ROOKS. 141 



At the lapse of a certain interval after sunset, they 

 are sure to be heard giving notice of their approach 

 by their united voices. The length or shortness of 

 this interval depends upon the time of the year and 

 the character of the weather. For the first fortnight 

 after midsummer, when the twilight is strong till 

 quite late in the evening, those that come home at 

 all do not return till near an hour after sunset. 

 The average time for their return during July I 

 find to be forty-five minutes after sunset, if the 

 weather be fine and clear ; but, if much overcast, 

 they generally shew themselves about ten minutes 

 earlier. 



In August as it gets more rapidly dusk, the inter- 

 val is reduced to about thirty or thirty-five minutes 

 after sunset; and in September it is still further 

 reduced, on an average to twenty-five minutes. 

 From all this it would seem that they are probably 

 guided by the light. Sometimes, when the weather 

 is damp and gloomy, but nevertheless mild, I observe 

 that they will return from feeding half an hour or an 

 hour earlier than usual, but do not retire actually to 

 the roost-trees till the accustomed time, employing 

 that interval in flying about in the neighbourhood, 

 or settling for a while on the trees that lie on the 

 outskirts of their immediate dormitory. When they 

 really betake themselves to rest, or for a few minutes 



mentioned above in respect of their returning at night to roost, is 

 certainly true in this neighbourhood, and the result of many suc- 

 cessive years' observations. The numbers so returning are some- 

 times very considerable, even as early as the first and second 

 weeks in July. 



