WILLOW WAEBLEB 



ferred, although level ground is occasionally Chosen, and in a 

 flat country must often be resorted to. As a rule one egg is 

 laid every twenty-four hours, but it sometimes happens that 

 a day is missed, in which case the loss of time is made up by 

 two being produced during the ensuing twenty-four hours. 

 Six or seven eggs represent the normal clutch, but if the first 

 nest is destroyed, the second clutch may consist of only three 

 or four eggs. Incubation lasts from twelve to thirteen days. 



It is possible to tell from the behaviour of the birds when 

 the young are hatched, since there is a marked increase in the 

 excitement they then show. This excitement may be said 

 to be almost equal to that shown during the period of sexual 

 activity. The period of incubation is a quiescent one ; the 

 male has nothing to do except to find food for himself, and 

 for the female it is a time for rest. The energy to some 

 extent exhausted during sexual activity is replenished, and 

 upon the appearance of the young finds an outlet. A com- 

 parison of the manner in which this energy asserts itself at 

 different periods forms one of the most interesting studies in 

 bird life, a study to which in the future considerable time and 

 attention must be devoted if we are to attain to a fuller know- 

 ledge of the meaning of the complex modes of behaviour, 

 which are comprised under the term " expression of the 

 emotions." I have just mentioned that, in the case of the 

 Willow Warbler, the excitement shown at the period of 

 parental care almost equals that at the period of sexual 

 activity, and I do not think this is an exaggeration, for it 

 would be a difficult task to draw a line between the two, or 

 even to point to a single action which could be regarded as 

 characteristic of only one period. It may be remembered 

 that during sexual activity both sexes flap their wings in a 

 peculiar manner. Upon the birth of the young I have seen 

 the parents behave similarly ; the female when near the male 

 flapped her wings in the manner indicative of a desire for 

 coition, and what is more curious still, coition appeared to be 

 the result. But it is perfectly clear that this could not have 



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