18 | R. COLLETT. [No. 3. É 
socks and the dense scrub, where, once in å way, å glimpse 
may be caught of an individual as it sneaks round å tuft or 
under a stone, or the sportsman's dog ferrets one out while rang- 
ing for willow grouse. | 
Traces of their proximity are, however, almost never want- 
ing. Here and there a heap of their easily recognized pel- 
lets of dung will be found outside the entrance to their bur- 
rows, as well as balls of hair on the tussocks; the latter are the 
castings of the meals of various rapacious birds, containing, 
generally, remnants of skulls or bones of the lemming. 
The nest is placed under a stone or beneath å tussock, in 
a copse of dwarf birches or juniper, and generally contains about 
5 young ones. Itis probable that, even in an ordinary year, at 
least two litters are produced during the summer, but definite 
observations in respect to this are still wanting. They feed ex- 
clusively on herbage, especially blades of grass and its roots, 
and also, during the winter, on the bark of mountain willows, 
(Salix lapponuum. S, glauca, S. phylteifolia, &c.). They are sought 
for by every kind of rapacious bird which inhabits the same 
heights, chiefly Archibuteo lagopus, as well as Falco tinnunculus, 
and, besides these, by Canis lagopus, and Mustela erminea. They 
form, too, the daily food of Nyctea scandiaca, and Asio brachyotus, 
notwithstanding that these, during ordinary years, appear, as å 
rule, more sporadically than the other above mentioned species. 
5. Prolific Years. 
Amongst numerous species of animals, a more or less in- 
creased productiveness occurs at irregular intervals, and species 
which, as å rule, appear in limited and inconspicuous numbers 
may, at such times, make their appearance in multitudes, or, at 
any rate, in greater numbers than usual. 
It is probably impossible to discover, in each instance, å 
satisfactory reason for this phenomenon. The rise may be due 


od 
on 
