332 MB. B. COI/LETT ON MYOUES LEMMUS IN NORWAY. 



was no migration or hyper population of the Lemming, just aa 

 much as it did in those districts which were full of them. 



It will, I think, be rather difficult to state in what degree the 

 climate or the seasons have to do with fhis increase of animals in 

 certain years. Thus in 1862 the Blackcocks &c. (Tetraonidse) 

 in the southern parts of Norway were numerous to an extent 

 that probably has not been the case in any year since ; and a 

 great migration of the Lemming took place in the autumn in 

 the same localities : still it is a fact that the summer was propor- 

 tionally cold and rainy, and therefore, as may be suggested, not 

 particularly suitable to the bringing up of their young. The true 

 ground for the periodical increase in numbers is doubtless a phy- 

 siological necessity for the existence of the species, the reasons 

 for which at present it is beyond our power to explain. 



The wanderings take place in the direction of the valleys, and 

 therefore can branch out from the plateaux in any direction. 

 During migrations from the Dovre district the swarms wander 

 northwards through the valleys of Sondre Trondhjems Amt, as 

 much as southwards through Gudbrandsdalen and Osterdalen ; 

 from the district of Jotinsfjeldene and Langfjeldene the w^ander- 

 ings take the western direction to the innermost parts of Bergen 

 Stift, or an eastern course, and push their way down the valleys of 

 Valders, Hallingdal, and Nennedal. The most western valleys of 

 Norway, as in Bergen Stift, are proportionally less frequently visited 

 by them than the lowlands east of the high fells. From the High 

 fells towards the Swedish frontier, under 62° to 63° N. lat., the 

 wanderings branch out as much towards the districts bordering 

 the Trondhjems fjord as the Swedish provinces Jemteland and 

 Herjedalen, which in some years are covered with myriads of these 

 animals that all penetrate towards the Baltic. It is seldom that 

 the wandering flocks will cross a valley to reach a neighbouring 

 fell ; but sometimes they do : generally their course is somewhat 

 irregular, but, on the whole, in the direction of the valley itself. 

 They wander almost entirely in the night, and move quickly for- 

 wards. During the daytime they are, for the most part, resting 

 or hidden amongst stones or the tussocks, though considerable 

 numbers may be seen everywhere. Their temper and general 

 habits are so well known that I may here omit to mention them. 



During the seasons when they breed plentifully, the increase 

 takes place abundantly on the islands, which are sometimes very 

 small in extent ; as is the case with many of the mountainous 



