GLACIAL EPOC LIS AND POLAR CLIMATES. 45 



by their strong addiction to nocturnal feeding now, 

 notwithstanding the fixct that their food (moUusks, 

 crustaceans, worms, and insects) may now as then be 

 obtained at all hours of the twenty-four. Of course 

 during spring and autumn they would be open 

 to the necessity or the inclination perhaps of feeding 

 by daylight as well as by night, whilst in summer 

 their nocturnal habits would be lost in eternal day. 

 Darkness would have little or no effect on seed- 

 eating birds, for their food supply would receive no 

 modification, and be as accessible in the dark as in 

 the light. Besides, these birds then as now did not 

 probably range into such high latitudes as to be 

 subject to the influence of Polar darkness ; they 

 doubtless dwelt in lower latitudes where the day 

 in winter w^ould be short, but sufficient for their 

 requirements ; and this fact is confirmed in what I 

 beheve to be a very startling way by the habit of 

 all seed-eating birds rising late and retiring early — 

 ivith the sun, in fact — even at the present day. A 

 tendency to nocturnal habits is the rule rather than 

 the exception among all northern and insectivorous 

 birds. The water birds are notoriously as much at 

 ease either by day or by night in their quest for 

 food. It is also a most remarkable fact that a very 

 high percentage of Arctic insectivorous Passerine 

 birds show a decided partiality for feeding at dusk. 

 Habits like these are neither acquired without cause 

 nor readily relinquished. The Redwing (Turdus 

 iliacus), the Fieldfare {Turdus pilaris), and the 

 Arctic Bluethroat [Erithacus s uecica} a,ve Sill birds 



