 

 food supply for the offspring in their early stages of growth is 

 based, in some measure, on the behaviour of certain birds, 

 both at the commencement of the period of sexual reproduc- 

 tion and after the young are able to take care of themselves. 

 If a pool, surrounded by agricultural land and occupied by a 

 number of Moorhens, is kept under observation early in the 

 season, it will be noticed that each morning at daybreak the 

 different individuals will wander over the land in search of 

 food. Now select some one particular pair, owning a territory, 

 and notice their behaviour. Any intrusion upon their domain 

 is resented; it is only necessary for an unpaired individual, 

 wandering amongst the rushes, to overstep the boundary, to call 

 forth a peculiar cry from the owner, followed by a determined 

 attack. Presently one or two individuals or pairs fly or run 

 out on to the fields to feed, causing a stir amongst the whole 

 community ; one bird follows another, the pair we are watching 

 swim towards the shore, join their neighbours, and in company 

 with them peaceably search for food. The fields are clearly 

 regarded as neutral ground, the territory itself being probably 

 not capable, so early in the season, of supplying the owners 

 with food. But when the young are hatched, the conditions 



