1895.] MYODES LEMMUS. 21 
color Will also have a prolific season in the lowlandsl, as well 
as (but more rarely) Arvicola glareolus. All these species might, 
naturally, have å multitudious increase at other times than dur- 
ing å prolific lemming year; but it is the rule, that all such 
cases occur simultaneously. 
In the northern tracts of the country it is chiefly A. rufo- 
camus?, and Å. ratticeps, which inhabit the regions of the Myodes, 
and both have often prolific years together with the latter. A 
similar multitudinous production has been observed in these 
parts at least on one occasion in Å. glareolus (Saltdalen near 
Bodö 1883). | 
To this may be added various other species of animais 
which are, as å rule, regarded as standing in åa certain depen- 
dent relationship to M. lemmus, as they, during the lemmings” 
migratory years, appear in far greater numbers than usual. This 
is the case with Mustela erminea, and, in part, with M. nivalis; 
furthermore, with Cams lagopus, Archibuteo lagopus, Falco aesalon 
and F. tinnunculus, as well as Nyctea scandiaca and Asio brachy- 
otus, besides many other birds of prey. 
It is presumed as å rule, that the frequent appearance of 
the mentioned species during such years is due to the super- 
abundant amount of food, as various consumers of the lemming 
are attracted from great distances around, to those places where 
the Myodes themselves are having å prolific or migratory year. 
This is hardly, however, the only reason for the inordinate 
number of these species during such years. They too are in- 
finenced by the fruitfulness of the year, and the birds of prey 
have therefore larger broods than is normally the case; Arcm- 
- butus lagopus has 5 og 6 young instead of 3 or 4, Nyctea scan- 
ME: report, stating that the M. schisticolor can have a prolific 
year simultaneously with M. lemmus, was made by Wegelin (Kgl. 
Vetensk. Akad. Förh. 1845, p. 188), who mentions that such occurred 
at Orsa in the province of Dalarne (Sweden) in 1848. (Up to that 
year the species had not even got its scientific description and name.) 
In Norway 4. rutilus has, hitherto, only been observed in the country 
about the Varanger Fjord. It is presumed that this species, too, has 
had prolific seasons at the same time as M. lemmus, but no fully reli- 
able observations have been published. 
] 
