BEITISH WARBLERS 



only handle and examine these fragile organisms in order to 

 realize how prejudicial prolonged exposure must be to them. 

 So that even if we could not verify it by direct observation, 

 we should still have general reasons for believing that much 

 of the parents' time would be passed in brooding. Since 

 warmth and consequently freedom from exposure are of such 

 vital importance, does it seem unreasonable to suggest that 

 the covered nest would contribute towards that end, and by 

 freeing the parents of part of their task give rise to the habit 

 we observe in the case of some males ? We require evidence 

 from the lives of many species, whose young are nidicolous 

 and whose nests are protected, to show whether there is really 

 such a modification of behaviour as is here suggested. If a 

 covered nest does afford protection to the young and thus 

 allow greater freedom to the parents, it is clear that they will 

 have more time to seek the necessary food and will therefore 

 be in a position to rear a larger number of offspring ; I have 

 not, however, had sufficient time to investigate the matter 

 closely. Some facts relating to brooding will be found in the 

 lives of the Willow Warbler, Chiff-chaff, Whitethroat, Eeed 

 Warbler and Marsh Warbler. 



The methods adopted for feeding the young and for ensur- 

 ing the cleanliness of the nest involve a complicated series of 

 activities showing wonderful nicety of adaptation, and suggest 

 to my mind that the behaviour is purely instinctive. All the 

 species dealt with are very much alike in the treatment of 

 their offspring. I see no reason why a Garden Warbler should 

 not rear Whitethroats, or a Whitethroat Blackcaps, as success- 

 fully as their respective progeny. In fact, experiment proves 

 that such really is the case, for I have placed eggs of the 

 Whitethroat in a nest of the Garden Warbler and have 

 seen the young successfully reared. Some particular aspects 

 of the parental instinct are discussed in the histories of the 

 Whitethroat, Eeed Warbler and Marsh W^arbler. The normal 

 routine of tending the young is as follows : the parent arrives 

 at the nest with food and sometimes feeds one, more often two, 



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