330 ME. E. COLLETT ON MTODES LEMMITS IN NOEWAT. 



In the years of migration the families follow each other quickly, 

 and the set consists sometimes of nine, and not unusually of ten, 

 young. 



The greater number of those individuals that wander are young 

 and born in one of the last two years ; and I have observed that 

 they chiefly consist of males, the number of females being regu- 

 larly very small. 



The migration is brought to a close by the death of the swarms, 

 which is generally caused by an epizootic disease, the necessary 

 consequence of over-population. As this disease develops itself on 

 the high fells as well as on the lowlands, it cannot be caused by 

 the unusual mode of living of the wanderers ; for directly after 

 these migrations the high fells seem almost devoid of inhabitants. 

 The larger the masses, the higher is the mortality ; and this is in- 

 creased by the heat and want of drinking-water. During the 

 great migrations one can easily witness the sudden deaths amongst 

 the horde, many of their bodies appearing to be quite uninjured ; 

 though most of the specimens examined show the lower part of 

 the back almost denuded of hairs, and the skin covered with small 

 tubercles. These abrasions and pustules, in my opinion, are the 

 result of a disease of the skin, and not due to the habit of back- 

 ing up against a stone, or caused by their running into their 

 underground holes, as has been commonly affirmed. No individual 

 returns of its own will to the fells after it has once descended and 

 moved any distance from the plateaux. 



During the migrations they are devoured (besides by the mam- 

 mals and birds of prey of the above-mentioned species that fol- 

 low them down to the lowlands) chiefly by the Common Kestrel 

 {Faico tinnunculus), the Common Buzzard (Buteo vidgaris), all the 

 Owls (Striffidce), and the other birds of prey, the Weasel {Mustela 

 nivalis) and Fox (Vulpes vulgaris); further by Crows {Corvidce) 

 of different kinds, and in the northern parts of the country by 

 species of Gulls and Skuas (Larus and Lestris); and it must be 

 reckoned amongst the anomalies in the habits of the tame Eumi- 

 nants that they (chiefly the cattle and goats) sometimes betake 

 themselves to killing and eating the Lemmings. This is the case, 

 too, with the wild Eeindeer on the southern fells, and the same 

 in Finmarken. Numbers are killed by dogs and cats ; and men 

 everywhere try with all their power to diminish their numbers. 



The immediate reason for the large increase of Lemmings is 

 jrloubtless owing to exceptional circumstances repeated for some 



