estris_ and _L. mutus_.
Mr. Ogilvie-Grant tells us of the former (p. 49), that it is merely a
more northern rufous form of _L. mutus_, and that it goes through
similar changes of plumage. In summer the males are readily
distinguishable, but in winter it is impossible to tell one from the
other. "_L. rupestris_ taken as a whole," says Mr. Ogilvie-Grant,
"appears to us barely specifically distinct from _L. mutus_." _L.
rupestris_ occurs not only in Northern Asia, but crosses the Behring
Straits to Arctic America, being still found on the Aleutian Islands,
which represent the last remains of the former land-bridge between Asia
and North America, then eastward to Greenland and Iceland. However,
while this form does not cross the confines of Asia in a westerly
direction, its near relative _L. mutus_--better known as the
Ptarmigan--does; and may perhaps have entered Europe as a Siberian and
also as an Arctic migrant. It is still found in the Ural Mountains, in
Finland, and the highlands of Scandinavia. It is gradually being driven
out of the Alpine lowlands, while it has long ago disappeared from
Germany, France, and Austria--in fact, from all the lowlands of Europe.
It has also been met with in the Pyrenees and in some of the Spanish
mountains. Similarly, the bird has become extinct in England and
Ireland, while it is becoming more and more scarce in Scotland. The
centre of distribution of the genus lies in Arctic America, and from
there the genus has spread to Europe and Asia. _L. albus_ and _L. mutus_
appear in our continent chiefly as Arctic migrants.

The Black Grouse (_Lyrurus tetrix_) belongs to a closely allied genus,
which has only two species. One of these is very local in distribution,
being confined to the Caucasus, but the smallness of range is to some
extent compensated for by the peculiarity of its name, which is _L.
mlokosiewiczi_. The Black Grouse, on the contrary, is widely
distributed. It inhabits Northern Asia from the Pacific to the Ural
Mountains, and extends as far south as Pekin and the Tian Shan range. In
Europe it is found from the extreme east to the Pyrenees, the Apennines
on the south, and to Great Britain and Scandinavia in the north. It is
important to note its absence from Spain, the Mediterranean islands, and
Ireland; and we have learned that it is one of those Siberian migrants
which have succeeded in establishing themselves in the Alps.

The Capercaillie (_Tetrao urogallus_)--another great